Genomic Structure, Evolutionary Origins, and Reproductive Function of a Large Amplified Intrinsically Disordered Protein-Coding Gene on the X Chromosome () in Mice.

Mouse sex chromosomes are enriched for co-amplified gene families, present in tens to hundreds of copies. Co-amplification of / on the X chromosome and on the Y chromosome are involved in dose-dependent meiotic drive, however the role of other co-amplified genes remains poorly understood. Here we demonstrate that the co-amplified gene family on the X chromosome, , along with two additional partial gene annotations, is actually part of a larger transcription unit, which we name is harbored in a 229 kb amplicon that represents the ancestral state as compared to a 525 kb Y-amplicon containing the rearranged contains a 25,011 nucleotide open reading frame, predominantly expressed in round spermatids, predicted to encode an 871 kD protein. has orthologous copies with the rat and also the 825-MY diverged parasitic Chinese liver fluke, , the likely result of a horizontal gene transfer of rodent to an ancestor of the liver fluke. To assess the male reproductive functions of , we generated mice carrying a multi-megabase deletion of the -ampliconic region. -deficient male mice do not show detectable reproductive defects in fertility, fecundity, testis histology, and offspring sex ratio. We speculate that and represent a now inactive X Y chromosome conflict that occurred in an ancestor of present day mice.