Loss of YY1 Impacts the Heterochromatic State and Meiotic Double-Strand Breaks during Mouse Spermatogenesis

Abstract

The progression of spermatogenesis involves global changes in chromatin structure and conformation. However, our understanding of the regulation of chromatin changes in germ cells remains limited. Here we describe both in vivo RNA interference and genetic mouse knockout studies that identify a critical role for Yin Yang 1 (YY1) in mammalian spermatogenesis. In the YY1-deficient spermatocytes, we find a significant decrease in the global level of the heterochromatin markers (H3K9me3 and HP1-gamma) and a concomitant increase in the double-strand break (DSB) signals on chromosomes (gamma-H2AX, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling, and Rad51) at the leptotene/zygotene stages of spermatocytes. These findings support a link between chromatin modifications and meiotic DSB formation, as has been seen in other model organisms. We propose that a depletion of YY1 may alter the structural integrity of heterochromatin, rendering it more accessible to the DSB machinery. In addition, YY1-deficient spermatocytes show univalent formation, increased aneuploidy, and pachytene cell death, which are likely due to defects in DNA repair. Taken together, this study identifies an important role for YY1 in mouse meiosis and provides new insight into mechanisms that regulate mammalian spermatogenesis.

ACKNOWLEDGMENTS

We are indebted to Xuecai Ge and Li-Huei Tsai for technical assistance with the in vivo RNAi experiments. We thank Klaus Rajewsky for critical reading of the manuscript and for providing the CD21-Cre3A mice and George C. Enders for the GCNA antibody. We thank the DF/HCC Research Pathology Core and Rodent Histopathology Core for assistance with histology, particularly Roderick Bronson and Jeff Kutok. We thank the Arlene Sharpe laboratory and the optical imaging program of the Harvard NeuroDiscovery Center, particularly Lai Ding, for assistance with microscopy. We thank Monica Colaiacovo for critical reading of the manuscript, the former and current members of the Shi laboratory for unfailing support and encouragement, and the Page laboratory members for scientific discussions.

This work was supported by a grant from the NIH to Y.S. (no. GM053874).