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The endocrine mechanisms that determine the timing of initiation of larval-pupal transformation

决定幼虫-蛹转化开始时间的内分泌机制

基本信息

批准号：
14540613
负责人：
MIZOGUCHI Akira
金额：
$ 1.98万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

When final instar larvae of insects have fully grown, their brain secretes the prothoracicotropic hormone (PTTH) to stimulate the prothoracic glands, which in turn secrete ecdysteroid leading to initiation of larval-pupal transformation. In the present study, the mechanism that leads to this surge of PTTH at the mid fifth instar of the silkmoth, Bombyx mori was analyzed. Since small peaks of hemolymph titers of PTTH and ecdysteroids were detected at the same time on the day before the occurrence of PTTH surge, we hypothesized that this rise in ecdysteroid titer affects the brain enhancing its PTTH secretory activity. When a small dose of ecdysteroid was injected to larvae two days before the occurrence of PTTH surge, indicating that ecdysteroid is responsible for the increase in PTTH secretory activity of the brain. This is the first to demonstrate the positive feedback regulation of the brain by the prothoracic glands. We also studied the mechanisms by which the prothoracic gland activity is regulated during early fifth instar using a newly developed long-term in vitro culture system of the gland. This study revealed that the prothoracic gland of fourth instar larvae is inactivated by ecdysteroids released by the gland at mid fourth instar through negative feedback mechanism and that, after ecdysis to teh fifth instar, the gland is spontaneously reactivated to some extent without stimulation by PTTH. We speculate that the prothoracic glands of fifth instar larvae gradually increase their ecdysone secretory activity and PTTH sensitivity in accord with larval growth so that the glands of fully grown larvae can secrete enough amounts of ecdysone, in response to a small secretion of PTTH, to stimulate the brain.

当昆虫的末龄幼虫完全生长时，它们的大脑分泌促前胸激素（PTTH）以刺激前胸腺，前胸腺继而分泌蜕皮类固醇，导致幼虫-蛹转化的开始。本研究对家蚕五龄中期PTTH高峰的形成机制进行了分析。由于小峰的血淋巴滴度的PTTH和蜕皮甾类激素的检测在同一时间的PTTH激增的发生前一天，我们推测，蜕皮甾类激素滴度的上升影响大脑增强其PTTH分泌活性。在PTTH峰出现前2天注射小剂量蜕皮激素，说明蜕皮激素是脑PTTH分泌活性增加的原因。这是第一次证明大脑的正反馈调节的前胸腺。我们还研究了前胸腺活动的调节机制，在五龄早期使用一个新开发的长期体外培养系统的腺体。本研究表明，四龄幼虫前胸腺在四龄中期通过负反馈机制被蜕皮激素灭活，蜕皮至五龄后，在不受PTTH刺激的情况下，前胸腺又在一定程度上自发激活。我们推测，五龄幼虫的前胸腺逐渐增加其蜕皮激素分泌活性和PTTH的敏感性在雅阁的生长，使腺体的完全成熟的幼虫可以分泌足够量的蜕皮激素，以响应少量的分泌PTTH，刺激大脑。