Kruger, A. N. | bioRxiv Science

bioRxiv2024

Reenacting a mouse genetic evolutionary arms race in yeast reveals SLXL1/SLX compete with SLY1/2 for binding to Spindlins.

The house mouse X and Y chromosomes have recently acquired high copy number, rapidly evolving gene families representing an evolutionary arms race. This arms race between proteins encoded by X-linked Slxl1/Slx and Y-linked Sly gene families can distort male offspring sex ratio, but how these proteins compete remains unknown. Here, we report how Slxl1/Slx and Sly encoded proteins compete in a protein family-specific and dose-dependent manner using yeast. Specifically, SLXL1 competes with SLY1 and SLY2 for binding to the Spindlin SPIN1. Similarly, SLX competes with SLY2 for binding the Spindlin SSTY2. These competitions are driven by the N-termini of SLXL1, SLX, SLY1, and SLY2 binding to the third Tudor domains of SPIN1 and SSTY2. SLY1 and SLY2 form homo- and heterodimers, suggesting the competition is between complex multimers. Residues under positive selection mapping to the interaction domains and rapid exon gain/loss are consistent with competition between the X- and Y-linked gene families. Our findings support a model in which dose-dependent competition of these X- and Y-linked encoded proteins to bind Spindlins occurs in haploid X- and Y-spermatids to influence X-versus Y-sperm fitness and thus sex ratio. Significance StatementIn house mouse, an evolutionary arms race between proteins encoded by the X-linked Slxl1/Slx and Y-linked Sly gene families during spermatogenesis can distort male offspring sex ratio, but how these proteins compete remains unknown. We report how SLXL1/SLX competes with SLY1/SLY2 by demonstrating their dose-dependent competitive binding to Spindlins, the key protein domains and rapidly evolving residues and exons that drive the competition, and how the competition is likely between complex multimers. Our findings have broad implications for the mechanics of evolutionary arms and how competition between sex chromosomes influences X-versus Y-sperm fitness and sex ratio.

genetics↗

bioRxiv2018

Male mice with large inversions or deletions of X-palindrome arms are fertile and express their associated genes post-meiosis.

Large (>10 kb) palindromic sequences are enriched on mammalian sex chromosomes. In mice, these palindromes harbor gene families ([≥]2 gene copies) expressed exclusively in post-meiotic testicular germ cells, at a time when most single-copy sex-linked genes are transcriptionally repressed. This distinct expression pattern led to the hypothesis that containment within palindrome structures or having [≥]2 gene enables post-meiotic gene expression. We tested these two hypotheses by using CRISPR to precisely engineer large (10s of kb) inversions and deletions of X chromosome palindrome arms for two regions carrying the mouse 4930567H17Rik and Mageb5 gene families. We found that 4930567H17Rik and Mageb5 gene expression is unaffected in mice carrying palindrome arm inversions, suggesting that palindromic structure is not important for mediating palindrome-associated gene expression. We also found that 4930567H17Rik and Mageb5 gene expression is reduced by half in mice carrying palindrome arm deletions, allowing us to test whether palindrome-associated genes are sensitive to reduced expression levels resulting in spermatogenic defects. Male mice carrying palindrome arm deletions of 4930567H17Rik or Mageb5, however, are fertile, have normal testis histology, and show no aberrations in spermatogenic cell population frequencies via FACS quantification. Together, these findings suggest that large palindromic structures on the sex chromosomes are not necessary for their associated genes to evade post-meiotic transcriptional repression and that these genes are not sensitive to reduced expression levels. Large sex chromosome palindromes may thus be important for other reasons, such as the long-term evolutionary stability of their associated gene families.

genetics↗