Department of Biology, University of Evansville, Evansville, IN, United States.
Department of Biological Sciences, Columbia University, New York, NY, United States.
Curr Top Dev Biol. 2020;140:55-86. doi: 10.1016/bs.ctdb.2019.10.004. Epub 2019 Nov 19.
In Drosophila, specification of the embryonic body axes requires signaling between the germline and the somatic follicle cells. These signaling events are necessary to properly localize embryonic patterning determinants in the egg or eggshell during oogenesis. There are three maternal patterning systems that specify the anterior-posterior axis, and one that establishes the dorsal-ventral axis. We will first review oogenesis, focusing on the establishment of the oocyte and nurse cells and patterning of the follicle cells into different subpopulations. We then describe how two coordinated signaling events between the oocyte and follicle cells establish polarity of the oocyte and localize the anterior determinant bicoid, the posterior determinant oskar, and Gurken/epidermal growth factor (EGF), which breaks symmetry to initiate dorsal-ventral axis establishment. Next, we review how dorsal-ventral asymmetry of the follicle cells is transmitted to the embryo. This process also involves Gurken-EGF receptor (EGFR) signaling between the oocyte and follicle cells, leading to ventrally-restricted expression of the sulfotransferase Pipe. These events promote the ventral processing of Spaetzle, a ligand for Toll, which ultimately sets up the embryonic dorsal-ventral axis. We then describe the activation of the terminal patterning system by specialized polar follicle cells. Finally, we present open questions regarding soma-germline signaling during Drosophila oogenesis required for cell identity and embryonic axis formation.
在果蝇中，胚胎体轴的特化需要生殖细胞和体滤泡细胞之间的信号传递。这些信号事件对于在卵子发生过程中正确定位胚胎模式决定因子在卵子或卵壳中是必要的。有三个母体模式系统指定前后轴，一个建立背腹轴。我们将首先回顾卵子发生，重点介绍卵母细胞和滋养细胞的建立以及滤泡细胞分化为不同亚群的模式。然后，我们描述卵母细胞和滤泡细胞之间的两个协调的信号事件如何建立卵母细胞的极性，并定位前决定因素bicoid、后决定因素oskars 和 Gurken/表皮生长因子（EGF），EGF 打破对称性以启动背腹轴的建立。接下来，我们回顾滤泡细胞的背腹不对称性如何传递给胚胎。这个过程还涉及卵母细胞和滤泡细胞之间的 Gurken-EGF 受体（EGFR）信号传递，导致 Pipe 的硫酸转移酶在腹侧受限表达。这些事件促进了 Toll 配体 Spaetzle 的腹侧加工，最终建立了胚胎的背腹轴。然后，我们描述了由专门的极性滤泡细胞激活终端模式系统。最后，我们提出了有关果蝇卵子发生中生殖细胞和体细胞信号传递对于细胞身份和胚胎轴形成的问题。
