The XY body is a specialized chromatin territory that forms during meiotic prophase of spermatogenesis and comprises the transcriptionally repressed sex chromosomes. Remodeling of the XY chromatin is brought about by recruitment of specific proteins to the X and Y chromosomes during meiosis, and also by post-translational modifications of histones and other chromatin-associated proteins. Here, we demonstrate that SUMO, a small ubiquitin-related modifier protein that regulates a wide variety of nuclear functions in somatic cells, dramatically localizes to the XY body. SUMO was first detected in the XY body of early pachytene spermatocytes and gradually accumulated, reaching maximal levels there during the mid to late pachytene stages. Several known SUMO substrates, including PML and DAXX, were also found to accumulate in the XY body of mid to late stage pachytene spermatocytes. These same proteins localize to PML nuclear bodies of somatic interphase nuclei. Together, these findings indicate a role for SUMO modification in regulating the structure and function of the XY body and reveal molecular similarities between the XY body and PML nuclear bodies.
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