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Curr Biol. 2019 Nov 4;29(21):3699-3706.e5. doi: 10.1016/j.cub.2019.08.057. Epub 2019 Oct 17.

A Neofunctionalized X-Linked Ampliconic Gene Family Is Essential for Male Fertility and Equal Sex Ratio in Mice.

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Department of Human Genetics, University of Michigan Medical School, 1241 E. Catherine Street, Ann Arbor, MI 48109, USA.
Reproductive Biology Group, Division of Developmental Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands; Center for Reproductive Medicine, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands.
Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, 333 Burnet Avenue, Cincinnati, OH 45229, USA; Department of Pediatrics, University of Cincinnati College of Medicine, 333 Burnet Avenue, Cincinnati, OH 45229, USA.
Department of Human Genetics, University of Michigan Medical School, 1241 E. Catherine Street, Ann Arbor, MI 48109, USA. Electronic address:


The mammalian sex chromosomes harbor an abundance of newly acquired ampliconic genes, although their functions require elucidation [1-9]. Here, we demonstrate that the X-linked Slx and Slxl1 ampliconic gene families represent mouse-specific neofunctionalized copies of a meiotic synaptonemal complex protein, Sycp3. In contrast to the meiotic role of Sycp3, CRISPR-loxP-mediated multi-megabase deletions of the Slx (5 Mb) and Slxl1 (2.3Mb) ampliconic regions result in post-meiotic defects, abnormal sperm, and male infertility. Males carrying Slxl1 deletions sire more male offspring, whereas males carrying Slx and Slxl1 duplications sire more female offspring, which directly correlates with Slxl1 gene dosage and gene expression levels. SLX and SLXL1 proteins interact with spindlin protein family members (SPIN1 and SSTY1/2) and males carrying Slxl1 deletions downregulate a sex chromatin modifier, Scml2, leading us to speculate that Slx and Slxl1 function in chromatin regulation. Our study demonstrates how newly acquired X-linked genes can rapidly evolve new and essential functions and how gene amplification can increase sex chromosome transmission.


X chromosome; gene dosage; male infertility; meiotic drive


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