Expression evolution of ancestral XY gametologs across all major groups of placental mammals

Abstract

Placentalmammals present 180 million-year-old Y chromosomes that have retained a handful of dosage-sensitive genes. However, the expression evolution ofY-linked genes across placental groups has remained largely unexplored.Here,we expanded thenumber of Y gametolog sequences by analyzing ten additional species from previously unexplored groups.We detected seven remarkably conserved genes across 25 placental specieswith known Y repertoires.We then used RNA-seq data from17 placentalmammals to unveil the expression evolution of XY gametologs.We found that Y gametologs followed, on average, a 3-fold expression loss and that X gametologs also experienced some expression reduction, particularly in primates. Y gametologs gained testis specificity through an accelerated expression decay in somatic tissues. Moreover, despite the substantial expression decay of Y genes, the combined expression of XY gametologs in males is higher than that of both X gametologs in females. Finally, our work describes several features of the Y chromosome in the last common mammalian ancestor.