Department of Entomology, University of Georgia, Athens, GA, 30602, USA.
Department of Entomology, University of Georgia, Athens, GA, 30602, USA.
Dev Biol. 2019 Oct 1;454(1):85-95. doi: 10.1016/j.ydbio.2019.05.011. Epub 2019 May 30.
Most mosquitoes, including Aedes aegypti, only produce eggs after blood feeding on a vertebrate host. Oogenesis in A. aegypti consists of a pre-vitellogenic stage before blood feeding and a vitellogenic stage after blood feeding. Primary egg chambers remain developmentally arrested during the pre-vitellogenic stage but complete oogenesis to form mature eggs during the vitellogenic stage. In contrast, the signaling factors that maintain primary egg chambers in pre-vitellogenic arrest or that activate vitellogenic growth are largely unclear. Prior studies showed that A. aegypti females release insulin-like peptide 3 (ILP3) and ovary ecdysteroidogenic hormone (OEH) from brain neurosecretory cells after blood feeding. Here, we report that primary egg chambers exit pre-vitellogenic arrest by 8 h post-blood meal as evidenced by proliferation of follicle cells, endoreplication of nurse cells, and formation of cytoophidia. Ex vivo assays showed that ILP3 and OEH stimulate primary egg chambers to exit pre-vitellogenic arrest in the presence of nutrients but not in their absence. Characterization of associated pathways indicated that activation of insulin/insulin growth factor signaling (IIS) by ILP3 or OEH inactivated glycogen synthase kinase 3 (GSK3) via phosphorylation by phosphorylated Akt. GSK3 inactivation correlated with accumulation of the basic helix-loop-helix transcription factor Max and primary egg chambers exiting pre-vitellogenic arrest. Direct inhibition of GSK3 by CHIR-99021 also stimulated Myc/Max accumulation and primary egg chambers exiting pre-vitellogenic arrest. Collectively, our results identify GSK3 as a key factor in regulating the pre- and vitellogenic stages of oogenesis in A. aegypti.
大多数蚊子，包括埃及伊蚊，只有在吸食脊椎动物宿主的血液后才会产卵。埃及伊蚊的卵子发生包括吸血前的卵前发生阶段和吸血后的卵黄发生阶段。在卵前发生阶段，初级卵室保持发育停滞，但在卵黄发生阶段完成卵子发生，形成成熟卵子。相比之下，维持初级卵室在卵前发生停滞或激活卵黄发生生长的信号因子在很大程度上尚不清楚。先前的研究表明，埃及伊蚊雌蚊在吸血后从脑神经分泌细胞中释放胰岛素样肽 3 (ILP3) 和卵巢蜕皮激素生成激素 (OEH)。在这里，我们报告说，初级卵室在吸血后 8 小时内退出卵前发生停滞，证据是滤泡细胞增殖、滋养细胞内复制和形成细胞间纤维。离体试验表明，ILP3 和 OEH 在有营养物质的情况下刺激初级卵室退出卵前发生停滞，但在没有营养物质的情况下则不会。相关途径的特征表明，ILP3 或 OEH 通过磷酸化 Akt 激活胰岛素/胰岛素样生长因子信号 (IIS)，从而使糖原合酶激酶 3 (GSK3) 失活。GSK3 的失活与碱性螺旋-环-螺旋转录因子 Max 的积累和初级卵室退出卵前发生停滞相关。通过 CHIR-99021 直接抑制 GSK3 也刺激 Myc/Max 积累和初级卵室退出卵前发生停滞。总的来说，我们的结果确定 GSK3 是调节埃及伊蚊卵发生的卵前和卵黄发生阶段的关键因素。
