Publications by authors named "Stephan C Collins"

24 Publications

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A positively-selected MAGEE2 LoF allele is associated with sexual dimorphism in human brain size, and shows similar phenotypes in Magee2 null mice.

Mol Biol Evol 2021 Aug 31. Epub 2021 Aug 31.

Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK.

A nonsense allele at rs1343879 in human MAGEE2 on chromosome X has previously been reported as a strong candidate for positive selection in East Asia. This premature stop codon causing ∼80% protein truncation is characterized by a striking geographical pattern of high population differentiation: common in Asia and the Americas (up to 84% in the 1000 Genomes Project East Asians) but rare elsewhere. Here, we generated a Magee2 mouse knockout mimicking the human loss-of-function mutation to study its functional consequences. The Magee2 null mice did not exhibit gross abnormalities apart from enlarged brain structures (13% increased total brain area, P = 0.0022) in hemizygous males. The area of the granular retrosplenial cortex responsible for memory, navigation and spatial information processing was the most severely affected, exhibiting an enlargement of 34% (P = 3.4x10-6). The brain size in homozygous females showed the opposite trend of reduced brain size, although this did not reach statistical significance. With these insights, we performed human association analyses between brain size measurements and rs1343879 genotypes in 141 Chinese volunteers with brain MRI scans, replicating the sexual dimorphism seen in the knockout mouse model. The derived stop gain allele was significantly associated with a larger volume of grey matter in males (P = 0.00094), and smaller volumes of grey (P = 0.00021) and white (P = 0.0015) matter in females. It is unclear whether or not the observed neuroanatomical phenotypes affect behaviour or cognition, but it might have been the driving force underlying the positive selection in humans.
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http://dx.doi.org/10.1093/molbev/msab243DOI Listing
August 2021

Haploinsufficiency of the HIRA gene located in the 22q11 deletion syndrome region is associated with abnormal neurodevelopment and impaired dendritic outgrowth.

Hum Genet 2021 Jun 8;140(6):885-896. Epub 2021 Jan 8.

Service de Génétique, Centre Hospitalier Régional Universitaire, Tours, France.

The 22q11.2 deletion syndrome (22q11DS) is associated with a wide spectrum of cognitive and psychiatric symptoms. Despite the considerable work performed over the past 20 years, the genetic etiology of the neurodevelopmental phenotype remains speculative. Here, we report de novo heterozygous truncating variants in the HIRA (Histone cell cycle regulation defective, S. Cerevisiae, homolog of, A) gene associated with a neurodevelopmental disorder in two unrelated patients. HIRA is located within the commonly deleted region of the 22q11DS and encodes a histone chaperone that regulates neural progenitor proliferation and neurogenesis, and that belongs to the WD40 Repeat (WDR) protein family involved in brain development and neuronal connectivity. To address the specific impact of HIRA haploinsufficiency in the neurodevelopmental phenotype of 22q11DS, we combined Hira knock-down strategies in developing mouse primary hippocampal neurons, and the direct study of brains from heterozygous Hira mice. Our in vitro analyses revealed that Hira gene is mostly expressed during neuritogenesis and early dendritogenesis stages in mouse total brain and in developing primary hippocampal neurons. Moreover, shRNA knock-down experiments showed that a twofold decrease of endogenous Hira expression level resulted in an impaired dendritic growth and branching in primary developing hippocampal neuronal cultures. In parallel, in vivo analyses demonstrated that Hira mice displayed subtle neuroanatomical defects including a reduced size of the hippocampus, the fornix and the corpus callosum. Our results suggest that HIRA haploinsufficiency would likely contribute to the complex pathophysiology of the neurodevelopmental phenotype of 22q11DS by impairing key processes in neurogenesis and by causing neuroanatomical defects during cerebral development.
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http://dx.doi.org/10.1007/s00439-020-02252-1DOI Listing
June 2021

Heterozygous Variants in KDM4B Lead to Global Developmental Delay and Neuroanatomical Defects.

Am J Hum Genet 2020 12 23;107(6):1170-1177. Epub 2020 Nov 23.

Division of Newborn Medicine, Department of Pediatrics, Boston Children's Hospital, Boston, MA 02115, USA; Division of Genetics and Genomics, Boston Children's Hospital, Boston, MA 02115, USA; The Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA. Electronic address:

KDM4B is a lysine-specific demethylase with a preferential activity on H3K9 tri/di-methylation (H3K9me3/2)-modified histones. H3K9 tri/di-demethylation is an important epigenetic mechanism responsible for silencing of gene expression in animal development and cancer. However, the role of KDM4B on human development is still poorly characterized. Through international data sharing, we gathered a cohort of nine individuals with mono-allelic de novo or inherited variants in KDM4B. All individuals presented with dysmorphic features and global developmental delay (GDD) with language and motor skills most affected. Three individuals had a history of seizures, and four had anomalies on brain imaging ranging from agenesis of the corpus callosum with hydrocephalus to cystic formations, abnormal hippocampi, and polymicrogyria. In mice, lysine demethylase 4B is expressed during brain development with high levels in the hippocampus, a region important for learning and memory. To understand how KDM4B variants can lead to GDD in humans, we assessed the effect of KDM4B disruption on brain anatomy and behavior through an in vivo heterozygous mouse model (Kdm4b), focusing on neuroanatomical changes. In mutant mice, the total brain volume was significantly reduced with decreased size of the hippocampal dentate gyrus, partial agenesis of the corpus callosum, and ventriculomegaly. This report demonstrates that variants in KDM4B are associated with GDD/ intellectual disability and neuroanatomical defects. Our findings suggest that KDM4B variation leads to a chromatinopathy, broadening the spectrum of this group of Mendelian disorders caused by alterations in epigenetic machinery.
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http://dx.doi.org/10.1016/j.ajhg.2020.11.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7820620PMC
December 2020

Large-scale neuroanatomical study uncovers 198 gene associations in mouse brain morphogenesis.

Nat Commun 2019 08 1;10(1):3465. Epub 2019 Aug 1.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67404, Illkirch, France.

Brain morphogenesis is an important process contributing to higher-order cognition, however our knowledge about its biological basis is largely incomplete. Here we analyze 118 neuroanatomical parameters in 1,566 mutant mouse lines and identify 198 genes whose disruptions yield NeuroAnatomical Phenotypes (NAPs), mostly affecting structures implicated in brain connectivity. Groups of functionally similar NAP genes participate in pathways involving the cytoskeleton, the cell cycle and the synapse, display distinct fetal and postnatal brain expression dynamics and importantly, their disruption can yield convergent phenotypic patterns. 17% of human unique orthologues of mouse NAP genes are known loci for cognitive dysfunction. The remaining 83% constitute a vast pool of genes newly implicated in brain architecture, providing the largest study of mouse NAP genes and pathways. This offers a complementary resource to human genetic studies and predict that many more genes could be involved in mammalian brain morphogenesis.
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http://dx.doi.org/10.1038/s41467-019-11431-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6671969PMC
August 2019

The neuroanatomy of Eml1 knockout mice, a model of subcortical heterotopia.

J Anat 2019 09 7;235(3):637-650. Epub 2019 Jun 7.

INSERM UMR S-1270, Paris, France.

The cerebral cortex is a highly organized structure responsible for advanced cognitive functions. Its development relies on a series of steps including neural progenitor cell proliferation, neuronal migration, axonal outgrowth and brain wiring. Disruption of these steps leads to cortical malformations, often associated with intellectual disability and epilepsy. We have generated a new resource to shed further light on subcortical heterotopia, a malformation characterized by abnormal neuronal position. We describe here the generation and characterization of a knockout (KO) mouse model for Eml1, a microtubule-associated protein showing mutations in human ribbon-like subcortical heterotopia. As previously reported for a spontaneous mouse mutant showing a mutation in Eml1, we observe severe cortical heterotopia in the KO. We also observe abnormal progenitor cells in early corticogenesis, likely to be the origin of the defects. EML1 KO mice on the C57BL/6N genetic background also appear to present a wider phenotype than the original mouse mutant, showing additional brain anomalies, such as corpus callosum abnormalities. We compare the anatomy of male and female mice and also study heterozygote animals. This new resource will help unravel roles for Eml1 in brain development and tissue architecture, as well as the mechanisms leading to severe subcortical heterotopia.
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http://dx.doi.org/10.1111/joa.13013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6704242PMC
September 2019

TUBG1 missense variants underlying cortical malformations disrupt neuronal locomotion and microtubule dynamics but not neurogenesis.

Nat Commun 2019 05 13;10(1):2129. Epub 2019 May 13.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400, Illkirch, France.

De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy. Here, we investigated through in-utero electroporation and in-vivo studies, how four of these variants affect cortical development. We show that TUBG1 mutants affect neuronal positioning, disrupting the locomotion of new-born neurons but without affecting progenitors' proliferation. We further demonstrate that pathogenic TUBG1 variants are linked to reduced microtubule dynamics but without major structural nor functional centrosome defects in subject-derived fibroblasts. Additionally, we developed a knock-in Tubg1 mouse model and assessed consequences of the mutation. Although centrosomal positioning in bipolar neurons is correct, they fail to initiate locomotion. Furthermore, Tubg1 animals show neuroanatomical and behavioral defects and increased epileptic cortical activity. We show that Tubg1 mice partially mimic the human phenotype and therefore represent a relevant model for further investigations of the physiopathology of cortical malformations.
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http://dx.doi.org/10.1038/s41467-019-10081-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6513894PMC
May 2019

A Method for Parasagittal Sectioning for Neuroanatomical Quantification of Brain Structures in the Adult Mouse.

Curr Protoc Mouse Biol 2018 Sep 26;8(3):e48. Epub 2018 Jun 26.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

In this article, we present a standardized protocol for fast and robust neuroanatomical phenotyping of the adult mouse brain, which complements a previously published article (doi: 10.1002/cpmo.12) in Current Protocols in Mouse Biology. It is aimed at providing an experimental pipeline within an academic research setting from experimental work to data analysis. Our analysis focuses on one single parasagittal plane, covering the majority of brain regions involved in higher order cognitions such as the cortex, hippocampus, and cerebellum, for a total of 166 parameters of area, length, and cell-level measurements in contrast to 78 parameters in our previously published coronal screen. Benefits of using parasagittal analysis for large-scale neuroanatomic screens are discussed. © 2018 by John Wiley & Sons, Inc.
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http://dx.doi.org/10.1002/cpmo.48DOI Listing
September 2018

Modulation of large dense core vesicle insulin content mediates rhythmic hormone release from pancreatic beta cells over the 24h cycle.

PLoS One 2018 15;13(3):e0193882. Epub 2018 Mar 15.

CSGA, AgroSup Dijon, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université de Bourgogne Franche-Comté, 9E Boulevard Jeanne d'Arc, Dijon, France.

The rhythmic nature of insulin secretion over the 24h cycle in pancreatic islets has been mostly investigated using transcriptomics studies showing that modulation of insulin secretion over this cycle is achieved via distal stages of insulin secretion. We set out to measure β-cell exocytosis using in depth cell physiology techniques at several time points. In agreement with the activity and feeding pattern of nocturnal rodents, we find that C57/Bl6J islets in culture for 24h exhibit higher insulin secretion during the corresponding dark phase than in the light phase (Zeitgeber Time ZT20 and ZT8, respectively, in vivo). Glucose-induced insulin secretion is increased by 21% despite normal intracellular Ca2+ transients and depolarization-evoked exocytosis, as measured by whole-cell capacitance measurements. This paradox is explained by a 1.37-fold increase in beta cell insulin content. Ultramorphological analyses show that vesicle size and density are unaltered, demonstrating that intravesicular insulin content per granule is modulated over the 24h cycle. Proinsulin levels did not change between ZT8 and ZT20. Islet glucagon content was inversely proportional to insulin content indicating that this unique feature is likely to support a physiological role. Microarray data identified the differential expression of 301 transcripts, of which 26 are miRNAs and 54 are known genes (including C2cd4b, a gene previously involved in insulin processing, and clock genes such as Bmal1 and Rev-erbα). Mouse β-cell secretion over the full course of the 24h cycle may rely on several distinct cellular functions but late night increase in insulin secretion depends solely on granule insulin content.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0193882PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5854349PMC
June 2018

WD40-repeat 47, a microtubule-associated protein, is essential for brain development and autophagy.

Proc Natl Acad Sci U S A 2017 10 12;114(44):E9308-E9317. Epub 2017 Oct 12.

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67404 Illkirch, France;

The family of WD40-repeat (WDR) proteins is one of the largest in eukaryotes, but little is known about their function in brain development. Among 26 WDR genes assessed, we found 7 displaying a major impact in neuronal morphology when inactivated in mice. Remarkably, all seven genes showed corpus callosum defects, including thicker (, , , and ), thinner ( and ), or absent corpus callosum (), revealing a common role for WDR genes in brain connectivity. We focused on the poorly studied WDR47 protein sharing structural homology with LIS1, which causes lissencephaly. In a dosage-dependent manner, mice lacking showed lethality, extensive fiber defects, microcephaly, thinner cortices, and sensory motor gating abnormalities. We showed that WDR47 shares functional characteristics with LIS1 and participates in key microtubule-mediated processes, including neural stem cell proliferation, radial migration, and growth cone dynamics. In absence of WDR47, the exhaustion of late cortical progenitors and the consequent decrease of neurogenesis together with the impaired survival of late-born neurons are likely yielding to the worsening of the microcephaly phenotype postnatally. Interestingly, the WDR47-specific C-terminal to LisH (CTLH) domain was associated with functions in autophagy described in mammals. Silencing WDR47 in hypothalamic GT1-7 neuronal cells and yeast models independently recapitulated these findings, showing conserved mechanisms. Finally, our data identified superior cervical ganglion-10 (SCG10) as an interacting partner of WDR47. Taken together, these results provide a starting point for studying the implications of WDR proteins in neuronal regulation of microtubules and autophagy.
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http://dx.doi.org/10.1073/pnas.1713625114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5676932PMC
October 2017

The Immune Signaling Adaptor LAT Contributes to the Neuroanatomical Phenotype of 16p11.2 BP2-BP3 CNVs.

Am J Hum Genet 2017 Oct 28;101(4):564-577. Epub 2017 Sep 28.

Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland. Electronic address:

Copy-number changes in 16p11.2 contribute significantly to neuropsychiatric traits. Besides the 600 kb BP4-BP5 CNV found in 0.5%-1% of individuals with autism spectrum disorders and schizophrenia and whose rearrangement causes reciprocal defects in head size and body weight, a second distal 220 kb BP2-BP3 CNV is likewise a potent driver of neuropsychiatric, anatomical, and metabolic pathologies. These two CNVs are engaged in complex reciprocal chromatin looping, intimating a functional relationship between genes in these regions that might be relevant to pathomechanism. We assessed the drivers of the distal 16p11.2 duplication by overexpressing each of the nine encompassed genes in zebrafish. Only overexpression of LAT induced a reduction of brain proliferating cells and concomitant microcephaly. Consistently, suppression of the zebrafish ortholog induced an increase of proliferation and macrocephaly. These phenotypes were not unique to zebrafish; Lat knockout mice show brain volumetric changes. Consistent with the hypothesis that LAT dosage is relevant to the CNV pathology, we observed similar effects upon overexpression of CD247 and ZAP70, encoding members of the LAT signalosome. We also evaluated whether LAT was interacting with KCTD13, MVP, and MAPK3, major driver and modifiers of the proximal 16p11.2 600 kb BP4-BP5 syndromes, respectively. Co-injected embryos exhibited an increased microcephaly, suggesting the presence of genetic interaction. Correspondingly, carriers of 1.7 Mb BP1-BP5 rearrangements that encompass both the BP2-BP3 and BP4-BP5 loci showed more severe phenotypes. Taken together, our results suggest that LAT, besides its well-recognized function in T cell development, is a major contributor of the 16p11.2 220 kb BP2-BP3 CNV-associated neurodevelopmental phenotypes.
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http://dx.doi.org/10.1016/j.ajhg.2017.08.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5630231PMC
October 2017

Molecular genetics of the transcription factor GLIS3 identifies its dual function in beta cells and neurons.

Genomics 2018 03 11;110(2):98-111. Epub 2017 Sep 11.

Sorbonne Universities, University Pierre & Marie Curie, University Paris Descartes, Sorbonne Paris Cité, INSERM UMR_S1138, Cordeliers Research Centre, Paris, France; The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom; McGill University and Genome Quebec Innovation Centre, 740 Doctor Penfield Avenue, Montreal, QC H3A 0G1, Canada. Electronic address:

The GLIS family zinc finger 3 isoform (GLIS3) is a risk gene for Type 1 and Type 2 diabetes, glaucoma and Alzheimer's disease endophenotype. We identified GLIS3 binding sites in insulin secreting cells (INS1) (FDR q<0.05; enrichment range 1.40-9.11 fold) sharing the motif wrGTTCCCArTAGs, which were enriched in genes involved in neuronal function and autophagy and in risk genes for metabolic and neuro-behavioural diseases. We confirmed experimentally Glis3-mediated regulation of the expression of genes involved in autophagy and neuron function in INS1 and neuronal PC12 cells. Naturally-occurring coding polymorphisms in Glis3 in the Goto-Kakizaki rat model of type 2 diabetes were associated with increased insulin production in vitro and in vivo, suggestive alteration of autophagy in PC12 and INS1 and abnormal neurogenesis in hippocampus neurons. Our results support biological pleiotropy of GLIS3 in pathologies affecting β-cells and neurons and underline the existence of trans‑nosology pathways in diabetes and its co-morbidities.
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http://dx.doi.org/10.1016/j.ygeno.2017.09.001DOI Listing
March 2018

Topological analysis of metabolic networks integrating co-segregating transcriptomes and metabolomes in type 2 diabetic rat congenic series.

Genome Med 2016 09 30;8(1):101. Epub 2016 Sep 30.

Division of Computational and Systems Medicine, Department of Surgery and Cancer, Faculty of Medicine, Sir Alexander Fleming Building, Imperial College, London, SW7 2AZ, UK.

Background: The genetic regulation of metabolic phenotypes (i.e., metabotypes) in type 2 diabetes mellitus occurs through complex organ-specific cellular mechanisms and networks contributing to impaired insulin secretion and insulin resistance. Genome-wide gene expression profiling systems can dissect the genetic contributions to metabolome and transcriptome regulations. The integrative analysis of multiple gene expression traits and metabolic phenotypes (i.e., metabotypes) together with their underlying genetic regulation remains a challenge. Here, we introduce a systems genetics approach based on the topological analysis of a combined molecular network made of genes and metabolites identified through expression and metabotype quantitative trait locus mapping (i.e., eQTL and mQTL) to prioritise biological characterisation of candidate genes and traits.

Methods: We used systematic metabotyping by H NMR spectroscopy and genome-wide gene expression in white adipose tissue to map molecular phenotypes to genomic blocks associated with obesity and insulin secretion in a series of rat congenic strains derived from spontaneously diabetic Goto-Kakizaki (GK) and normoglycemic Brown-Norway (BN) rats. We implemented a network biology strategy approach to visualize the shortest paths between metabolites and genes significantly associated with each genomic block.

Results: Despite strong genomic similarities (95-99 %) among congenics, each strain exhibited specific patterns of gene expression and metabotypes, reflecting the metabolic consequences of series of linked genetic polymorphisms in the congenic intervals. We subsequently used the congenic panel to map quantitative trait loci underlying specific mQTLs and genome-wide eQTLs. Variation in key metabolites like glucose, succinate, lactate, or 3-hydroxybutyrate and second messenger precursors like inositol was associated with several independent genomic intervals, indicating functional redundancy in these regions. To navigate through the complexity of these association networks we mapped candidate genes and metabolites onto metabolic pathways and implemented a shortest path strategy to highlight potential mechanistic links between metabolites and transcripts at colocalized mQTLs and eQTLs. Minimizing the shortest path length drove prioritization of biological validations by gene silencing.

Conclusions: These results underline the importance of network-based integration of multilevel systems genetics datasets to improve understanding of the genetic architecture of metabotype and transcriptomic regulation and to characterize novel functional roles for genes determining tissue-specific metabolism.
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http://dx.doi.org/10.1186/s13073-016-0352-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5045612PMC
September 2016

Transcriptome Profiling in Rat Inbred Strains and Experimental Cross Reveals Discrepant Genetic Architecture of Genome-Wide Gene Expression.

G3 (Bethesda) 2016 Nov 8;6(11):3671-3683. Epub 2016 Nov 8.

The Wellcome Trust Centre for Human Genetics, University of Oxford, OX3 7BN, United Kingdom

To test the impact of genetic heterogeneity on - and -mediated mechanisms of gene expression regulation, we profiled the transcriptome of adipose tissue in 20 inbred congenic strains derived from diabetic Goto-Kakizaki (GK) rats and Brown-Norway (BN) controls, which contain well-defined blocks (1-183 Mb) of genetic polymorphisms, and in 123 genetically heterogeneous rats of an (GK × BN)F2 offspring. Within each congenic we identified 73-1351 differentially expressed genes (DEGs), only 7.7% of which mapped within the congenic blocks, and which may be regulated in The remainder localized outside the blocks, and therefore must be regulated in Most -regulated genes exhibited approximately twofold expression changes, consistent with monoallelic expression. Altered biological pathways were replicated between congenic strains sharing blocks of genetic polymorphisms, but polymorphisms at different loci also had redundant effects on transcription of common distant genes and pathways. We mapped 2735 expression quantitative trait loci (eQTL) in the F2 cross, including 26% predominantly -regulated genes, which validated DEGs in congenic strains. A hotspot of >300 eQTL in a 10 cM region of chromosome 1 was enriched in DEGs in a congenic strain. However, many DEGs among GK, BN and congenic strains did not replicate as eQTL in F2 hybrids, demonstrating distinct mechanisms of gene expression when alleles segregate in an outbred population or are fixed homozygous across the entire genome or in short genomic regions. Our analysis provides conceptual advances in our understanding of the complex architecture of genome expression and pathway regulation, and suggests a prominent impact of epistasis and monoallelic expression on gene transcription.
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http://dx.doi.org/10.1534/g3.116.033274DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5100866PMC
November 2016

Increased Expression of the Diabetes Gene SOX4 Reduces Insulin Secretion by Impaired Fusion Pore Expansion.

Diabetes 2016 07 18;65(7):1952-61. Epub 2016 Mar 18.

Oxford Centre for Diabetes, Endocrinology & Metabolism, Radcliffe Department of Medicine, Oxford, U.K. Department of Neuroscience and Physiology, University of Göteborg, Göteborg, Sweden Oxford National Institute of Health Research, Biomedical Research Centre, Churchill Hospital, Oxford, U.K.

The transcription factor Sox4 has been proposed to underlie the increased type 2 diabetes risk linked to an intronic single nucleotide polymorphism in CDKAL1 In a mouse model expressing a mutant form of Sox4, glucose-induced insulin secretion is reduced by 40% despite normal intracellular Ca(2+) signaling and depolarization-evoked exocytosis. This paradox is explained by a fourfold increase in kiss-and-run exocytosis (as determined by single-granule exocytosis measurements) in which the fusion pore connecting the granule lumen to the exterior expands to a diameter of only 2 nm, which does not allow the exit of insulin. Microarray analysis indicated that this correlated with an increased expression of the exocytosis-regulating protein Stxbp6. In a large collection of human islet preparations (n = 63), STXBP6 expression and glucose-induced insulin secretion correlated positively and negatively with SOX4 expression, respectively. Overexpression of SOX4 in the human insulin-secreting cell EndoC-βH2 interfered with granule emptying and inhibited hormone release, the latter effect reversed by silencing STXBP6 These data suggest that increased SOX4 expression inhibits insulin secretion and increased diabetes risk by the upregulation of STXBP6 and an increase in kiss-and-run exocytosis at the expense of full fusion. We propose that pharmacological interventions promoting fusion pore expansion may be effective in diabetes therapy.
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http://dx.doi.org/10.2337/db15-1489DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4996324PMC
July 2016

Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) and Endolysosomal Two-pore Channels Modulate Membrane Excitability and Stimulus-Secretion Coupling in Mouse Pancreatic β Cells.

J Biol Chem 2015 Aug 7;290(35):21376-92. Epub 2015 Jul 7.

From the Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, United Kingdom,

Pancreatic β cells are electrically excitable and respond to elevated glucose concentrations with bursts of Ca(2+) action potentials due to the activation of voltage-dependent Ca(2+) channels (VDCCs), which leads to the exocytosis of insulin granules. We have examined the possible role of nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca(2+) release from intracellular stores during stimulus-secretion coupling in primary mouse pancreatic β cells. NAADP-regulated Ca(2+) release channels, likely two-pore channels (TPCs), have recently been shown to be a major mechanism for mobilizing Ca(2+) from the endolysosomal system, resulting in localized Ca(2+) signals. We show here that NAADP-mediated Ca(2+) release from endolysosomal Ca(2+) stores activates inward membrane currents and depolarizes the β cell to the threshold for VDCC activation and thereby contributes to glucose-evoked depolarization of the membrane potential during stimulus-response coupling. Selective pharmacological inhibition of NAADP-evoked Ca(2+) release or genetic ablation of endolysosomal TPC1 or TPC2 channels attenuates glucose- and sulfonylurea-induced membrane currents, depolarization, cytoplasmic Ca(2+) signals, and insulin secretion. Our findings implicate NAADP-evoked Ca(2+) release from acidic Ca(2+) storage organelles in stimulus-secretion coupling in β cells.
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http://dx.doi.org/10.1074/jbc.M115.671248DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571866PMC
August 2015

Alteration of hypothalamic glucose and lactate sensing in 48h hyperglycemic rats.

Neurosci Lett 2013 Feb 29;534:75-9. Epub 2012 Nov 29.

CNRS, UMR 6265, CSGA, F-21000 Dijon, France; INRA, UMR1324, CSGA, F-21000 Dijon, France; Université de bourgogne, CSGA, F-21000 Dijon, France.

Hypothalamic detection of nutrients is involved in the control of energy metabolism and is altered in metabolic disorders. Although hypothalamic detection of blood lactate lowers hepatic glucose production and food intake, it is unknown whether it also modulates insulin secretion. To address this, a lactate injection via the right carotid artery (cephalad) was performed in Wistar rats. This triggered a transient increase in insulin secretion. Rats made hyperglycemic for 48h exhibited prolonged insulin secretion in response to a glucose injection via the carotid artery, but lactate injection induced two types of responses: half of the HG rats showed no difference compared to controls and the other half had markedly decreased insulin secretion. Astroglial monocarboxylates transporters MCT1 and MCT4 isoforms transfer lactate from blood to astrocytes and release lactate to the extracellular space, whilst the neuronal MCT2 isoform permits neuronal lactate uptake. We found that astroglial MCT1 and MCT4, and neuronal MCT2 protein levels in the medio-basal hypothalamus (MBH) were not modified by 48h-hyperglycemia. Together, these results indicate that hypothalamic sensing of circulating lactate triggers insulin secretion. Both glucose and lactate sensing are altered in a model of hyperglycemia, without alteration of MBH MCTs protein levels.
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http://dx.doi.org/10.1016/j.neulet.2012.11.033DOI Listing
February 2013

Progression of diet-induced diabetes in C57BL6J mice involves functional dissociation of Ca2(+) channels from secretory vesicles.

Diabetes 2010 May 11;59(5):1192-201. Epub 2010 Feb 11.

Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK.

Objective: The aim of the study was to elucidate the cellular mechanism underlying the suppression of glucose-induced insulin secretion in mice fed a high-fat diet (HFD) for 15 weeks.

Research Design And Methods: C57BL6J mice were fed a HFD or a normal diet (ND) for 3 or 15 weeks. Plasma insulin and glucose levels in vivo were assessed by intraperitoneal glucose tolerance test. Insulin secretion in vitro was studied using static incubations and a perfused pancreas preparation. Membrane currents, electrical activity, and exocytosis were examined by patch-clamp technique measurements. Intracellular calcium concentration ([Ca(2+)](i)) was measured by microfluorimetry. Total internal reflection fluorescence microscope (TIRFM) was used for optical imaging of exocytosis and submembrane depolarization-evoked [Ca(2+)](i). The functional data were complemented by analyses of histology and gene transcription.

Results: After 15 weeks, but not 3 weeks, mice on HFD exhibited hyperglycemia and hypoinsulinemia. Pancreatic islet content and beta-cell area increased 2- and 1.5-fold, respectively. These changes correlated with a 20-50% reduction of glucose-induced insulin secretion (normalized to insulin content). The latter effect was not associated with impaired electrical activity or [Ca(2+)](i) signaling. Single-cell capacitance and TIRFM measurements of exocytosis revealed a selective suppression (>70%) of exocytosis elicited by short (50 ms) depolarization, whereas the responses to longer depolarizations were (500 ms) less affected. The loss of rapid exocytosis correlated with dispersion of Ca(2+) entry in HFD beta-cells. No changes in gene transcription of key exocytotic protein were observed.

Conclusions: HFD results in reduced insulin secretion by causing the functional dissociation of voltage-gated Ca(2+) entry from exocytosis. These observations suggest a novel explanation to the well-established link between obesity and diabetes.
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http://dx.doi.org/10.2337/db09-0791DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857899PMC
May 2010

Suppression of sulfonylurea- and glucose-induced insulin secretion in vitro and in vivo in mice lacking the chloride transport protein ClC-3.

Cell Metab 2009 Oct;10(4):309-15

Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, Malmö, SE-205 02 Malmö, Sweden.

Priming of insulin secretory granules for release requires intragranular acidification and depends on vesicular Cl(-)-fluxes, but the identity of the chloride transporter/ion channel involved is unknown. We tested the hypothesis that the chloride transport protein ClC-3 fulfills these actions in pancreatic beta cells. In ClC-3(-/-) mice, insulin secretion evoked by membrane depolarization (high extracellular K(+), sulfonylureas), or glucose was >60% reduced compared to WT animals. This effect was mirrored by a approximately 80% reduction in depolarization-evoked beta cell exocytosis (monitored as increases in cell capacitance) in single ClC-3(-/-) beta cells, as well as a 44% reduction in proton transport across the granule membrane. ClC-3 expression in the insulin granule was demonstrated by immunoblotting, immunostaining, and negative immuno-EM in a high-purification fraction of large dense-core vesicles (LDCVs) obtained by phogrin-EGFP labeling. The data establish the importance of granular Cl(-) fluxes in granule priming and provide direct evidence for the involvement of ClC-3 in the process.
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http://dx.doi.org/10.1016/j.cmet.2009.08.011DOI Listing
October 2009

Pathophysiological, genetic and gene expression features of a novel rodent model of the cardio-metabolic syndrome.

PLoS One 2008 Aug 13;3(8):e2962. Epub 2008 Aug 13.

The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.

Background: Complex etiology and pathogenesis of pathophysiological components of the cardio-metabolic syndrome have been demonstrated in humans and animal models.

Methodology/principal Findings: We have generated extensive physiological, genetic and genome-wide gene expression profiles in a congenic strain of the spontaneously diabetic Goto-Kakizaki (GK) rat containing a large region (110 cM, 170 Mb) of rat chromosome 1 (RNO1), which covers diabetes and obesity quantitative trait loci (QTL), introgressed onto the genetic background of the normoglycaemic Brown Norway (BN) strain. This novel disease model, which by the length of the congenic region closely mirrors the situation of a chromosome substitution strain, exhibits a wide range of abnormalities directly relevant to components of the cardio-metabolic syndrome and diabetes complications, including hyperglycaemia, hyperinsulinaemia, enhanced insulin secretion both in vivo and in vitro, insulin resistance, hypertriglyceridemia and altered pancreatic and renal histological structures. Gene transcription data in kidney, liver, skeletal muscle and white adipose tissue indicate that a disproportionately high number (43-83%) of genes differentially expressed between congenic and BN rats map to the GK genomic interval targeted in the congenic strain, which represents less than 5% of the total length of the rat genome. Genotype analysis of single nucleotide polymorphisms (SNPs) in strains genetically related to the GK highlights clusters of conserved and strain-specific variants in RNO1 that can assist the identification of naturally occurring variants isolated in diabetic and hypertensive strains when different phenotype selection procedures were applied.

Conclusions: Our results emphasize the importance of rat congenic models for defining the impact of genetic variants in well-characterised QTL regions on in vivo pathophysiological features and cis-/trans- regulation of gene expression. The congenic strain reported here provides a novel and sustainable model for investigating the pathogenesis and genetic basis of risks factors for the cardio-metabolic syndrome.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0002962PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2500170PMC
August 2008

Pancreatic ectopic fat is characterized by adipocyte infiltration and altered lipid composition.

Obesity (Silver Spring) 2008 Mar 17;16(3):522-30. Epub 2008 Jan 17.

Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, UK.

Objective: Sustained exposure to lipids is deleterious for pancreatic islet function. This could be mediated through increased pancreatic fat following increased dietary fat and in obesity, which has implications for the onset of type 2 diabetes. The aims of this study were to determine changes in extent and composition of pancreatic, hepatic, and visceral fat in mice fed a high-fat diet (HFD, 40% by weight) compared with a control diet (5% fat) of similar fatty acid composition, and to compare composition and extent of pancreatic fat in human type 2 diabetes.

Methods And Procedures: Mice were fed HFD for 3 or 15 weeks. Human postmortem pancreas was examined from subjects with type 2 diabetes (n = 9) and controls (n = 7). Tissue lipid content and composition were determined by gas chromatography and pancreatic adipocyte infiltration quantified by morphometry.

Results: Pancreatic triacylglycerol (TG) content was 20x greater (P < 0.05) in HFD mice and there were more pancreatic perilipin-positive adipocytes compared with controls after 15 weeks. The proportions of 18:1n -9 and 18:2n -6 in pancreatic TG and the 20:4n -6/18:2n -6 ratio in phospholipids, were higher (both P < 0.05) after HFD compared with controls. Human pancreatic TG content was correlated with the proportion of pancreatic perilipin-positive adipocytes (r = 0.64, P < 0.05) and associated with unsaturated fatty acid enrichment (P < 0.05).

Discussion: Adipocyte infiltration in pancreatic exocrine tissue is associated with high-fat feeding in mice and pancreatic TG content in humans. This alters the fatty acid milieu of the islet which could contribute to islet dysfunction.
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http://dx.doi.org/10.1038/oby.2007.110DOI Listing
March 2008

Mapping diabetes QTL in an intercross derived from a congenic strain of the Brown Norway and Goto-Kakizaki rats.

Mamm Genome 2006 Jun 12;17(6):538-47. Epub 2006 Jun 12.

The Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Headington, Oxford OX3 7BN, UK.

Genetic studies in experimental crosses derived from the inbred Goto-Kakizaki (GK) rat model of spontaneous diabetes mellitus have identified quantitative trait loci (QTL) for diabetes phenotypes in a large region of rat Chromosome (RNO) 1. To test the impact of GK variants on QTL statistical and biological features, we combined genetic and physiologic studies in a cohort of F(2) hybrids derived from a QTL substitution congenic strain (QTLSCS) carrying a 110-cM GK haplotype of RNO1 introgressed onto the genetic background of the Brown Norway (BN) strain. Glucose intolerance and altered insulin secretion in QTLSCS rats when compared with BN controls were consistent with original QTL features in a GK x BN F(2) cross. Segregating GK alleles in the QTLSCS F(2) cross account for most of these phenotypic differences between QTLSCS and BN rats. However, significant QTL for diabetes traits in both the QTLSCS and GK x BN F(2) cohorts account for a similar small proportion of their variance. Comparing results from these experimental systems provides indirect estimates of the contribution of genetic interactions and environmental factors to QTL architecture as well as locus and biological targets for future post-QTL mapping studies in congenic substrains.
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http://dx.doi.org/10.1007/s00335-005-0168-yDOI Listing
June 2006

Quantitative trait locus dissection in congenic strains of the Goto-Kakizaki rat identifies a region conserved with diabetes loci in human chromosome 1q.

Physiol Genomics 2004 Sep 20;19(1):1-10. Epub 2004 Jul 20.

The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.

Genetic studies in human populations and rodent models have identified regions of human chromosome 1q21-25 and rat chromosome 2 showing evidence of significant and replicated linkage to diabetes-related phenotypes. To investigate the relationship between the human and rat diabetes loci, we fine mapped the rat locus Nidd/gk2 linked to hyperinsulinemia in an F2 cross derived from the diabetic (type 2) Goto-Kakizaki (GK) rat and the Brown Norway (BN) control rat, and carried out its genetic and pathophysiological characterization in BN.GK congenic strains. Evidence of glucose intolerance and enhanced insulin secretion in a congenic strain allowed us to localize the underlying diabetes gene(s) in a rat chromosomal interval of approximately 3-6 cM conserved with an 11-Mb region of human 1q21-23. Positional diabetes candidate genes were tested for transcriptional changes between congenics and controls and sequence variations in a panel of inbred rat strains. Congenic strains of the GK rats represent powerful novel models for accurately defining the pathophysiological impact of diabetes gene(s) at the locus Nidd/gk2 and improving functional annotations of diabetes candidates in human 1q21-23.
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http://dx.doi.org/10.1152/physiolgenomics.00114.2004DOI Listing
September 2004

Marker-assisted congenic screening (MACS): a database tool for the efficient production and characterization of congenic lines.

Mamm Genome 2003 May;14(5):350-6

Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Headington, Oxford, OX3 7BN, UK.

Over the past decades, genetic studies in rodent models of human multifactorial disorders have led to the detection of numerous chromosomal regions associated with disease phenotypes. Owing to the complex control of these phenotypes and the size of the disease loci, identifying the underlying genes requires further analyses in new original models, including chromosome substitution (consomic) and congenic lines, derived to evaluate the phenotypic effects of disease susceptibility loci and fine-map the disease genes. We have developed a relational database (MACS) specifically designed for the genetic marker-assisted production of large series of rodent consomic and congenic lines ("speed congenics"), the organization of their genetic and phenotypic characterizations, and the acquisition and archiving of both genetic and phenotypic data. This database, originally optimized for the production of rat congenics, can also be applied to mouse mapping projects. MACS represents an essential system for significantly improving efficiency and accuracy in investigations of multiple consomic and congenic lines simultaneously derived for different disease loci, and ultimately cloning genes underlying complex phenotypes.
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http://dx.doi.org/10.1007/s00335-002-3058-6DOI Listing
May 2003
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