Bisection of the X Chromosome Disrupts the Initiation of Chromosome Silencing during Meiosis in Caenorhabditis elegans

During meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments were enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome were upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed. CRISPR mediated bisection of the X chromosoeme in C. elegans to create YBT7 strain. Comparative transcriptomics of YBT74 to WT