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Developmental and comparative transcriptomic identification of iridophore contribution to white barring in clownfish.

Author(s) : Salis P, Lorin T, Lewis V, Rey C, Marcionetti A, Escande M, Roux N, Besseau L, Salamin N, Semon M, Parichy D, Volff J, Laudet V,
Journal : Pigment Cell Melanoma Res
Actinopterygian fishes harbor at least eight distinct pigment cell types, leading to a fascinating diversity of colors. Among this diversity, the cellular origin of the white color appears to be linked to several pigment cell types such as iridophores or leucophores. We used the clownfish Amphiprion ocellaris, which has a color pattern consisting of white bars over a darker body, to characterize thepigment cells that underlie the white hue. We observe by electron microscopy that cells in white bars are similar to iridophores. In addition, the transcriptomic signature of clownfish white bars exhibits similarities with that of zebrafish iridophores. We further show by pharmacological treatments that these cells are necessary for the white color. Among the top differentially expressed genes in white skin, we identified several genes (fhl2a, fhl2b, saiyan, gpnmb, and apoD1a) and show that three of them are expressed in iridophores. Finally, we show by CRISPR/Cas9 mutagenesis that these genes are critical for iridophore developmentin zebrafish. Our analyses provide clues to the genomic underpinning of color diversity and allow identification of new iridophore genes in fish.

Genome editing in primary cells and in vivo using viral-derived Nanoblades loaded with Cas9-sgRNA ribonucleoproteins.

Author(s) : Mangeot P, Risson V, Fusil F, Marnef A, Laurent E, Blin J, Mournetas V, Massourides E, Sohier T, Corbin A, Aube F, Teixeira M, Pinset C, Schaeffer L, Legube G, Cosset F, Verhoeyen E, Ohlmann T, Ricci E,
Journal : Nat Commun
Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cellscan be technically challenging when working with primary cells or in vivo. Here,we use engineered murine leukemia virus-like particles loaded with Cas9-sgRNA ribonucleoproteins (Nanoblades) to induce efficient genome-editing in cell linesand primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades are also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for "all-in-one" homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process issimple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.

Males as somatic investment in a parthenogenetic nematode.

Author(s) : Grosmaire M, Launay C, Siegwald M, Brugiere T, Estrada-Virrueta L, Berger D, Burny C, Modolo L, Blaxter M, Meister P, Felix M, Gouyon P, Delattre M,
Journal : Science
We report the reproductive strategy of the nematode Mesorhabditis belari This species produces only 9% males, whose sperm is necessary to fertilize and activate the eggs. However, most of the fertilized eggs develop without using the sperm DNA and produce female individuals. Only in 9% of eggs is the male DNA utilized, producing sons. We found that mixing of parental genomes only gives rise to males because the Y-bearing sperm of males are much more competent than the X-bearing sperm for penetrating the eggs. In this previously unrecognized strategy, asexual females produce few sexual males whose genes never reenter thefemale pool. Here, production of males is of interest only if sons are more likely to mate with their sisters. Using game theory, we show that in this context, the production of 9% males by M. belari females is an evolutionary stable strategy.

Modeling Edar expression reveals the hidden dynamics of tooth signaling center patterning

Author(s) : Sadier A, Twarogowska M, Steklíková k, Hayden L, Lambert A, Schneider P, Laudet V, Hovorakova M, Calvez V, Pantalacci S,
Journal : PLOS Biology

Single cell RNA-seq identifies the origins of heterogeneity in efficient cell transdifferentiation and reprogramming

Author(s) : Francesconi M, Di Stefano B, Berenguer C, de Andrés-Aguayo L, Plana-Carmona M, Mendez-Lago M, Guillaumet-Adkins A, Rodriguez-Esteban G, Gut M, Gut I, Heyn H, Lehner B, Graf T,
Journal : eLife

System-wide Profiling of RNA-Binding Proteins Uncovers Key Regulators of Virus Infection.

Author(s) : Garcia-Moreno M, Noerenberg M, Ni S, Jarvelin A, Gonzalez-Almela E, Lenz C, Bach-Pages M, Cox V, Avolio R, Davis T, Hester S, Sohier T, Li B, Heikel G, Michlewski G, Sanz M, Carrasco L, Ricci E, Pelechano V, Davis I, Fischer B, Mohammed S, Castello A,
Journal : Mol Cell
The compendium of RNA-binding proteins (RBPs) has been greatly expanded by the development of RNA-interactome capture (RIC). However, it remained unknown if the complement of RBPs changes in response to environmental perturbations and whether these rearrangements are important. To answer these questions, we developed "comparative RIC" and applied it to cells challenged with an RNA virus called sindbis (SINV). Over 200 RBPs display differential interaction with RNA upon SINV infection. These alterations are mainly driven by the loss of cellular mRNAs andthe emergence of viral RNA. RBPs stimulated by the infection redistribute to viral replication factories and regulate the capacity of the virus to infect. For example, ablation of XRN1 causes cells to be refractory to SINV, while GEMIN5 moonlights as a regulator of SINV gene expression. In summary, RNA availability controls RBP localization and function in SINV-infected cells.

The extruded non-template strand determines the architecture of R-loops.

Author(s) : Carrasco-Salas Y, Malapert A, Sulthana S, Molcrette B, Chazot-Franguiadakis L, Bernard P, Chedin F, Faivre-Moskalenko C, Vanoosthuyse V,
Journal : Nucleic Acids Res
Three-stranded R-loop structures have been associated with genomic instability phenotypes. What underlies their wide-ranging effects on genome stability remains poorly understood. Here we combined biochemical and atomic force microscopy approaches with single molecule R-loop footprinting to demonstrate that R-loops formed at the model Airn locus in vitro adopt a defined set of three-dimensionalconformations characterized by distinct shapes and volumes, which we call R-loopobjects. Interestingly, we show that these R-loop objects impose specific physical constraints on the DNA, as revealed by the presence of stereotypical angles in the surrounding DNA. Biochemical probing and mutagenesis experiments revealed that the formation of R-loop objects at Airn is dictated by the extruded non-template strand, suggesting that R-loops possess intrinsic sequence-driven properties. Consistent with this, we show that R-loops formed at the fission yeast gene sum3 do not form detectable R-loop objects. Our results reveal that R-loops differ by their architectures and that the organization of the non-template strand is a fundamental characteristic of R-loops, which could explain that only a subset of R-loops is associated with replication-dependent DNA breaks.