Current Biology
Volume 16, Issue 7, 4 April 2006, Pages 660-667
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Postmeiotic Sex Chromatin in the Male Germline of Mice

https://doi.org/10.1016/j.cub.2006.01.066Get rights and content
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Summary

In mammals, the X and Y chromosomes are subject to meiotic sex chromosome inactivation (MSCI) during prophase I in the male germline, but their status thereafter is currently unclear. An abundance of X-linked spermatogenesis genes has spawned the view that the X must be active 1, 2, 3, 4, 5, 6, 7, 8. On the other hand, the idea that the imprinted paternal X of the early embryo may be preinactivated by MSCI suggests that silencing may persist longer 9, 10, 11, 12. To clarify this issue, we establish a comprehensive X-expression profile during mouse spermatogenesis. Here, we discover that the X and Y occupy a novel compartment in the postmeiotic spermatid and adopt a non-Rabl configuration. We demonstrate that this postmeiotic sex chromatin (PMSC) persists throughout spermiogenesis into mature sperm and exhibits epigenetic similarity to the XY body. In the spermatid, 87% of X-linked genes remain suppressed postmeiotically, while autosomes are largely active. We conclude that chromosome-wide X silencing continues from meiosis to the end of spermiogenesis, and we discuss implications for proposed mechanisms of imprinted X-inactivation.

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Present address: Department of Biopharmaceutical Sciences, University of California at San Francisco, San Francisco, California 94243.