Department of Pathology, Medical School, Osaka University, Osaka, Japan.
Japan Agency for Medical Research and Development (AMED)-CREST, Tokyo, Japan.
Biol Reprod. 2019 Jul 1;101(1):248-256. doi: 10.1093/biolre/ioz056.
PIWI-interacting RNAs (piRNAs), a subclass of germ cell-specific noncoding small RNAs, are essential for de novo DNA methylation of retrotransposon genes in embryonic testes. PIWIL2/MILI, one of three mouse PIWI family members, is indispensable for piRNA production, DNA methylation of retrotransposons presumably via piRNA, and normal spermatogenesis. In vitro analysis using germline stem cells (GS cells) revealed that glycerol-3-phosphate acyltransferase 2 (GPAT2), which is a mitochondrial outer membrane protein involved in generation of lysophosphatidic acid (LPA) and highly expressed in testes, plays important roles in spermatogenesis. Namely, GPAT2 binds to PIWIL2 and is closely involved in the biogenesis of piRNAs; this process is independent of its enzymatic activity on LPA. However, GS cells recapitulate only a limited phase of spermatogenesis and the biological functions of GPAT2 remain largely unknown. In this study, we generated GPAT2-deficient mice and conducted comprehensive analyses. The deficient mice showed defective piRNA production and subsequent de-silencing of IAP and Line-1 retrotransposons in fetal testes. In addition, apoptosis of pachytene spermatocytes was observed. These abnormalities were all common to the phenotype of PIWIL2-deficient mice, in which piRNA production was impaired. GPAT2-deficient mice exhibited apoptosis in spermatogonia at the neonatal stage, which was not observed in PIWIL2-deficient mice. These data show that GPAT2 plays a critical role in preventing apoptosis in spermatogonia.
PIWI 相互作用 RNA（piRNA）是一类生殖细胞特异性非编码小 RNA，对于胚胎睾丸中逆转录转座子基因的从头 DNA 甲基化至关重要。PIWIL2/MILI 是三种小鼠 PIWI 家族成员之一，对于 piRNA 的产生、逆转录转座子的 DNA 甲基化以及正常精子发生是必不可少的。使用生殖细胞干细胞（GS 细胞）进行的体外分析表明，甘油-3-磷酸酰基转移酶 2（GPAT2）是一种参与产生溶血磷脂酸（LPA）的线粒体外膜蛋白，在睾丸中高度表达，在精子发生中发挥重要作用。即，GPAT2 与 PIWIL2 结合，并密切参与 piRNA 的生物发生；这个过程不依赖于其对 LPA 的酶活性。然而，GS 细胞仅能再现精子发生的有限阶段，并且 GPAT2 的生物学功能在很大程度上仍然未知。在这项研究中，我们生成了 GPAT2 缺陷型小鼠并进行了全面分析。缺陷型小鼠显示出胎儿睾丸中 piRNA 产生的缺陷以及随后 IAP 和 LINE-1 逆转录转座子的去沉默。此外，还观察到粗线期精母细胞的凋亡。这些异常与 PIWIL2 缺陷型小鼠的表型均相同，其中 piRNA 的产生受损。GPAT2 缺陷型小鼠在新生阶段的精原细胞中表现出凋亡，而在 PIWIL2 缺陷型小鼠中则未观察到。这些数据表明，GPAT2 在防止精原细胞凋亡中发挥关键作用。
