Extensive survey of meiotic metaphase II arrest during oocyte maturation in vertebrates revealed that the mitogen-activated protein kinase (MAPK) pathway regulated by the c-mos proto-oncogene product, Mos, has an essential role in cytostatic activity, termed cytostatic factor (CSF). In contrast, little is known in invertebrates in which meiotic arrest occurs in most cases at metaphase I (MI arrest). A parthenogenetic insect, the sawfly Athalia rosae, in which artificial egg activation is practicable, has advantages to investigate the mechanisms of MI arrest. Both the MAPK/extracellular signal-regulated protein kinase kinase (MEK) and MAPK were phosphorylated and maintained active in MI-arrested sawfly eggs, whereas they were dephosphorylated soon after egg activation. Treatment of MI-arrested eggs with U0126, an inhibitor of MEK, resulted in dephosphorylation of MAPK and MI arrest was resumed. The sawfly c-mos gene orthologue encoding a serine/threonine kinase was cloned and analyzed. It was expressed in nurse cells in the ovaries. To examine CSF activity of the sawfly Mos, synthesized glutathione S-transferase (GST)-fusion sawfly Mos protein was injected into MI-resumed eggs in which MEK and MAPK were dephosphorylated. Both MEK and MAPK were phosphorylated again upon injection. In these GST-fusion sawfly Mos-injected eggs subsequent mitotic (syncytial) divisions were blocked and embryonic development was ceased. These results demonstrated that the MEK-MAPK pathway was involved in maintaining CSF arrest in sawfly eggs and Mos functioned as its upstream regulatory molecule.

译文

对脊椎动物卵母细胞成熟过程中减数分裂中期II停滞的广泛调查表明,由c-mos原癌基因产物Mos调节的丝裂原活化蛋白激酶 (MAPK) 途径在细胞抑制活性中具有重要作用,称为细胞抑制因子 (CSF)。相反,在无脊椎动物中鲜为人知,在大多数情况下,减数分裂停滞发生在中期I (MI停滞)。一种孤雌生殖昆虫,锯蝇Athalia rosae,在人工卵激活中是可行的,具有研究MI阻滞机制的优势。MAPK/细胞外信号调节蛋白激酶 (MEK) 和MAPK在MI被捕的锯蝇卵中均被磷酸化并保持活性,而在卵激活后不久就被去磷酸化。用MEK抑制剂U0126处理MI停滞的卵,导致MAPK去磷酸化,并恢复MI停滞。克隆并分析了编码丝氨酸/苏氨酸激酶的sawfly c-mos基因直系同源物。它在卵巢的护士细胞中表达。为了检查锯蝇Mos的CSF活性,将合成的谷胱甘肽S-转移酶 (GST) 融合的锯蝇Mos蛋白注射到MI恢复的卵中,其中MEK和MAPK被去磷酸化。注射后,MEK和MAPK均再次磷酸化。在这些GST融合的sawfly Mos注入的卵中,随后的有丝分裂 (合胞体) 分裂被阻断,并且停止了胚胎发育。这些结果表明,mek-mapk途径参与维持锯蝇卵中CSF的停滞,而Mos充当其上游调节分子。

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