The male pachynema-specific protein MAPS drives phase separation in vitro and regulates sex body formation in vivo

Highly dynamic chromosome remodeling and extensive nuclear compartmentalization occur during mammalian meiotic prophase I. We report here that mouse spermatocytes lacking MAPS, the male pachynema-specific protein, exhibit multiple pachytene defects, including disordered chromatin accessibility, interrupted nucleosome composition, and globally altered transcription, accompanied by disturbed nucleus phase formation. Adult Maps-/- pachytene spermatocytes lack sex body formation and exhibit improper autosomal chromatin condensation, which can be attributed to the feature of MAPS to mediate phase separation through its unique intrinsically disordered regions (IDRs), amino acids 2-9. MAPS protein with deletion of IDR failed to form a distinguishable phase in vitro and in cultured cells, and remarkably, MAPS IDR-deleted male mice suffer from pachytene arrest and sterility, with a typical absence of sex body and less condensed autosomal chromosomes, similar to Maps-/- mice. Thus, the nucleus phase separation mediated by MAPS may be essential for male pachynema progression in mice. Overall design: To check the MSCI status of pachytene cells after MAPS protein deletion, pachytene cells from WT, MAPS-/- and MAPSEE;MAPS-/- groups (postnatal date ~80 day) were purified by STA-PUT method. Three mice with identical genotypes for each group were used for pachytene cell purification. RNA-seq were conducted with two independent experiments.

哺乳动物减数分裂前期I期间，会发生高度动态的染色质重塑与广泛的细胞核区室化过程。本研究显示，缺失雄性粗线期特异性蛋白MAPS（male pachynema-specific protein）的小鼠精母细胞存在多种粗线期缺陷：包括染色质可及性紊乱、核小体组成紊乱、全基因组转录谱改变，同时伴随细胞核相形成障碍。成年Maps-/-小鼠的粗线期精母细胞无法形成性体，且常染色体染色质凝缩异常，这一表型可归因于MAPS通过其位于氨基酸2-9位的独特固有无序区域（intrinsically disordered regions, IDRs）介导相分离的功能。缺失IDR的MAPS蛋白无法在体外及培养细胞中形成可辨识的相结构；值得注意的是，IDR敲除的雄性小鼠同样会出现粗线期阻滞与不育，表现为典型的性体缺失及常染色体染色质凝缩不足，与Maps-/-小鼠表型一致。综上，MAPS介导的细胞核相分离可能对小鼠雄性粗线期进程至关重要。实验设计：为验证MAPS蛋白缺失后粗线期细胞的减数分裂性染色体沉默（meiotic sex chromosome inactivation, MSCI）状态，本研究通过STA-PUT细胞分离法，从野生型（wild type, WT）、MAPS-/-及MAPSEE;MAPS-/-组（出生后约80日龄）小鼠中纯化粗线期精母细胞。每组选取3只基因型一致的小鼠用于细胞纯化，随后通过两次独立实验完成RNA测序（RNA-seq）。