Project description:Background Sex chromosomes are subject to evolutionary pressures distinct from the remainder of the genome, shaping their structure and sequence content. We are interested in the sex chromosomes of domestic pigs (Sus scrofa), how their structure and gene content compares and contrasts with other mammalian species, and the role of gonosomal genes in fertility. This requires an understanding of the XY-homologous sequence on these chromosomes. To this end, we performed microarray-based comparative genomic hybridisation (array-CGH) with male and female Duroc genomic DNA on a pig X-chromosome BAC tiling-path microarray. Putative XY-homologous BACs from regions of interest were subsequently FISH mapped. Results We show that the porcine PAR is approximately 6.5-6.9Mb at the beginning of the short arm of the X, with gene content reflective of the artiodactyl common ancestor. Our array-CGH data also shows an XY-homologous region close to the end of the X long arm, spanning three X BACs. These BACs were FISH mapped, and paint the entire long arm of SSCY. Further clones of interest revealed X-autosomal homology or regions containing repetitive content. Conclusions This study has identified regions of XY homology in the pig genome, and defined the boundary of the PAR on the X chromosome. This adds to our understanding of the evolution of the sex chromosomes in different mammalian lineages, and will prove valuable for future comparative genomic work in suids and for the construction and annotation of the genome sequence for the sex chromosomes. Our finding that the SSCYq repetitive content has corresponding sequence on the X chromosome gives further insight into structure of SSCY, and suggests further functionally important sequences remain to be discovered on the X and Y.
Project description:We present evidence implicating the BAF (BRG1/BRM Associated Factor) chromatin remodeler in meiotic sex chromosome inactivation (MSCI). By immunofluorescence (IF), the putative BAF DNA binding subunit, ARID1A (AT-rich Interaction Domain 1a), appeared enriched on the male sex chromosomes during diplonema of meiosis I. The germ cell-specific depletion of ARID1A resulted in a pachynema arrest and failure to repress sex-linked genes indicating a defective MSCI. Consistent with this defect, mutant sex chromosomes displayed an abnormal presence of elongating RNA polymerase II coupled with an overall increase in chromatin accessibility detectable by ATAC-seq. By investigating potential mechanisms underlying these anomalies, we identified a role for ARID1A in promoting the preferential enrichment of the histone variant, H3.3, on the sex chromosomes, a known hallmark of MSCI. Without ARID1A, the sex chromosomes appeared depleted of H3.3 at levels resembling autosomes. Higher resolution analyses by CUT&RUN revealed dramatic shifts in sex-linked H3.3 associations from discrete intergenic sites and broader gene-body domains to promoters in response to the loss of ARID1A. Several sex-linked sites displayed ectopic H3.3 occupancy that does not co-localize with DMC1 (DNA Meiotic Recombinase 1). This observation suggests a requirement for ARID1A in DMC1 localization to the asynapsed sex chromatids. We conclude that ARID1A-directed H3.3 localization influences sex chromosome gene regulation and DNA repair during meiosis I.