XY Body Of Spermatocytes Research Articles

Novel localizations and interactions of intercellular bridge proteins revealed by proteomic profiling†.

Intercellular bridges (ICBs) connecting germ cells are essential for spermatogenesis, and their deletion causes male infertility. However, the functions and component factors of ICBs are still unknown. We previously identified novel ICB-associated proteins by proteomics analysis using ICB enrichment. Here, we performed immunoprecipitation-proteomics analyses using antibodies specific to known ICB proteins MKLP1, RBM44, and ectoplasmic specialization-associated protein KIAA1210 and predicted protein complexes in the ICB cores. KIAA1210, its binding protein topoisomerase2B (TOP2B), and tight junction protein ZO1 were identified as novel ICB proteins. On the other hand, as well as KIAA1210 and TOP2B, MKLP1 and RBM44, but not TEX14, were localized at the XY body of spermatocytes, suggesting that there is a relationship between ICB proteins and meiotic chromosomes. Moreover, small RNAs interacted with an ICB protein complex that included KIAA1210, RBM44, and MKLP1. These results indicate dynamic movements of ICB proteins and suggest that ICB proteins could be involved not only in the communication between germ cells but also in their epigenetic regulation. Our results provide a novel perspective on the function of ICBs and could be helpful in revealing the biological function of the ICB.

Polycomb Protein SCML2 Associates with USP7 and Counteracts Histone H2A Ubiquitination in the XY Chromatin during Male Meiosis

Polycomb group proteins mediate transcriptional silencing in diverse developmental processes. Sex chromosomes undergo chromosome-wide transcription silencing during male meiosis. Here we report that mouse SCML2 (Sex comb on midleg-like 2), an X chromosome-encoded polycomb protein, is specifically expressed in germ cells, including spermatogonia, spermatocytes, and round spermatids. SCML2 associates with phosphorylated H2AX and localizes to the XY body in spermatocytes. Loss of SCML2 in mice causes defective spermatogenesis, resulting in sharply reduced sperm production. SCML2 interacts with and recruits a deubiquitinase, USP7, to the XY body in spermatocytes. In the absence of SCML2, USP7 fails to accumulate on the XY body, whereas H2A monoubiquitination is dramatically augmented in the XY chromatin. Our results demonstrate that the SCML2/USP7 complex constitutes a novel molecular pathway in modulating the epigenetic state of sex chromosomes during male meiosis.

Restricted Expression of Ovol2/MOVO in XY Body of Mouse Spermatocytes at the Pachytene Stage

The development of multicellular organisms is controlled by sequential activation of a hierarchy of regulatory genes, which encode transcription factors having DNA-binding motifs. We previously identified a testis-specific zinc finger transcriptional factor, Ovol2/MOVO, as a mouse homologue of Drosophila Ovo. Because mice deficient in Ovol2/Movo die during early embryogenesis, its function in male germ cells has remained unknown. We have recently succeeded in preparing anti-Ovol2/MOVO antiserum for immunohistochemical use. In the present study, we demonstrated that Ovol2/MOVO protein started to be expressed in male germ cells at 2 weeks after birth and that Ovol2/MOVO expression was restricted to the XY body in spermatocytes at the pachytene stage. In a reporter assay, Ovol2/MOVO repressed the histone H1t promoter activity in the spermatogenic cell line GC-2spd. These results suggest that Ovol2/MOVO may play an important role in the XY body during spermatogenesis, possibly in the processes of XY body formation and meiotic sex chromosome inactivation.