Persistent Requirement and Alteration of the Key Targets of PRDM1 during Primordial Germ Cell Development in Mice

Primordial germ cells (PGCs) are the foundation of totipotency and vital for reproduction and heredity. PGCs in mice arise from the epiblast around Embryonic Day (E) 7.0, migrate through the hindgut endoderm, and colonize and proliferate in the embryonic gonads until around E13.5 prior to their differentiation either into pro-spermatogonia or oogonia. PRDM1, a transcriptional repressor, plays an essential role in PGC specification that includes robustly repressing a somatic mesodermal program. Using an inducible conditional knockout system, we show here that PRDM1 is critically required throughout PGC development. When Prdm1 was deleted in migrating PGCs at E9.5/E10.5 or in male gonadal PGCs at E11.5, PGCs were eliminated by apoptosis from around E10/5/E11.5 or E13.5, respectively. When Prdm1 was deleted in female gonadal PGCs at E11.5, PGCs progressed into the first meiotic prophase in an apparently normal fashion, but the oogonia exhibited an aberrant pachytene phenotype, undergoing abrupt apoptosis from around E16.5. The escape of a fraction of PGCs (~10%) from the Prdm1 deletion was sufficient to recover fairly normal germ-cell pools both in male and female adults. The key targets of PRDM1 in migrating/gonadal PGCs, including genes for development, apoptosis, and pro-spermatogonial differentiation, showed only a modest overlap with those upon PGC specification and were enriched with histone H3 lysine 27 tri-methylation (H3K27me3). Our findings provide a critical insight into the mechanism for maintaining the transcriptional integrity of PGCs. Overall design: Examination of Prdm1 conditional knock-out primordial germ cells

原始生殖细胞（Primordial germ cells，PGCs）是细胞全能性的核心基础，对生殖与遗传过程至关重要。小鼠体内的PGCs约于胚胎第7.0天（Embryonic Day，E7.0）从上胚层起源，经后肠内胚层迁移，并在胚胎性腺中定植与增殖，直至约E13.5天，随后分化为精原祖细胞或卵原细胞。PRDM1作为一种转录抑制因子（transcriptional repressor），在PGC特化过程中发挥不可或缺的作用，可强力抑制体细胞中胚层程序。本研究通过诱导型条件性敲除系统证实，PRDM1在PGC发育全程均发挥关键调控功能。当于E9.5/E10.5时期在迁移中的PGCs内敲除Prdm1，或于E11.5时期在雄性性腺PGCs内敲除Prdm1时，PGCs分别于约E10.5/E11.5及E13.5天左右通过细胞凋亡被清除。当于E11.5时期在雌性性腺PGCs内敲除Prdm1时，PGCs可正常推进至减数分裂前期Ⅰ，但卵原细胞会出现异常粗线期表型，并于约E16.5天左右突发细胞凋亡。约10%的PGCs可逃脱Prdm1敲除，这一比例足以使雌雄成年个体恢复至近乎正常的生殖细胞库水平。迁移中/性腺PGCs内PRDM1的关键靶基因（涵盖发育、凋亡及精原祖细胞分化相关基因）与PGC特化时期的靶基因仅存在少量重叠，且富集组蛋白H3赖氨酸27三甲基化（H3K27me3）标记。本研究结果为维持PGCs转录完整性的分子机制提供了关键见解。整体实验设计：对Prdm1条件性敲除的原始生殖细胞进行检测。