Publications by authors named "Teresa Nicolson"

47 Publications

Putting the Pieces Together: the Hair Cell Transduction Complex.

J Assoc Res Otolaryngol 2021 12 6;22(6):601-608. Epub 2021 Oct 6.

Department of Otolaryngology-Head & Neck Surgery, Stanford University, Stanford, CA, USA.

Identification of the components of the mechanosensory transduction complex in hair cells has been a major research interest for many auditory and vestibular scientists and has attracted attention from outside the field. The past two decades have witnessed a number of significant advances with emergence of compelling evidence implicating at least a dozen distinct molecular components of the transduction machinery. Yet, how the pieces of this ensemble fit together and function in harmony to enable the senses of hearing and balance has not been clarified. The goal of this review is to summarize a 2021 symposium presented at the annual mid-winter meeting of the Association for Research in Otolaryngology. The symposium brought together the latest insights from within and beyond the field to examine individual components of the transduction complex and how these elements interact at molecular, structural, and biophysical levels to gate mechanosensitive channels and initiate sensory transduction in the inner ear. The review includes a brief historical background to set the stage for topics to follow that focus on structure, properties, and interactions of proteins such as CDH23, PCDH15, LHFPL5, TMIE, TMC1/2, and CIB2/3. We aim to present the diversity of ideas in this field and highlight emerging theories and concepts. This review will not only provide readers with a deeper appreciation of the components of the transduction apparatus and how they function together, but also bring to light areas of broad agreement, areas of scientific controversy, and opportunities for future scientific discovery.
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http://dx.doi.org/10.1007/s10162-021-00808-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8599550PMC
December 2021

Navigating Hereditary Hearing Loss: Pathology of the Inner Ear.

Authors:
Teresa Nicolson

Front Cell Neurosci 2021 20;15:660812. Epub 2021 May 20.

Department of Otolaryngology, Stanford University, Stanford, CA, United States.

Inherited forms of deafness account for a sizable portion of hearing loss among children and adult populations. Many patients with sensorineural deficits have pathological manifestations in the peripheral auditory system, the inner ear. Within the hearing organ, the cochlea, most of the genetic forms of hearing loss involve defects in sensory detection and to some extent, signaling to the brain the auditory cranial nerve. This review focuses on peripheral forms of hereditary hearing loss and how these impairments can be studied in diverse animal models or patient-derived cells with the ultimate goal of using the knowledge gained to understand the underlying biology and treat hearing loss.
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http://dx.doi.org/10.3389/fncel.2021.660812DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8172992PMC
May 2021

Temporal Vestibular Deficits in () Mutants.

Front Mol Neurosci 2020 18;13:604189. Epub 2021 Jan 18.

Department of Otolaryngology, Stanford University, Stanford, CA, United States.

The lipid phosphatase is required for the disassembly of clathrin coats on endocytic compartments. In neurons such activity is necessary for the recycling of endocytosed membrane into synaptic vesicles. Mutations in zebrafish have been shown to disrupt the activity of ribbon synapses in sensory hair cells. After prolonged mechanical stimulation of hair cells, both phase locking of afferent nerve activity and the recovery of spontaneous release of synaptic vesicles are diminished in mutants. Presumably as a behavioral consequence of these synaptic deficits, mutants are unable to maintain an upright posture. To probe vestibular function with respect to postural control in mutants, we developed a method for assessing the vestibulospinal reflex (VSR) in larvae. We elicited the VSR by rotating the head and recorded tail movements. As expected, the VSR is completely absent in and mutants that lack inner ear function. Conversely, mutants, which have a selective loss of function of the lateral line organ, have normal VSRs, suggesting that the hair cells of this organ do not contribute to this reflex. In contrast to mechanotransduction mutants, the mutant produces normal tail movements during the initial cycles of rotation of the head. Both the amplitude and temporal aspects of the response are unchanged. However, after several rotations, the VSR in mutants was strongly diminished or absent. Mutant larvae are able to recover, but the time required for the reappearance of the VSR after prolonged stimulation is dramatically increased in mutants. Collectively, the data demonstrate a behavioral correlate of the synaptic defects caused by the loss of function. Our results suggest that defects in synaptic vesicle recycling give rise to fatigue of ribbons synapses and possibly other synapses of the VS circuit, leading to the loss of postural control.
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http://dx.doi.org/10.3389/fnmol.2020.604189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7874208PMC
January 2021

Disruption of Genes in Zebrafish Reveals Subunit Requirements in Subtypes of Inner Ear Hair Cells.

J Neurosci 2020 06 5;40(23):4457-4468. Epub 2020 May 5.

Department of Otolaryngology Head and Neck Surgery, Stanford School of Medicine, Stanford University, Stanford, California 94305

Detection of sound and head movement requires mechanoelectrical transduction (MET) channels at tips of hair-cell stereocilia. In vertebrates, the transmembrane channel-like (TMC) proteins TMC1 and TMC2 fulfill critical roles in MET, and substantial evidence implicates these TMCs as subunits of the MET channel. To identify developmental and functional roles of this Tmc subfamily in the zebrafish inner ear, we tested the effects of truncating mutations in , , and on mechanosensation at the onset of hearing and balance, before gender differentiation. We find that triple-mutant larvae cannot detect sound or orient with respect to gravity. They lack acoustic-evoked behavioral responses, vestibular-induced eye movements, and hair-cell activity as assessed with FM dye labeling and microphonic potentials. Despite complete loss of hair-cell function, triple-mutant larvae retain normal gross morphology of hair bundles and proper trafficking of known MET components Protocadherin 15a (Pcdh15a), Lipoma HMGIC fusion partner-like 5 (Lhfpl5), and Transmembrane inner ear protein (Tmie). Transgenic, hair cell-specific expression of Tmc2b-mEGFP rescues the behavioral and physiological deficits in triple mutants. Results from single and double mutants evince a principle role for Tmc2a and Tmc2b in hearing and balance, respectively, whereas Tmc1 has lower overall impact. Our experiments reveal that, in developing cristae, hair cells stratify into an upper, Tmc2a-dependent layer of teardrop-shaped cells and a lower, Tmc1/2b-dependent tier of gourd-shaped cells. Collectively, our genetic evidence indicates that auditory/vestibular end organs and subsets of hair cells therein rely on distinct combinations of Tmc1/2a/2b. We assessed the effects of truncation mutations on mechanoelectrical transduction (MET) in the inner-ear hair cells of larval zebrafish. triple mutants lacked behavioral responses to sound and head movements, while further assays demonstrated no observable mechanosensitivity in the triple mutant inner ear. Examination of double mutants revealed major contributions from Tmc2a and Tmc2b to macular function; however, Tmc1 had less overall impact. FM labeling of lateral cristae in double mutants revealed the presence of two distinct cell types, an upper layer of teardrop-shaped cells that rely on Tmc2a, and a lower layer of gourd-shaped cells that rely on Tmc1/2b.
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http://dx.doi.org/10.1523/JNEUROSCI.0163-20.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7275854PMC
June 2020

The Ohnologs and 5b Are Required for Mechanotransduction in Distinct Populations of Sensory Hair Cells in Zebrafish.

Front Mol Neurosci 2019 15;12:320. Epub 2020 Jan 15.

Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR, United States.

Hair cells sense and transmit auditory, vestibular, and hydrodynamic information by converting mechanical stimuli into electrical signals. This process of mechano-electrical transduction (MET) requires a mechanically gated channel localized in the apical stereocilia of hair cells. In mice, lipoma HMGIC fusion partner-like 5 (LHFPL5) acts as an auxiliary subunit of the MET channel whose primary role is to correctly localize PCDH15 and TMC1 to the mechanotransduction complex. Zebrafish have two genes ( and ), but their individual contributions to MET channel assembly and function have not been analyzed. Here we show that the zebrafish genes are expressed in discrete populations of hair cells: expression is restricted to auditory and vestibular hair cells in the inner ear, while expression is specific to hair cells of the lateral line organ. Consequently, mutants exhibit defects in auditory and vestibular function, while disruption of affects hair cells only in the lateral line neuromasts. In contrast to previous reports in mice, localization of Tmc1 does not depend upon Lhfpl5 function in either the inner ear or lateral line organ. In both and mutants, GFP-tagged Tmc1 and Tmc2b proteins still localize to the stereocilia of hair cells. Using a stably integrated GFP-Lhfpl5a transgene, we show that the tip link cadherins Pcdh15a and Cdh23, along with the Myo7aa motor protein, are required for correct Lhfpl5a localization at the tips of stereocilia. Our work corroborates the evolutionarily conserved co-dependence between Lhfpl5 and Pcdh15, but also reveals novel requirements for Cdh23 and Myo7aa to correctly localize Lhfpl5a. In addition, our data suggest that targeting of Tmc1 and Tmc2b proteins to stereocilia in zebrafish hair cells occurs independently of Lhfpl5 proteins.
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http://dx.doi.org/10.3389/fnmol.2019.00320DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6974483PMC
January 2020

Subunits of the mechano-electrical transduction channel, Tmc1/2b, require Tmie to localize in zebrafish sensory hair cells.

PLoS Genet 2019 02 6;15(2):e1007635. Epub 2019 Feb 6.

Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, Portland, Oregon, United States of America.

Mutations in transmembrane inner ear (TMIE) cause deafness in humans; previous studies suggest involvement in the mechano-electrical transduction (MET) complex in sensory hair cells, but TMIE's precise role is unclear. In tmie zebrafish mutants, we observed that GFP-tagged Tmc1 and Tmc2b, which are subunits of the MET channel, fail to target to the hair bundle. In contrast, overexpression of Tmie strongly enhances the targeting of Tmc1-GFP and Tmc2b-GFP to stereocilia. To identify the motifs of Tmie underlying the regulation of the Tmcs, we systematically deleted or replaced peptide segments. We then assessed localization and functional rescue of each mutated/chimeric form of Tmie in tmie mutants. We determined that the first putative helix was dispensable and identified a novel critical region of Tmie, the extracellular region and transmembrane domain, which is required for both mechanosensitivity and Tmc2b-GFP expression in bundles. Collectively, our results suggest that Tmie's role in sensory hair cells is to target and stabilize Tmc channel subunits to the site of MET.
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http://dx.doi.org/10.1371/journal.pgen.1007635DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6380590PMC
February 2019

Zebrafish: from genes and neurons to circuits, behavior and disease.

J Neurogenet 2017 09;31(3):59-60

e Department of Biology , University of Iowa , Iowa City , IA , USA.

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http://dx.doi.org/10.1080/01677063.2017.1359589DOI Listing
September 2017

The genetics of hair-cell function in zebrafish.

Authors:
Teresa Nicolson

J Neurogenet 2017 09 13;31(3):102-112. Epub 2017 Jul 13.

a Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University , Portland , OR , USA.

Our ears are remarkable sensory organs, providing the important senses of balance and hearing. The complex structure of the inner ear, or 'labyrinth', along with the assorted neuroepithelia, have evolved to detect head movements and sounds with impressive sensitivity. The rub is that the inner ear is highly vulnerable to genetic lesions and environmental insults. According to National Institute of Health estimates, hearing loss is one of the most commonly inherited or acquired sensorineural diseases. To understand the causes of deafness and balance disorders, it is imperative to understand the underlying biology of the inner ear, especially the inner workings of the sensory receptors. These receptors, which are termed hair cells, are particularly susceptible to genetic mutations - more than two dozen genes are associated with defects in this cell type in humans. Over the past decade, a substantial amount of progress has been made in working out the molecular basis of hair-cell function using vertebrate animal models. Given the transparency of the inner ear and the genetic tools that are available, zebrafish have become an increasingly popular animal model for the study of deafness and vestibular dysfunction. Mutagenesis screens for larval defects in hearing and balance have been fruitful in finding key components, many of which have been implicated in human deafness. This review will focus on the genes that are required for hair-cell function in zebrafish, with a particular emphasis on mechanotransduction. In addition, the generation of new tools available for the characterization of zebrafish hair-cell mutants will be discussed.
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http://dx.doi.org/10.1080/01677063.2017.1342246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6080859PMC
September 2017

Enlargement of Ribbons in Zebrafish Hair Cells Increases Calcium Currents But Disrupts Afferent Spontaneous Activity and Timing of Stimulus Onset.

J Neurosci 2017 06 25;37(26):6299-6313. Epub 2017 May 25.

Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders/National Institutes of Health, Bethesda, Maryland 20892,

In sensory hair cells of auditory and vestibular organs, the ribbon synapse is required for the precise encoding of a wide range of complex stimuli. Hair cells have a unique presynaptic structure, the synaptic ribbon, which organizes both synaptic vesicles and calcium channels at the active zone. Previous work has shown that hair-cell ribbon size is correlated with differences in postsynaptic activity. However, additional variability in postsynapse size presents a challenge to determining the specific role of ribbon size in sensory encoding. To selectively assess the impact of ribbon size on synapse function, we examined hair cells in transgenic zebrafish that have enlarged ribbons, without postsynaptic alterations. Morphologically, we found that enlarged ribbons had more associated vesicles and reduced presynaptic calcium-channel clustering. Functionally, hair cells with enlarged ribbons had larger global and ribbon-localized calcium currents. Afferent neuron recordings revealed that hair cells with enlarged ribbons resulted in reduced spontaneous spike rates. Additionally, despite larger presynaptic calcium signals, we observed fewer evoked spikes with longer latencies from stimulus onset. Together, our work indicates that hair-cell ribbon size influences the spontaneous spiking and the precise encoding of stimulus onset in afferent neurons. Numerous studies support that hair-cell ribbon size corresponds with functional sensitivity differences in afferent neurons and, in the case of inner hair cells of the cochlea, vulnerability to damage from noise trauma. Yet it is unclear whether ribbon size directly influences sensory encoding. Our study reveals that ribbon enlargement results in increased ribbon-localized calcium signals, yet reduces afferent spontaneous activity and disrupts the timing of stimulus onset, a distinct aspect of auditory and vestibular encoding. These observations suggest that varying ribbon size alone can influence sensory encoding, and give further insight into how hair cells transduce signals that cover a wide dynamic range of stimuli.
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http://dx.doi.org/10.1523/JNEUROSCI.2878-16.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5490065PMC
June 2017

Integration of Tmc1/2 into the mechanotransduction complex in zebrafish hair cells is regulated by Transmembrane O-methyltransferase (Tomt).

Elife 2017 05 23;6. Epub 2017 May 23.

Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States.

Transmembrane O-methyltransferase (/) is responsible for non-syndromic deafness DFNB63. However, the specific defects that lead to hearing loss have not been described. Using a zebrafish model of DFNB63, we show that the auditory and vestibular phenotypes are due to a lack of mechanotransduction (MET) in Tomt-deficient hair cells. GFP-tagged Tomt is enriched in the Golgi of hair cells, suggesting that Tomt might regulate the trafficking of other MET components to the hair bundle. We found that Tmc1/2 proteins are specifically excluded from the hair bundle in mutants, whereas other MET complex proteins can still localize to the bundle. Furthermore, mouse TOMT and TMC1 can directly interact in HEK 293 cells, and this interaction is modulated by His183 in TOMT. Thus, we propose a model of MET complex assembly where Tomt and the Tmcs interact within the secretory pathway to traffic Tmc proteins to the hair bundle.
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http://dx.doi.org/10.7554/eLife.28474DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5462536PMC
May 2017

Functional Analysis of the Transmembrane and Cytoplasmic Domains of Pcdh15a in Zebrafish Hair Cells.

J Neurosci 2017 03 20;37(12):3231-3245. Epub 2017 Feb 20.

Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239

Protocadherin 15 (PCDH15) is required for mechanotransduction in sensory hair cells as a component of the tip link. Isoforms of PCDH15 differ in their cytoplasmic domains (CD1, CD2, and CD3), but share the extracellular and transmembrane (TMD) domains, as well as an intracellular domain known as the common region (CR). In heterologous expression systems, both the TMD and CR of PCDH15 have been shown to interact with members of the mechanotransduction complex. The significance of these protein-protein interaction domains of PCDH15 in hair cells has not been determined. Here, we examined the localization and function of the two isoforms of zebrafish Pcdh15a (CD1 and CD3) in -null mutants by assessing Pcdh15a transgene-mediated rescue of auditory/vestibular behavior and hair cell morphology and activity. We found that either isoform alone was able to rescue the Pcdh15a-null phenotype and that the CD1- or CD3-specific regions were dispensable for hair bundle integrity and labeling of hair cells with FM4-64, which was used as a proxy for mechanotransduction. When either the CR or TMD domain was deleted, the mutated proteins localized to the stereocilial tips, but were unable to rescue FM4-64 labeling. Disrupting both domains led to a complete failure of Pcdh15a to localize to the hair bundle. Our findings demonstrate that the TMD and cytoplasmic CR domains are required for the function of Pcdh15a in zebrafish hair cells. Tip links transmit force to mechanotransduction channels at the tip of hair bundles in sensory hair cells. One component of tip links is Protocadherin 15 (PCDH15). Here, we demonstrate that, when transgenically expressed, either zebrafish Pcdh15a-cytodomain 1 (CD1) or Pcdh15a-CD3 can rescue the phenotype of a -null mutant. Even when lacking the specific regions for CD1 or CD3, truncated Pcdh15a that contains the so-called common region (CR) at the cytoplasmic/membrane interface still has the ability to rescue similar to full-length Pcdh15a. In contrast, Pcdh15a lacking the entire cytoplasmic domain is not functional. These results demonstrate that the CR plays a key role in the mechanotransduction complex in hair cells.
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http://dx.doi.org/10.1523/JNEUROSCI.2216-16.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5373116PMC
March 2017

Dopamine Modulates the Activity of Sensory Hair Cells.

J Neurosci 2015 Dec;35(50):16494-503

Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239

Unlabelled: The senses of hearing and balance are subject to modulation by efferent signaling, including the release of dopamine (DA). How DA influences the activity of the auditory and vestibular systems and its site of action are not well understood. Here we show that dopaminergic efferent fibers innervate the acousticolateralis epithelium of the zebrafish during development but do not directly form synapses with hair cells. However, a member of the D1-like receptor family, D1b, tightly localizes to ribbon synapses in inner ear and lateral-line hair cells. To assess modulation of hair-cell activity, we reversibly activated or inhibited D1-like receptors (D1Rs) in lateral-line hair cells. In extracellular recordings from hair cells, we observed that D1R agonist SKF-38393 increased microphonic potentials, whereas D1R antagonist SCH-23390 decreased microphonic potentials. Using ratiometric calcium imaging, we found that increased D1R activity resulted in larger calcium transients in hair cells. The increase of intracellular calcium requires Cav1.3a channels, as a Cav1 calcium channel antagonist, isradipine, blocked the increase in calcium transients elicited by the agonist SKF-38393. Collectively, our results suggest that DA is released in a paracrine fashion and acts at ribbon synapses, likely enhancing the activity of presynaptic Cav1.3a channels and thereby increasing neurotransmission.

Significance Statement: The neurotransmitter dopamine acts in a paracrine fashion (diffusion over a short distance) in several tissues and bodily organs, influencing and regulating their activity. The cellular target and mechanism of the action of dopamine in mechanosensory organs, such as the inner ear and lateral-line organ, is not clearly understood. Here we demonstrate that dopamine receptors are present in sensory hair cells at synaptic sites that are required for signaling to the brain. When nearby neurons release dopamine, activation of the dopamine receptors increases the activity of these mechanosensitive cells. The mechanism of dopamine activation requires voltage-gated calcium channels that are also present at hair-cell synapses.
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http://dx.doi.org/10.1523/JNEUROSCI.1691-15.2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4679827PMC
December 2015

Identification of sensory hair-cell transcripts by thiouracil-tagging in zebrafish.

BMC Genomics 2015 Oct 23;16:842. Epub 2015 Oct 23.

Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR, 97239, USA.

Background: Sensory hair cells are exquisitely sensitive to mechanical stimuli and as such, are prone to damage and apoptosis during dissections or in vitro manipulations. Thiouracil (TU)-tagging is a noninvasive method to label cell type-specific transcripts in an intact organism, thereby meeting the challenge of how to analyze gene expression in hair cells without the need to sort cells. We adapted TU-tagging to zebrafish to identify novel transcripts expressed in the sensory hair cells of the developing acoustico-lateralis organs.

Methods: We created a transgenic line of zebrafish expressing the T.gondii uracil phospho-ribosyltransferase (UPRT) enzyme specifically in the hair cells of the inner ear and lateral line organ. RNA was labeled by exposing 3 days post-fertilization (dpf) UPRT transgenic larvae to 2.5 mM 4-thiouracil (4TU) for 15 hours. Following total RNA isolation, poly(A) mRNA enrichment, and purification of TU-tagged RNA, deep sequencing was performed on the input and TU-tagged RNA samples.

Results: Analysis of the RNA sequencing data revealed the expression of 28 transcripts that were significantly enriched (adjusted p-value < 0.05) in the UPRT TU-tagged RNA relative to the input sample. Of the 25 TU-tagged transcripts with mammalian homologs, the expression of 18 had not been previously demonstrated in zebrafish hair cells. The hair cell-restricted expression for 17 of these transcripts was confirmed by whole mount mRNA in situ hybridization in 3 dpf larvae.

Conclusions: The hair cell-restricted pattern of expression of these genes offers insight into the biology of this receptor cell type and may serve as useful markers to study the development and function of sensory hair cells. In addition, our study demonstrates the utility of TU-tagging to study nascent transcripts in specific cell types that are relatively rare in the context of the whole zebrafish larvae.
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http://dx.doi.org/10.1186/s12864-015-2072-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4619078PMC
October 2015

It takes two.

Authors:
Teresa Nicolson

Elife 2015 Oct 6;4. Epub 2015 Oct 6.

Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States.

Two forms of an unconventional myosin motor protein have separate functions in the growth and maintenance of hair bundles in auditory hair cells.
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http://dx.doi.org/10.7554/eLife.11399DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592937PMC
October 2015

Characterization of Ribeye subunits in zebrafish hair cells reveals that exogenous Ribeye B-domain and CtBP1 localize to the basal ends of synaptic ribbons.

PLoS One 2014 10;9(9):e107256. Epub 2014 Sep 10.

Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, Portland, Oregon, United States of America.

Synaptic ribbons are presynaptic structures formed by the self-association of RIBEYE-the main structural component of ribbon synapses. RIBEYE consists of two domains: a unique N-terminal A-domain and a C-terminal B-domain that is identical to the transcription co-repressor C-terminal binding protein 2 (CtBP2). Previous studies in cell lines have shown that RIBEYE A-domain alone is sufficient to form ribbon-like aggregates and that both A- and B- domains form homo-and heterotypic interactions. As these interactions are likely the basis for synaptic-ribbon assembly and structural plasticity, we wanted to examine how zebrafish Ribeye A- and B- domains interact with synaptic ribbons in vivo. To that end, we characterized the localization of exogenously expressed Ribeye A- and B- domains and the closely related protein, CtBP1, in the hair cells of transgenic zebrafish larvae. Unexpectedly, exogenously expressed Ribeye A-domain showed variable patterns of localization in hair cells; one zebrafish paralog of A-domain failed to self-associate or localize to synaptic ribbons, while the other self-assembled but sometimes failed to localize to synaptic ribbons. By contrast, Ribeye B-domain/CtBP2 was robustly localized to synaptic ribbons. Moreover, both exogenously expressed B-domain/CtBP2 and CtBP1 were preferentially localized to the basal end of ribbons adjacent to the postsynaptic density. Overexpression of B-domain/CtBP2 also appeared to affect synaptic-ribbon composition; endogenous levels of ribbon-localized Ribeye were significantly reduced as hair cells matured in B-domain/CtBP2 transgenic larvae compared to wild-type. These results reveal how exogenously expressed Ribeye domains interact with synaptic ribbons, and suggest a potential organization of elements within the ribbon body.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0107256PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4160224PMC
March 2016

Tip-link protein protocadherin 15 interacts with transmembrane channel-like proteins TMC1 and TMC2.

Proc Natl Acad Sci U S A 2014 Sep 11;111(35):12907-12. Epub 2014 Aug 11.

Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR 97239

The tip link protein protocadherin 15 (PCDH15) is a central component of the mechanotransduction complex in auditory and vestibular hair cells. PCDH15 is hypothesized to relay external forces to the mechanically gated channel located near its cytoplasmic C terminus. How PCDH15 is coupled to the transduction machinery is not clear. Using a membrane-based two-hybrid screen to identify proteins that bind to PCDH15, we detected an interaction between zebrafish Pcdh15a and an N-terminal fragment of transmembrane channel-like 2a (Tmc2a). Tmc2a is an ortholog of mammalian TMC2, which along with TMC1 has been implicated in mechanotransduction in mammalian hair cells. Using the above-mentioned two-hybrid assay, we found that zebrafish Tmc1 and Tmc2a can interact with the CD1 or CD3 cytoplasmic domain isoforms of Pcdh15a, and this interaction depends on the common region shared between the two Pcdh15 isoforms. Moreover, an interaction between mouse PCDH15-CD3 and TMC1 or TMC2 was observed in both yeast two-hybrid assays and coimmunoprecipitation experiments. To determine whether the Pcdh15-Tmc interaction is relevant to mechanotransduction in vivo, we overexpressed N-terminal fragments of Tmc2a in zebrafish hair cells. Overexpression of the Tmc2a N terminus results in mislocalization of Pcdh15a within hair bundles, together with a significant decrease in mechanosensitive responses, suggesting that a Pcdh15a-Tmc complex is critical for mechanotransduction. Together, these results identify an evolutionarily conserved association between the fish and mouse orthologs of PCDH15 and TMC1 and TMC2, supporting the notion that TMCs are key components of the transduction complex in hair cells.
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http://dx.doi.org/10.1073/pnas.1402152111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4156717PMC
September 2014

Who needs tip links? Backwards transduction by hair cells.

J Gen Physiol 2013 Nov 14;142(5):481-6. Epub 2013 Oct 14.

Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, Portland, OR 97239.

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http://dx.doi.org/10.1085/jgp.201311111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3813381PMC
November 2013

Mutations in ap1b1 cause mistargeting of the Na(+)/K(+)-ATPase pump in sensory hair cells.

PLoS One 2013 12;8(4):e60866. Epub 2013 Apr 12.

Oregon Hearing Research Center and Vollum Institute, Howard Hughes Medical Institute, Oregon Health and Science University, Portland, Oregon, USA.

The hair cells of the inner ear are polarized epithelial cells with a specialized structure at the apical surface, the mechanosensitive hair bundle. Mechanotransduction occurs within the hair bundle, whereas synaptic transmission takes place at the basolateral membrane. The molecular basis of the development and maintenance of the apical and basal compartments in sensory hair cells is poorly understood. Here we describe auditory/vestibular mutants isolated from forward genetic screens in zebrafish with lesions in the adaptor protein 1 beta subunit 1 (ap1b1) gene. Ap1b1 is a subunit of the adaptor complex AP-1, which has been implicated in the targeting of basolateral membrane proteins. In ap1b1 mutants we observed that although the overall development of the inner ear and lateral-line organ appeared normal, the sensory epithelium showed progressive signs of degeneration. Mechanically-evoked calcium transients were reduced in mutant hair cells, indicating that mechanotransduction was also compromised. To gain insight into the cellular and molecular defects in ap1b1 mutants, we examined the localization of basolateral membrane proteins in hair cells. We observed that the Na(+)/K(+)-ATPase pump (NKA) was less abundant in the basolateral membrane and was mislocalized to apical bundles in ap1b1 mutant hair cells. Accordingly, intracellular Na(+) levels were increased in ap1b1 mutant hair cells. Our results suggest that Ap1b1 is essential for maintaining integrity and ion homeostasis in hair cells.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0060866PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625210PMC
October 2013

Towards a comprehensive catalog of zebrafish behavior 1.0 and beyond.

Zebrafish 2013 Mar;10(1):70-86

Department of Pharmacology and Neuroscience Program, Tulane University Medical School, 1430 Tulane Avenue, New Orleans, LA 70112, USA.

Zebrafish (Danio rerio) are rapidly gaining popularity in translational neuroscience and behavioral research. Physiological similarity to mammals, ease of genetic manipulations, sensitivity to pharmacological and genetic factors, robust behavior, low cost, and potential for high-throughput screening contribute to the growing utility of zebrafish models in this field. Understanding zebrafish behavioral phenotypes provides important insights into neural pathways, physiological biomarkers, and genetic underpinnings of normal and pathological brain function. Novel zebrafish paradigms continue to appear with an encouraging pace, thus necessitating a consistent terminology and improved understanding of the behavioral repertoire. What can zebrafish 'do', and how does their altered brain function translate into behavioral actions? To help address these questions, we have developed a detailed catalog of zebrafish behaviors (Zebrafish Behavior Catalog, ZBC) that covers both larval and adult models. Representing a beginning of creating a more comprehensive ethogram of zebrafish behavior, this effort will improve interpretation of published findings, foster cross-species behavioral modeling, and encourage new groups to apply zebrafish neurobehavioral paradigms in their research. In addition, this glossary creates a framework for developing a zebrafish neurobehavioral ontology, ultimately to become part of a unified animal neurobehavioral ontology, which collectively will contribute to better integration of biological data within and across species.
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http://dx.doi.org/10.1089/zeb.2012.0861DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3629777PMC
March 2013

Presynaptic CaV1.3 channels regulate synaptic ribbon size and are required for synaptic maintenance in sensory hair cells.

J Neurosci 2012 Nov;32(48):17273-86

Howard Hughes Medical Institute, Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239, USA.

L-type calcium channels (Ca(V)1) are involved in diverse processes, such as neurotransmission, hormone secretion, muscle contraction, and gene expression. In this study, we uncover a role for Ca(V)1.3a in regulating the architecture of a cellular structure, the ribbon synapse, in developing zebrafish sensory hair cells. By combining in vivo calcium imaging with confocal and super-resolution structured illumination microscopy, we found that genetic disruption or acute block of Ca(V)1.3a channels led to enlargement of synaptic ribbons in hair cells. Conversely, activating channels reduced both synaptic-ribbon size and the number of intact synapses. Along with enlarged presynaptic ribbons in ca(V)1.3a mutants, we observed a profound loss of juxtaposition between presynaptic and postsynaptic components. These synaptic defects are not attributable to loss of neurotransmission, because vglut3 mutants lacking neurotransmitter release develop relatively normal hair-cell synapses. Moreover, regulation of synaptic-ribbon size by Ca(2+) influx may be used by other cell types, because we observed similar pharmacological effects on pinealocyte synaptic ribbons. Our results indicate that Ca(2+) influx through Ca(V)1.3 fine tunes synaptic ribbon size during hair-cell maturation and that Ca(V)1.3 is required for synaptic maintenance.
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http://dx.doi.org/10.1523/JNEUROSCI.3005-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3718275PMC
November 2012

Rapid positional cloning of zebrafish mutations by linkage and homozygosity mapping using whole-genome sequencing.

Development 2012 Nov 10;139(22):4280-90. Epub 2012 Oct 10.

Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.

Forward genetic screens in zebrafish have identified >9000 mutants, many of which are potential disease models. Most mutants remain molecularly uncharacterized because of the high cost, time and labor investment required for positional cloning. These costs limit the benefit of previous genetic screens and discourage future screens. Drastic improvements in DNA sequencing technology could dramatically improve the efficiency of positional cloning in zebrafish and other model organisms, but the best strategy for cloning by sequencing has yet to be established. Using four zebrafish inner ear mutants, we developed and compared two approaches for 'cloning by sequencing': one based on bulk segregant linkage (BSFseq) and one based on homozygosity mapping (HMFseq). Using BSFseq we discovered that mutations in lmx1b and jagged1b cause abnormal ear morphogenesis. With HMFseq we validated that the disruption of cdh23 abolishes the ear's sensory functions and identified a candidate lesion in lhfpl5a predicted to cause nonsyndromic deafness. The success of HMFseq shows that the high intrastrain polymorphism rate in zebrafish eliminates the need for time-consuming map crosses. Additionally, we analyzed diversity in zebrafish laboratory strains to find areas of elevated diversity and areas of fixed homozygosity, reinforcing recent findings that genome diversity is clustered. We present a database of >15 million sequence variants that provides much of this approach's power. In our four test cases, only a single candidate single nucleotide polymorphism (SNP) remained after subtracting all database SNPs from a mutant's critical region. The saturation of the common SNP database and our open source analysis pipeline MegaMapper will improve the pace at which the zebrafish community makes unique discoveries relevant to human health.
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http://dx.doi.org/10.1242/dev.083931DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3478692PMC
November 2012

The Usher gene cadherin 23 is expressed in the zebrafish brain and a subset of retinal amacrine cells.

Mol Vis 2012 5;18:2309-22. Epub 2012 Sep 5.

Oregon Hearing Research Center and Vollum Institute, HHMI/Oregon Health & Science University, Portland, OR 97219, USA.

Purpose: To characterize the expression pattern of cadherin 23 (cdh23) in the zebrafish visual system, and to determine whether zebrafish cdh23 mutants have retinal defects similar to those present in the human disease Usher syndrome 1D.

Methods: In situ hybridization and immunohistochemistry were used to characterize cdh23 expression in the zebrafish, and to evaluate cdh23 mutants for retinal degeneration. Visual function was assessed by measurement of the optokinetic response in cdh23 siblings and mutants.

Results: We detected cdh23 mRNA expression in multiple nuclei of both the developing and adult central nervous system. In the retina, cdh23 mRNA was expressed in a small subset of amacrine cells, beginning at 70 h postfertilization and continuing through adulthood. No expression was detected in photoreceptors. The cdh23-positive population of amacrine cells was GABAergic. Examination of homozygous larvae expressing two different mutant alleles of cdh23-cdh23(tc317e) or cdh23(tj264a)-revealed no detectable morphological retinal defects or degeneration. In addition, the optokinetic response to moving gratings of varied contrast or spatial frequency was normal in both mutants.

Conclusions: Unlike in other vertebrates, cdh23 is not detectable in zebrafish photoreceptors. Instead, cdh23 is expressed by a small subset of GABAergic amacrine cells. Moreover, larvae with mutations in cdh23 do not exhibit any signs of gross retinal degeneration or dysfunction. The role played by cdh23 in human retinal function is likely performed by either a different gene or an unidentified cdh23 splice variant in the retina that is not affected by the above mutations.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3441156PMC
January 2013

Kinocilia mediate mechanosensitivity in developing zebrafish hair cells.

Dev Cell 2012 Aug;23(2):329-41

Howard Hughes Medical Institute, Oregon Hearing Research Center, 3181 SW Sam Jackson Park Road, Oregon Health and Science University, Portland, OR 97239, USA.

Mechanosensitive cilia are vital to signaling and development across many species. In sensory hair cells, sound and movement are transduced by apical hair bundles. Each bundle is comprised of a single primary cilium (kinocilium) flanked by multiple rows of actin-filled projections (stereocilia). Extracellular tip links that interconnect stereocilia are thought to gate mechanosensitive channels. In contrast to stereocilia, kinocilia are not critical for hair-cell mechanotransduction. However, by sequentially imaging the structure of hair bundles and mechanosensitivity of individual lateral-line hair cells in vivo, we uncovered a central role for kinocilia in mechanosensation during development. Our data demonstrate that nascent hair cells require kinocilia and kinocilial links for mechanosensitivity. Although nascent hair bundles have correct planar polarity, the polarity of their responses to mechanical stimuli is initially reversed. Later in development, a switch to correctly polarized mechanosensitivity coincides with the formation of tip links and the onset of tip-link-dependent mechanotransduction.
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http://dx.doi.org/10.1016/j.devcel.2012.05.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3426295PMC
August 2012

Rabconnectin3α promotes stable activity of the H+ pump on synaptic vesicles in hair cells.

J Neurosci 2012 Aug;32(32):11144-56

Oregon Hearing Research Center and Vollum Institute, Howard Hughes Medical Institute, Oregon Health and Science University, Portland, Oregon 97239, USA.

Acidification of synaptic vesicles relies on the vacuolar-type ATPase (V-ATPase) and provides the electrochemical driving force for neurotransmitter exchange. The regulatory mechanisms that ensure assembly of the V-ATPase holoenzyme on synaptic vesicles are unknown. Rabconnectin3α (Rbc3α) is a potential candidate for regulation of V-ATPase activity because of its association with synaptic vesicles and its requirement for acidification of intracellular compartments. Here, we provide the first evidence for a role of Rbc3α in synaptic vesicle acidification and neurotransmission. In this study, we characterized mutant alleles of rbc3α isolated from a large-scale screen for zebrafish with auditory/vestibular defects. We show that Rbc3α is localized to basal regions of hair cells in which synaptic vesicles are present. To determine whether Rbc3α regulates V-ATPase activity, we examined the acidification of synaptic vesicles and localization of the V-ATPase in hair cells. In contrast to wild-type hair cells, we observed that synaptic vesicles had elevated pH, and a cytosolic subunit of the V-ATPase was no longer enriched in synaptic regions of mutant hair cells. As a consequence of defective acidification of synaptic vesicles, afferent neurons in rbc3α mutants had reduced firing rates and reduced accuracy of phase-locked action potentials in response to mechanical stimulation of hair cells. Collectively, our data suggest that Rbc3α modulates synaptic transmission in hair cells by promoting V-ATPase activity in synaptic vesicles.
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http://dx.doi.org/10.1523/JNEUROSCI.1705-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3428958PMC
August 2012

Both pre- and postsynaptic activity of Nsf prevents degeneration of hair-cell synapses.

PLoS One 2011 3;6(11):e27146. Epub 2011 Nov 3.

Howard Hughes Medical Institute, Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States of America.

Vesicle fusion contributes to the maintenance of synapses in the nervous system by mediating synaptic transmission, release of neurotrophic factors, and trafficking of membrane receptors. N-ethylmaleimide-sensitive factor (NSF) is indispensible for dissociation of the SNARE-complex following vesicle fusion. Although NSF function has been characterized extensively in vitro, the in vivo role of NSF in vertebrate synaptogenesis is relatively unexplored. Zebrafish possess two nsf genes, nsf and nsfb. Here, we examine the function of either Nsf or Nsfb in the pre- and postsynaptic cells of the zebrafish lateral line organ and demonstrate that Nsf, but not Nsfb, is required for maintenance of afferent synapses in hair cells. In addition to peripheral defects in nsf mutants, neurodegeneration of glutamatergic synapses in the central nervous system also occurs in the absence of Nsf function. Expression of an nsf transgene in a null background indicates that stabilization of synapses requires Nsf function in both hair cells and afferent neurons. To identify potential targets of Nsf-mediated fusion, we examined the expression of genes implicated in stabilizing synapses and found that transcripts for multiple genes including brain-derived neurotrophic factor (bdnf) were significantly reduced in nsf mutants. With regard to trafficking of BDNF, we observed a striking accumulation of BDNF in the neurites of nsf mutant afferent neurons. In addition, injection of recombinant BDNF protein partially rescued the degeneration of afferent synapses in nsf mutants. These results establish a role for Nsf in the maintenance of synaptic contacts between hair cells and afferent neurons, mediated in part via the secretion of trophic signaling factors.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027146PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207842PMC
March 2012

Ribeye is required for presynaptic Ca(V)1.3a channel localization and afferent innervation of sensory hair cells.

Development 2011 Apr 24;138(7):1309-19. Epub 2011 Feb 24.

Howard Hughes Medical Institute, Oregon Hearing Research Center, 3181 SW Sam Jackson Park Road, Oregon Health & Science University, Portland, OR 97239, USA.

Ribbon synapses of the ear, eye and pineal gland contain a unique protein component: Ribeye. Ribeye consists of a novel aggregation domain spliced to the transcription factor CtBP2 and is one of the most abundant proteins in synaptic ribbon bodies. Although the importance of Ribeye for the function and physical integrity of ribbon synapses has been shown, a specific role in synaptogenesis has not been described. Here, we have modulated Ribeye expression in zebrafish hair cells and have examined the role of Ribeye in synapse development. Knockdown of ribeye resulted in fewer stimulus-evoked action potentials from afferent neurons and loss of presynaptic Ca(V)1.3a calcium channel clusters in hair cells. Additionally, afferent innervation of hair cells was reduced in ribeye morphants, and the reduction was correlated with depletion of Ribeye punctae. By contrast, transgenic overexpression of Ribeye resulted in Ca(V)1.3a channels colocalized with ectopic aggregates of Ribeye protein. Overexpression of Ribeye, however, was not sufficient to create ectopic synapses. These findings reveal two distinct functions of Ribeye in ribbon synapse formation--clustering Ca(V)1.3a channels at the presynapse and stabilizing contacts with afferent neurons--and suggest that Ribeye plays an organizing role in synaptogenesis.
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http://dx.doi.org/10.1242/dev.059451DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3050663PMC
April 2011

Mechanism of spontaneous activity in afferent neurons of the zebrafish lateral-line organ.

J Neurosci 2011 Feb;31(5):1614-23

Howard Hughes Medical Institute, Oregon Health and Science University, Portland, Oregon 97239, USA.

Many auditory, vestibular, and lateral-line afferent neurons display spontaneous action potentials. This spontaneous spiking is thought to result from hair-cell glutamate release in the absence of stimuli. Spontaneous release at hair-cell resting potentials presumably results from Ca(V)1.3 L-type calcium channel activity. Here, using intact zebrafish larvae, we recorded robust spontaneous spiking from lateral-line afferent neurons in the absence of external stimuli. Consistent with the above assumptions, spiking was absent in mutants that lacked either Vesicular glutamate transporter 3 (Vglut3) or Ca(V)1.3. We then tested the hypothesis that spontaneous spiking resulted from sustained Ca(V)1.3 activity due to depolarizing currents that are active at rest. Mechanotransduction currents (I(MET)) provide a depolarizing influence to the resting potential. However, following block of I(MET), spontaneous spiking persisted and was characterized by longer interspike intervals and increased periods of inactivity. These results suggest that an additional depolarizing influence maintains the resting potential within the activation range of Ca(V)1.3. To test whether the hyperpolarization-activated cation current, I(h) participates in setting the resting potential, we applied I(h) antagonists. Both ZD7288 and DK-AH 269 reduced spontaneous activity. Finally, concomitant block of I(MET) and I(h) essentially abolished spontaneous activity, ostensibly by hyperpolarization outside of the activation range for Ca(V)1.3. Together, our data support a mechanism for spontaneous spiking that results from Ca(2+)-dependent neurotransmitter release at hair-cell resting potentials that are maintained within the activation range of Ca(V)1.3 channels through active I(MET) and I(h).
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http://dx.doi.org/10.1523/JNEUROSCI.3369-10.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065326PMC
February 2011

Physiological recordings from zebrafish lateral-line hair cells and afferent neurons.

Methods Cell Biol 2010 ;100:219-31

Howard Hughes Medical Institute, Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon, USA.

Sensory signal transduction, the process by which the features of external stimuli are encoded into action potentials, is a complex process that is not fully understood. In fish and amphibia, the lateral-line organ detects water movement and vibration and is critical for schooling behavior and the detection of predators and prey. The lateral-line system in zebrafish serves as an ideal platform to examine encoding of stimuli by sensory hair cells. Here, we describe methods for recording hair-cell microphonics and activity of afferent neurons using intact zebrafish larvae. The recordings are performed by immobilizing and mounting larvae for optimal stimulation of lateral-line hair cells. Hair cells are stimulated with a pressure-controlled water jet and a recording electrode is positioned next to the site of mechanotransduction in order to record microphonics--extracellular voltage changes due to currents through hair-cell mechanotransduction channels. Another readout of the hair-cell activity is obtained by recording action currents from single afferent neurons in response to water-jet stimulation of innervated hair cells. When combined, these techniques make it possible to probe the function of the lateral-line sensory system in an intact zebrafish using controlled, repeatable, physiological stimuli.
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http://dx.doi.org/10.1016/B978-0-12-384892-5.00008-6DOI Listing
February 2011

Quantification of vestibular-induced eye movements in zebrafish larvae.

BMC Neurosci 2010 Sep 3;11:110. Epub 2010 Sep 3.

Howard Hughes Medical Institute, Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.

Background: Vestibular reflexes coordinate movements or sensory input with changes in body or head position. Vestibular-evoked responses that involve the extraocular muscles include the vestibulo-ocular reflex (VOR), a compensatory eye movement to stabilize retinal images. Although an angular VOR attributable to semicircular canal stimulation was reported to be absent in free-swimming zebrafish larvae, recent studies reveal that vestibular-induced eye movements can be evoked in zebrafish larvae by both static tilts and dynamic rotations that tilt the head with respect to gravity.

Results: We have determined herein the basis of sensitivity of the larval eye movements with respect to vestibular stimulus, developmental stage, and sensory receptors of the inner ear. For our experiments, video recordings of larvae rotated sinusoidally at 0.25 Hz were analyzed to quantitate eye movements under infrared illumination. We observed a robust response that appeared as early as 72 hours post fertilization (hpf), which increased in amplitude over time. Unlike rotation about an earth horizontal axis, rotation about an earth vertical axis at 0.25 Hz did not evoke eye movements. Moreover, vestibular-induced responses were absent in mutant cdh23 larvae and larvae lacking anterior otoliths.

Conclusions: Our results provide evidence for a functional vestibulo-oculomotor circuit in 72 hpf zebrafish larvae that relies upon sensory input from anterior/utricular otolith organs.
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http://dx.doi.org/10.1186/1471-2202-11-110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2941499PMC
September 2010

In vivo evidence for transdifferentiation of peripheral neurons.

Development 2010 Sep 4;137(18):3047-56. Epub 2010 Aug 4.

Department of Physiology and Biophysics, Neuroscience Graduate Program and Medical Scientist Training Program, Anschutz Medical Campus, University of Colorado, 12800 East 19th Avenue, Mail Stop 8307, PO Box 6511, Aurora, CO 80045, USA.

It is commonly thought that differentiated neurons do not give rise to new cells, severely limiting the potential for regeneration and repair of the mature nervous system. However, we have identified cells in zebrafish larvae that first differentiate into dorsal root ganglia sensory neurons but later acquire a sympathetic neuron phenotype. These transdifferentiating neurons are present in wild-type zebrafish. However, they are increased in number in larvae that have a mutant voltage-gated sodium channel gene, scn8aa. Sodium channel knock-down promotes migration of differentiated sensory neurons away from the ganglia. Once in a new environment, sensory neurons transdifferentiate regardless of sodium channel expression. These findings reveal an unsuspected plasticity in differentiated neurons that points to new strategies for treatment of nervous system disease.
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http://dx.doi.org/10.1242/dev.052696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2926955PMC
September 2010
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