Swevers Luc, Iatrou Kostas
Institute of Biology, National Centre for Scientific Research "Demokritos", Aghia Paraskevi Attikis, 153 10 Athens, Greece.
Insect Biochem Mol Biol. 2003 Dec;33(12):1285-97. doi: 10.1016/j.ibmb.2003.06.012.
The developing ovariole of the silkmoth Bombyx mori represents an excellent model for studies on the changes that occur in gene expression during the execution of long-term developmental programs. All stages of follicle development, which differ from each other by 2-2.5 h of developmental time, are organized in a single array and can be isolated simultaneously for physiological, biochemical and gene expression studies from a single animal. Recently, significant progress has been made toward the understanding of the hormonal regulation and autonomous implementation of the developmental program that governs follicular cell differentiation during oogenesis in Bombyx. In this review, the developmental career of the ovarian follicle during pharate adult development is discussed in view of the new physiological, biochemical and gene expression data that have recently accumulated. An overview is presented of the changes in expression of structural and regulatory genes and their hormonal regulation in the developing follicle during the transitions among the broad developmental periods of previtellogenesis, vitellogenesis and choriogenesis. Ovarian development in silkmoth pharate adults is induced by 20-hydroxy-ecdysone (20E) through the activation of a regulatory cascade similar to the one observed during Drosophila development. The transition from previtellogenesis to vitellogenesis corresponds to a late response to the hormone and is characterized by the induction of the expression of a unique isoform of the nuclear receptor BmHR3 and the follicular cell-specific yolk protein ESP. The transition from early to middle and late vitellogenesis and choriogenesis, on the other hand, is regulated by positively and negatively acting intra- and extra-ovarian factors. In vitro cultures of developing ovarioles reveal the requirement for the presence of an as yet unidentified growth factor(s) in the hemolymph, while the follicle developmental arrest that is observed after treatment with the ecdysone agonist tebufenozide indicates the requirement for a decline in the level of 20E. The initiation of choriogenesis is characterized by the transcriptional activation of the gene BmGATAbeta that encodes GATA transcription factors, and the chorion genes in the follicular cells. Furthermore, modulation of the activity of BmGATAbeta at the posttranscriptional level is crucial for the stage-specific activation of chorion genes during late choriogenesis. The developing ovariole of the silkmoth is, therefore, emerging as an important model for the study of insect oogenesis and the action of the steroid hormone 20E at the molecular level.
家蚕发育中的卵巢管是研究长期发育程序执行过程中基因表达变化的优秀模型。卵泡发育的各个阶段，发育时间彼此相差2 - 2.5小时，它们排列在一个单一序列中，并且可以从一只动物中同时分离出来，用于生理、生化和基因表达研究。最近，在理解家蚕卵子发生过程中调控卵泡细胞分化的发育程序的激素调节和自主执行方面取得了重大进展。在这篇综述中，鉴于最近积累的新的生理、生化和基因表达数据，讨论了在蛹期成虫发育期间卵巢卵泡的发育历程。概述了在前卵黄发生、卵黄发生和卵壳形成这几个广泛发育阶段转变过程中，发育中的卵泡中结构基因和调控基因表达的变化及其激素调节。家蚕蛹期成虫的卵巢发育是由20 - 羟基蜕皮酮（20E）通过激活一个类似于在果蝇发育过程中观察到的调控级联反应来诱导的。从前卵黄发生到卵黄发生的转变对应于对激素的晚期反应，其特征是诱导核受体BmHR3的一种独特异构体和卵泡细胞特异性卵黄蛋白ESP的表达。另一方面，从早期到中期和晚期卵黄发生以及卵壳形成的转变是由卵巢内和卵巢外的正负作用因子调节的。发育中卵巢管的体外培养揭示了血淋巴中存在一种尚未鉴定的生长因子的必要性，而在用蜕皮酮激动剂虫酰肼处理后观察到的卵泡发育停滞表明需要降低20E的水平。卵壳形成的起始特征是编码GATA转录因子的基因BmGATAbeta和卵泡细胞中的卵壳基因的转录激活。此外，在转录后水平对BmGATAbeta活性的调节对于卵壳形成后期卵壳基因的阶段特异性激活至关重要。因此，家蚕发育中的卵巢管正在成为研究昆虫卵子发生和类固醇激素20E在分子水平上作用的重要模型。
