Abstract
During spermatogenesis, nuclear architecture of male germ cells is dynamically changed and epigenetic modifications, in particular methylation of histones, highly contribute to its regulation as well as differentiation of male germ cells. Although several methyltransferases and demethylases for histone H3 are involved in the regulation of spermatogenesis, roles of either histone H4 lysine 20 (H4K20) methyltransferases or H4K20 demethylases during spermatogenesis still remain to be elucidated. Recently, RSBN1 which is a testis-specific gene expressed in round spermatids was identified as a demethylase for dimethyl H4K20. In this study, therefore, we confirm the demethylase function of RSBN1 and compare distributions between RSBN1 and methylated H4K20 in the seminiferous tubules. Unlike previous report, expression analyses for RSBN1 reveal that RSBN1 is not a testis-specific gene and is expressed not only in round spermatids but also in elongated spermatids. In addition, RSBN1 can demethylate not only dimethyl H4K20 but also trimethyl H4K20 and could convert both dimethyl H4K20 and trimethyl H4K20 into monomethyl H4K20. When distribution pattern of RSBN1 in the seminiferous tubule is compared to that of methylated H4K20, both dimethyl H4K20 and trimethyl H4K20 but not monomethyl H4K20 are disappeared from RSBN1 positive germ cells, suggesting that testis-specific distribution patterns of methylated H4K20 might be constructed by RSBN1. Thus, novel expression and function of RSBN1 could be useful to comprehend epigenetic regulation during spermatogenesis.
Highlights
Spermatogenesis is the process to form spermatozoa in the seminiferous tubules of the testis
The strong H4K20me1 signal was detected in post-meiotic germ cells at the stages III through XII but not in round spermatids at the stage I, whereas the H4K20me1 signal was detected in spermatogonia and zygotene spermatocytes but not in pachytene spermatocytes (Fig 1A)
H4K20me2 was strong in pre-leptotene and zygotene spermatocytes, moderate in pachytene spermatocytes, and weak in round spermatids at the stages I to V (Fig 1B)
Summary
Spermatogenesis is the process to form spermatozoa in the seminiferous tubules of the testis. Starting with the proliferation stage, mitotic divisions cause spermatogonia, which located on the basement membrane of the tubules, to differentiate into spermatocytes. Distributions of RSBN1 and methylated H4K20 during spermatogenesis (26114506 to TI) from the Ministry of Education, Culture, Sports, Sciences, and Technology of Japan, Research Fellowships of Japan Society for the Promotion of Science for Young Scientists (to TI), Takeda Science Foundation (to NI), and Inamori Foundation (to TI).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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