Publications by authors named "Sara Majello"

4 Publications

  • Page 1 of 1

Strategies for genetic inactivation of long noncoding RNAs in zebrafish.

RNA 2019 08 1;25(8):897-904. Epub 2019 May 1.

Institut Curie, PSL Research University, CNRS UMR3215, INSERM U934, 75005 Paris, France.

The number of annotated long noncoding RNAs (lncRNAs) continues to grow; however, their functional characterization in model organisms has been hampered by the lack of reliable genetic inactivation strategies. While partial or full deletions of lncRNA loci disrupt lncRNA expression, they do not permit the formal association of a phenotype with the encoded transcript. Here, we examined several alternative strategies for generating lncRNA null alleles in zebrafish and found that they often resulted in unpredicted changes to lncRNA expression. Removal of the transcription start sites (TSSs) of lncRNA genes resulted in hypomorphic mutants, due to the usage of either constitutive or tissue-specific alternative TSSs. Deletions of short, highly conserved lncRNA regions can also lead to overexpression of truncated transcripts. In contrast, knock-in of a polyadenylation signal enabled complete inactivation of , the most abundant vertebrate lncRNA. In summary, lncRNA null alleles require extensive in vivo validation, and we propose insertion of transcription termination sequences as the most reliable approach to generate lncRNA-deficient zebrafish.
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http://dx.doi.org/10.1261/rna.069484.118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6633201PMC
August 2019

Anisotropic organization of circumferential actomyosin characterizes hematopoietic stem cells emergence in the zebrafish.

Elife 2018 08 22;7. Epub 2018 Aug 22.

Department of Developmental and Stem Cell Biology, Institut Pasteur, Paris, France.

Hematopoiesis leads to the formation of blood and immune cells. Hematopoietic stem cells emerge during development, from vascular components, via a process called the endothelial-to-hematopoietic transition (EHT). Here, we reveal essential biomechanical features of the EHT, using the zebrafish embryo imaged at unprecedented spatio-temporal resolution and an algorithm to unwrap the aorta into 2D-cartography. We show that the transition involves anisotropic contraction along the antero-posterior axis, with heterogenous organization of contractile circumferential actomyosin. The biomechanics of the contraction is oscillatory, with unusually long periods in comparison to other apical constriction mechanisms described so far in morphogenesis, and is supported by the anisotropic reinforcement of junctional contacts. Finally, we show that abrogation of blood flow impairs the actin cytoskeleton, the morphodynamics of EHT cells, and the orientation of the emergence. Overall, our results underline the peculiarities of the EHT biomechanics and the influence of the mechanical forces exerted by blood flow.
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http://dx.doi.org/10.7554/eLife.37355DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6105311PMC
August 2018

Comparative analyses of super-enhancers reveal conserved elements in vertebrate genomes.

Genome Res 2017 02 13;27(2):259-268. Epub 2016 Dec 13.

Institut Curie, PSL Research University, INSERM U934, CNRS UMR 3215, F-75005, Paris, France.

Super-enhancers (SEs) are key transcriptional drivers of cellular, developmental, and disease states in mammals, yet the conservational and regulatory features of these enhancer elements in nonmammalian vertebrates are unknown. To define SEs in zebrafish and enable sequence and functional comparisons to mouse and human SEs, we used genome-wide histone H3 lysine 27 acetylation (H3K27ac) occupancy as a primary SE delineator. Our study determined the set of SEs in pluripotent state cells and adult zebrafish tissues and revealed both similarities and differences between zebrafish and mammalian SEs. Although the total number of SEs was proportional to the genome size, the genomic distribution of zebrafish SEs differed from that of the mammalian SEs. Despite the evolutionary distance separating zebrafish and mammals and the low overall SE sequence conservation, ∼42% of zebrafish SEs were located in close proximity to orthologs that also were associated with SEs in mouse and human. Compared to their nonassociated counterparts, higher sequence conservation was revealed for those SEs that have maintained orthologous gene associations. Functional dissection of two of these SEs identified conserved sequence elements and tissue-specific expression patterns, while chromatin accessibility analyses predicted transcription factors governing the function of pluripotent state zebrafish SEs. Our zebrafish annotations and comparative studies show the extent of SE usage and their conservation across vertebrates, permitting future gene regulatory studies in several tissues.
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http://dx.doi.org/10.1101/gr.203679.115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5287231PMC
February 2017