Genomic action of steroid hormone in the silkworm brain during morphogenesis.

类固醇激素，20-羟基蜕皮激素（20E），触发昆虫的主要发育转变，包括蜕皮和变态。20E直接通过受体调控靶基因并执行发育。大脑在变态过程中的动态形态变化，如视叶的形成，也是由20E作用引起的。家蚕的20E水平受促胸前激素（pth）控制，而pth是由大脑中两对侧侧神经分泌细胞产生的。除了甲状旁腺激素外，大脑还产生变态所必需的肽激素。因此，昆虫大脑是昆虫发育控制的中心，大脑中的20E作用支配着胚胎后发育，包括大脑本身的形态变化。然而，在变态过程中，大脑对20E的基因组反应尚未被系统地确定。因此，我们利用一个排列了超过80%家蚕基因的微阵列和一个可诱导20e的cDNA文库，对家蚕脑中20e应答基因进行了全面的表达分析。我们专注于20E在变态过程中的直接基因组反应，从微阵列中鉴定出93个上调基因和97个下调基因，并从cDNA文库中鉴定出至少7个基因。原位杂交结果表明，这些基因的主要表达位点在产ptth细胞（PTPCs）。蜕皮激素受体复合体基因之一EcR-A也被20E上调，其mrna仅在幼虫大脑的PTPCs中检测到。这一结果表明，PTPCs是幼虫脑内主要的20e应答细胞，是昆虫变态的主细胞。

The steroid hormone, 20-hydroxyecdysone (20E), triggers the major developmental transitions of insects including molting and metamorphosis. 20E regulates target genes directly through the receptor and executes development. The dynamic morphological changes of the brain during metamorphosis such as the formation of optic lobes are also caused by 20E action. In the silkworm Bombyx mori, the 20E level is controlled by the prothoracicotropic hormone (PTTH) and PTTH is produced by the two pairs of lateral neurosecretory cells in the brain. Beside PTTH, the brain produces peptide hormones necessary for metamorphosis. The insect brain is thus the center of insect developmental control and the 20E action in the brain governs the post-embryonic development including the morphological change of the brain itself. However, the genomic response to 20E in the brain during metamorphosis has not been identified systematically.We therefore performed comprehensive expression analysis of the 20E-responsive genes of Bombyx brain with a microarray on which over 80% of total Bombyx genes are arranged and with a 20E-inducible cDNA library. We focused on the direct genomic response by 20E during metamorphosis and have identified 93 up-regulated and 97 down-regulated genes from the microarray and at least 7 genes from the cDNA library. In situ hybridization showed that major expression site of these genes characterized is at the PTTH-producing cells (PTPCs). One of the ecdysone receptor complex genes, EcR-A is also up-regulated by 20E and their mRNAs were detected exclusively in PTPCs in the larval brain. This result indicates that PTPCs are the major 20E-responsive cells in the larval brain and suggests that PTPCs are the master cells of insect metamorphosis.