Battle of the Sex Chromosomes: Competition between X and Y Chromosome-Encoded Proteins for Partner Interaction and Chromatin Occupancy Drives Multicopy Gene Expression and Evolution in Muroid Rodents

Mol Biol Evol. 2020 Dec 16;37(12):3453-3468. doi: 10.1093/molbev/msaa175.


Transmission distorters (TDs) are genetic elements that favor their own transmission to the detriments of others. Slx/Slxl1 (Sycp3-like-X-linked and Slx-like1) and Sly (Sycp3-like-Y-linked) are TDs, which have been coamplified on the X and Y chromosomes of Mus species. They are involved in an intragenomic conflict in which each favors its own transmission, resulting in sex ratio distortion of the progeny when Slx/Slxl1 versus Sly copy number is unbalanced. They are specifically expressed in male postmeiotic gametes (spermatids) and have opposite effects on gene expression: Sly knockdown leads to the upregulation of hundreds of spermatid-expressed genes, whereas Slx/Slxl1-deficiency downregulates them. When both Slx/Slxl1 and Sly are knocked down, sex ratio distortion and gene deregulation are corrected. Slx/Slxl1 and Sly are, therefore, in competition but the molecular mechanism remains unknown. By comparing their chromatin-binding profiles and protein partners, we show that SLX/SLXL1 and SLY proteins compete for interaction with H3K4me3-reader SSTY1 (Spermiogenesis-specific-transcript-on-the-Y1) at the promoter of thousands of genes to drive their expression, and that the opposite effect they have on gene expression is mediated by different abilities to recruit SMRT/N-Cor transcriptional complex. Their target genes are predominantly spermatid-specific multicopy genes encoded by the sex chromosomes and the autosomal Speer/Takusan. Many of them have coamplified with not only Slx/Slxl1/Sly but also Ssty during muroid rodent evolution. Overall, we identify Ssty as a key element of the X versus Y intragenomic conflict, which may have influenced gene content and hybrid sterility beyond Mus lineage since Ssty amplification on the Y predated that of Slx/Slxl1/Sly.

Keywords: H3K4 methylation; gene regulation; intragenomic conflict; multicopy genes; rodent; sex chromosomes; sex ratio; spermatogenesis; transmission distorters.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Evolution*
  • Cell Cycle Proteins / genetics
  • DNA-Binding Proteins / genetics
  • Male
  • Mice, Inbred C57BL
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism
  • Protein Kinases / genetics
  • Proteins / genetics*
  • Proteins / metabolism
  • Spermatids / metabolism
  • Transcription Initiation Site
  • X Chromosome / genetics*
  • Y Chromosome / genetics*


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Nuclear Proteins
  • Proteins
  • Slx protein, mouse
  • Slx-like1 protein, mouse
  • Ssty1 protein, mouse
  • Sycp3 protein, mouse
  • Protein Kinases
  • Smok1 protein, mouse