Stage-specific plasticity in ovary size is regulated by insulin/insulin-like growth factor and ecdysone signalling in Drosophila

Animals from flies to humans adjust their development in response to environmental conditions through a series of developmental checkpoints, which alter the sensitivity of organs to environmental perturbation. Despite their importance, we know little about the molecular mechanisms through which this change in sensitivity occurs. Here we identify two phases of sensitivity to larval nutrition that contribute to plasticity in ovariole number, an important determinant of fecundity, in Drosophila melanogaster. These two phases of sensitivity are separated by the developmental checkpoint called “critical weight”; poor nutrition has greater effects on ovariole number in larvae before critical weight than after. We find that this switch in sensitivity results from distinct developmental processes. In precritical weight larvae, poor nutrition delays the onset of terminal filament cell differentiation, the starting point for ovariole development, and strongly suppresses the rate of terminal filam...从果蝇到人类的诸多动物，均可通过一系列发育检查点（developmental checkpoint）响应环境条件以调控自身发育进程，此类检查点可改变器官对环境扰动的敏感性。尽管此类检查点功能至关重要，但目前学界对其介导敏感性改变的分子机制仍知之甚少。本研究在黑腹果蝇（Drosophila melanogaster）中，鉴定出两类针对幼虫营养的敏感性阶段，这些阶段参与调控卵巢管数目（ovariole number）的表型可塑性——而卵巢管数目是影响繁殖力（fecundity）的核心指标。这两类敏感性阶段以名为“临界体重（critical weight）”的发育检查点为界：相较于临界体重达成后的幼虫，临界体重达成前的幼虫若遭遇营养匮乏，其卵巢管数目受到的影响更为显著。我们发现，这种敏感性的转变源自不同的发育进程：在临界体重前的幼虫体内，营养匮乏会延迟终丝细胞分化的启动——而终丝细胞分化是卵巢管发育的起始环节，并会显著抑制终丝（terminal filament）的生成速率……