Prasasya Rexxi D, Mayo Kelly E
Department of Molecular Biosciences and Center for Reproductive Science, Northwestern University, Evanston, Illinois.
Endocrinology. 2018 Jan 1;159(1):184-198. doi: 10.1210/en.2017-00677.
The Notch pathway is a highly conserved juxtacrine signaling mechanism that is important for many cellular processes during development, including differentiation and proliferation. Although Notch is important during ovarian follicle formation and early development, its functions during the gonadotropin-dependent stages of follicle development are largely unexplored. We observed positive regulation of Notch activity and expression of Notch ligands and receptors following activation of the luteinizing hormone-receptor in prepubertal mouse ovary. JAG1, the most abundantly expressed Notch ligand in mouse ovary, revealed a striking shift in localization from oocytes to somatic cells following hormone stimulation. Using primary cultures of granulosa cells, we investigated the functions of Jag1 using small interfering RNA knockdown. The loss of JAG1 led to suppression of granulosa cell differentiation as marked by reduced expression of enzymes and factors involved in steroid biosynthesis, and in steroid secretion. Jag1 knockdown also resulted in enhanced cell proliferation. These phenotypes were replicated, although less robustly, following knockdown of the obligate canonical Notch transcription factor RBPJ. Intracellular signaling analysis revealed increased activation of the mitogenic phosphatidylinositol 3-kinase/protein kinase B and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways following Notch knockdown, with a mitogen-activated protein kinase kinase inhibitor blocking the enhanced proliferation observed in Jag1 knockdown granulosa cells. Activation of YB-1, a known regulator of granulosa cell differentiation genes, was suppressed by Jag1 knockdown. Overall, this study reveals a role of Notch signaling in promoting the differentiation of preovulatory granulosa cells, adding to the diverse functions of Notch in the mammalian ovary.
Notch信号通路是一种高度保守的旁分泌信号机制，对发育过程中的许多细胞进程都很重要，包括分化和增殖。尽管Notch在卵巢卵泡形成和早期发育过程中很重要，但其在卵泡发育的促性腺激素依赖阶段的功能在很大程度上尚未得到探索。我们观察到，在青春期前小鼠卵巢中，促黄体生成素受体激活后，Notch活性以及Notch配体和受体的表达受到正向调节。JAG1是小鼠卵巢中表达最丰富的Notch配体，在激素刺激后，其定位从卵母细胞显著转移到体细胞。利用颗粒细胞原代培养，我们通过小干扰RNA敲低研究了Jag1的功能。JAG1的缺失导致颗粒细胞分化受到抑制，其标志是参与类固醇生物合成的酶和因子的表达以及类固醇分泌减少。Jag1敲低还导致细胞增殖增强。在敲低必需的经典Notch转录因子RBPJ后，这些表型也会出现，尽管程度较弱。细胞内信号分析显示，Notch敲低后，促有丝分裂的磷脂酰肌醇3激酶/蛋白激酶B和丝裂原活化蛋白激酶/细胞外信号调节激酶信号通路的激活增加，一种丝裂原活化蛋白激酶激酶抑制剂可阻断Jag1敲低的颗粒细胞中观察到的增殖增强。Jag1敲低抑制了YB-1（一种已知的颗粒细胞分化基因调节因子）的激活。总体而言，这项研究揭示了Notch信号在促进排卵前颗粒细胞分化中的作用，进一步丰富了Notch在哺乳动物卵巢中的多种功能。
