Mouse sex chromosomes are enriched for co-amplified gene families, madelaine chocolate advent calendars present in tens to hundreds of copies.Co-amplification of Slx/Slxl1 on the X chromosome and Sly 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, Srsx, along with two additional partial gene annotations, is actually part of a larger transcription unit, which we name Laidx.
Laidx is harbored in a 229 kb amplicon that represents the ancestral state as compared to a 525 kb Y-amplicon containing the rearranged Laidy.Laidx contains a 25,011 nucleotide open reading frame, predominantly expressed in round spermatids, predicted to encode an 871 kD protein.Laidx has orthologous copies with the rat and also the 825-MY diverged parasitic Chinese liver fluke, Clonorchis sinensis, the likely result of a horizontal gene transfer of rodent Laidx to an ancestor of the liver fluke.
To assess the male reproductive functions of Laidx, we generated mice carrying a multi-megabase deletion of the Laidx-ampliconic region.Laidx-deficient male mice do not show detectable reproductive defects in fertility, unkinkable hose fecundity, testis histology, and offspring sex ratio.We speculate that Laidx and Laidy represent a now inactive X vs.
Y chromosome conflict that occurred in an ancestor of present day mice.