Kashima Koji, Kano Kiyoshi, Naito Kunihiko
Laboratory of Applied Genetics, Graduate School of Agriculture and Life Science, University of Tokyo, Japan.
J Reprod Dev. 2007 Dec;53(6):1175-82. doi: 10.1262/jrd.19075. Epub 2007 Sep 4.
Mos and the mitogen-activated protein kinase (MAPK) cascade have been established as crucial regulators of second meiotic metaphase arrest, the so-called CSF arrest, in mammalian oocytes. They are also thought to play a role in regulating mitotic metaphase arrest of early mammalian embryos. In the present study, we examined whether mitotic arrest is induced in early mouse embryos by activation of extracellular signal-regulated kinases (ERKs), which are major MAPKs in mouse eggs, and their substrate, p90Ribosomal S6 kinase (RSK), as reported in Xenopus embryos. Wild-type Mos (wt-Mos), degradation-resistant Mos mutant (P2G-Mos) or constitutive active mutant of MAPK/ERK kinase, MEK (SDSE-MEK), was expressed in early mouse embryos by injecting the respective expression vectors into the pronucleus of fertilized eggs, and the developmental rates were then examined up to 72 h after insemination. Expression of P2G-Mos and SDSE-MEK succeeded in activating ERKs and RSK in developing mouse embryos, while wt-Mos failed to activate them in spite of expression of mos mRNA, indicating that the wt-Mos protein is unstable in early mouse embryos. Although the activated levels of ERKs and RSK in the vector-injected embryos were comparable to those of meiotically arrested mouse oocytes, their developmental rates were identical to those of the control embryos. These results suggest that activation of MAPK and RSK does not induce mitotic arrest in early mouse embryos. The present study indicates that there are large physiological differences between early mouse embryos and mouse oocytes and that CSF arrest of mouse eggs in mitosis should be discussed separately from that in meiosis.
Mos和丝裂原活化蛋白激酶（MAPK）级联已被确认为哺乳动物卵母细胞第二次减数分裂中期阻滞（即所谓的CSF阻滞）的关键调节因子。它们也被认为在调节早期哺乳动物胚胎的有丝分裂中期阻滞中发挥作用。在本研究中，我们研究了如非洲爪蟾胚胎中所报道的，通过激活细胞外信号调节激酶（ERKs，小鼠卵中的主要MAPK）及其底物p90核糖体S6激酶（RSK），是否能在早期小鼠胚胎中诱导有丝分裂阻滞。通过将各自的表达载体注射到受精卵的原核中，在早期小鼠胚胎中表达野生型Mos（wt-Mos）、抗降解Mos突变体（P2G-Mos）或MAPK/ERK激酶MEK的组成型活性突变体（SDSE-MEK），然后检查受精后72小时内的发育率。P2G-Mos和SDSE-MEK的表达成功激活了发育中的小鼠胚胎中的ERKs和RSK，而wt-Mos尽管有mos mRNA的表达却未能激活它们，这表明wt-Mos蛋白在早期小鼠胚胎中不稳定。尽管注射载体的胚胎中ERKs和RSK的激活水平与减数分裂阻滞的小鼠卵母细胞相当，但其发育率与对照胚胎相同。这些结果表明，MAPK和RSK的激活不会在早期小鼠胚胎中诱导有丝分裂阻滞。本研究表明，早期小鼠胚胎和小鼠卵母细胞之间存在很大的生理差异，并且小鼠卵在有丝分裂中的CSF阻滞应与减数分裂中的CSF阻滞分开讨论。
