La Salle Sophie, Mertineit Carmen, Taketo Teruko, Moens Peter B, Bestor Timothy H, Trasler Jacquetta M
Department of Pharmacology and Therapeutics and the Montreal Children's Hospital Research Institute, McGill University, Montreal, QC, Canada H3H 1P3.
Dev Biol. 2004 Apr 15;268(2):403-15. doi: 10.1016/j.ydbio.2003.12.031.
The acquisition of genomic methylation in the male germ line is initiated prenatally in diploid gonocytes, while DNA methylation in the female germ line is initiated postnatally in growing oocytes. We compared the temporal expression patterns of the DNA methyltransferases, DNMT1, DNMT3a, DNMT3b, and DNMT3l in the male and female germ lines. DNMT1 expression was examined by immunocytochemistry and Northerns with an emphasis on the prenatal period. In the female, there is a gradual down-regulation of DNMT1 protein in prenatal meiotic prophase I oocytes that is not associated with the production of an untranslated transcript, as it is in the male; these results suggest that the mechanism of meiotic down-regulation differs between the sexes. In the male, DNMT1 is unlikely to play a role in the prenatal acquisition of germ line methylation patterns since it is down-regulated in gonocytes between 14.5 and 18.5 days of gestation and is absent at the time of initiation of DNA methylation. To search for candidate DNMTs that could be involved in establishing methylation patterns in both germ lines, real-time RT-PCR was used to simultaneously study the expression profiles of the three DNMT3 enzymes in developing testes and ovaries; DNMT1 expression was included as a control. Expression profiles of DNMT3a and DNMT3l provide support for an interaction of the two enzymes during prenatal germ cell development and de novo methylation in the male. DNMT3l is the predominant DNMT3 enzyme expressed at high levels in the postnatal female germ line at the time of acquisition of DNA methylation patterns. DNMT1 and DNMT3b expression levels peak concomitantly, shortly after birth in the male, consistent with a role in the maintenance of methylation patterns in proliferating spermatogonia. Together, the results provide clues to specific roles for the different DNMT family members in de novo and maintenance methylation in the developing testis and ovary.
雄性生殖系中基因组甲基化的获得在二倍体生殖母细胞中于产前开始，而雌性生殖系中的DNA甲基化在出生后生长中的卵母细胞中开始。我们比较了DNA甲基转移酶DNMT1、DNMT3a、DNMT3b和DNMT3l在雄性和雌性生殖系中的时间表达模式。通过免疫细胞化学和Northern印迹法检测DNMT1的表达，重点关注产前阶段。在雌性中，产前减数分裂前期I卵母细胞中DNMT1蛋白逐渐下调，这与雄性不同，不伴随未翻译转录本的产生；这些结果表明减数分裂下调机制在两性之间存在差异。在雄性中，DNMT1不太可能在生殖系甲基化模式的产前获得中发挥作用，因为它在妊娠14.5至18.5天之间的生殖母细胞中下调，并且在DNA甲基化开始时不存在。为了寻找可能参与建立两性生殖系甲基化模式的候选DNMT，使用实时RT-PCR同时研究发育中的睾丸和卵巢中三种DNMT3酶的表达谱；将DNMT1的表达作为对照。DNMT3a和DNMT3l的表达谱为这两种酶在产前生殖细胞发育和雄性从头甲基化过程中的相互作用提供了支持。DNMT3l是在获得DNA甲基化模式时在出生后雌性生殖系中高水平表达的主要DNMT3酶。DNMT1和DNMT3b的表达水平在雄性出生后不久同时达到峰值，这与它们在增殖精原细胞中维持甲基化模式的作用一致。总之，这些结果为不同DNMT家族成员在发育中的睾丸和卵巢的从头甲基化和维持甲基化中的特定作用提供了线索。
