Terashima J, Takaki K, Sakurai S, Bownes M
Institute of Cell and Molecular Biology, University of Edinburgh, Darwin Building, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, UK.
J Endocrinol. 2005 Oct;187(1):69-79. doi: 10.1677/joe.1.06220.
Drosophila egg production depends upon the nutritional available to females. When food is in short supply, oogenesis is arrested and apoptosis of the nurse cells is induced at mid-oogenesis via a mechanism that is probably controlled by ecdysteroid hormone. We have shown that expression of some ecdysone-response genes is correlated with apoptosis of egg chambers. Moreover, ecdysteroid injection and application of juvenile hormone induces and suppresses the apoptosis, respectively. In this study, we investigated which tissues show increases in the concentration of ecdysteroids under nutritional shortage to begin to link together nutrient intake, hormone regulation and the choice between egg development or apoptosis made within egg chambers. We measured ecdysteroid levels in the whole body, ovaries and haemolymph samples by RIA and found that the concentration of ecdysteroid increased in all samples. This contributes to the idea that nutritional shortage leads to a rapid high ecdysteroid concentration within the fly and that the high concentration induces apoptosis. Low concentrations of ecdysteroid are essential for normal oogenesis. We suggest there is threshold concentration in the egg chambers and that apoptosis at mid-oogenesis is induced when the ecdysteroid levels exceed the threshold. Starvation causes the ovary to retain the ecdysteroid it produces, thus enabling individual egg chambers to undergo apoptosis and thus control the number of eggs produced in relation to food intake.
果蝇的产卵量取决于雌性果蝇可获得的营养物质。当食物供应短缺时，卵子发生会停滞，并且在卵子发生中期，通过一种可能受蜕皮甾体激素控制的机制诱导滋养细胞凋亡。我们已经表明，一些蜕皮激素反应基因的表达与卵室凋亡相关。此外，注射蜕皮甾体激素和应用保幼激素分别诱导和抑制凋亡。在本研究中，我们调查了在营养缺乏情况下哪些组织中蜕皮甾体激素浓度会升高，以便将营养摄入、激素调节以及卵室内卵子发育或凋亡的选择联系起来。我们通过放射免疫分析法测量了全身、卵巢和血淋巴样本中的蜕皮甾体激素水平，发现所有样本中蜕皮甾体激素浓度均升高。这支持了营养缺乏导致果蝇体内迅速出现高浓度蜕皮甾体激素且高浓度诱导凋亡的观点。低浓度的蜕皮甾体激素对于正常的卵子发生至关重要。我们认为在卵室中存在一个阈值浓度，当蜕皮甾体激素水平超过该阈值时，在卵子发生中期就会诱导凋亡。饥饿会使卵巢保留其产生的蜕皮甾体激素，从而使单个卵室能够发生凋亡，进而根据食物摄入量控制产卵数量。
