Kawashima Ikko, Umehara Takashi, Noma Noritaka, Kawai Tomoko, Shitanaka Manami, Richards Joanne S, Shimada Masayuki
Laboratory of Reproductive Endocrinology (I.K., T.U., N.N., T.K., M.S., M.S.), Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima,739-8528, Japan; and Department of Molecular and Cellular Biology (J.S.R.), Baylor College of Medicine, Houston, Texas 77030.
Mol Endocrinol. 2014 May;28(5):706-21. doi: 10.1210/me.2013-1316. Epub 2014 Mar 20.
Neuregulin 1 (NRG1) is induced in granulosa cells by LH and acts on granulosa and cumulus cells during ovulation. In this study, we sought to determine the role of NRG1 in oocyte maturation by generating a granulosa cell-specific Nrg1 knockout mouse (Nrg1(flox/flox);Cyp19a1Cre mice [gcNrg1KO]). In the gcNrg1KO mice, meiosis was induced 2 hours earlier than in control mice. More than 60% of the oocytes in the mutant mice spontaneously re-resumed meiosis beyond the MII stage. The percentage of successful fertilization was comparable in oocytes of both genotypes collected at 14 or 16 hours after human chorionic gonadotropin injection but was significantly lower in oocytes of the gcNrg1KO mice at 18 or 20 hours. The number of pups per litter was significantly decreased in gcNrg1KO mice. To determine the molecular events associated with the abnormal progression of meiosis in the gcNrg1KO mouse oocytes, the defects of cumulus/granulosa cell functions were analyzed. The expression of genes involved in luteinization and cumulus expansion was significantly higher at 2 hours after human chorionic gonadotropin injection in the gcNrg1KO mice; this was related to abnormal activation of protein kinase C (PKC) and phosphorylation of connexin-43 in cumulus cells. Changes in connexin-43 by PKC might lead to early meiotic resumption of oocytes in gcNrg1KO mice. We conclude that NRG1 is induced by LH in mural granulosa cells and exerts an important regulatory role in oocyte meiotic maturation and competence by reducing PKC activation in cumulus cells and preventing premature progression to the MII stage that leads to abnormal fertilization and fertility.
神经调节蛋白1（NRG1）由促黄体生成素（LH）诱导产生于颗粒细胞中，并在排卵过程中作用于颗粒细胞和卵丘细胞。在本研究中，我们通过构建颗粒细胞特异性Nrg1基因敲除小鼠（Nrg1(flox/flox);Cyp19a1Cre小鼠 [gcNrg1KO]）来确定NRG1在卵母细胞成熟中的作用。在gcNrg1KO小鼠中，减数分裂比对照小鼠提前2小时开始诱导。超过60%的突变小鼠卵母细胞在MII期后自发重新恢复减数分裂。在人绒毛膜促性腺激素注射后14或16小时收集的两种基因型的卵母细胞中，成功受精的百分比相当，但在18或20小时时，gcNrg1KO小鼠的卵母细胞受精率显著降低。gcNrg1KO小鼠每窝幼崽的数量显著减少。为了确定与gcNrg1KO小鼠卵母细胞减数分裂异常进程相关的分子事件，我们分析了卵丘/颗粒细胞功能的缺陷。在gcNrg1KO小鼠中，人绒毛膜促性腺激素注射后2小时，参与黄体化和卵丘扩展的基因表达显著升高；这与卵丘细胞中蛋白激酶C（PKC）的异常激活和连接蛋白43的磷酸化有关。PKC引起的连接蛋白43变化可能导致gcNrg1KO小鼠卵母细胞减数分裂过早恢复。我们得出结论，NRG1由壁层颗粒细胞中的LH诱导产生，并通过降低卵丘细胞中PKC的激活以及防止过早进入MII期（这会导致异常受精和生育力），在卵母细胞减数分裂成熟和能力方面发挥重要的调节作用。
