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

类固醇激素20-羟基蜕皮激素（20 E）触发昆虫的主要发育转变，包括蜕皮和变态。20 E通过受体直接调控靶基因并执行发育。变态期间大脑的动态形态变化，例如视叶的形成，也是由20 E作用引起的。在家蚕中，20 E水平由促前胸腺激素（PTTH）控制，PTTH由大脑中的两对侧神经分泌细胞产生。除了PTTH，大脑还产生变态所必需的肽激素。因此，昆虫脑是昆虫发育控制的中心，脑中的20 E作用控制着胚胎后发育，包括脑本身的形态变化。然而，在变态过程中的脑20 E的基因组反应还没有得到系统的鉴定，因此，我们进行了全面的表达分析的20 E-反应基因的基因芯片上排列的总的20 E-诱导的cDNA文库的20 E-诱导的20 E-反应基因的20 E-诱导的cDNA文库。我们重点研究了20 E在变态过程中的直接基因组反应，并从基因芯片中鉴定了93个上调基因和97个下调基因，从cDNA文库中鉴定了至少7个基因。原位杂交结果表明，这些基因的主要表达位点是在PTTH产生细胞（PTPC）。EcR-A是蜕皮激素受体复合物基因之一，也被20 E上调，并且其mRNA仅在幼虫脑中的PTPC中检测到。这一结果表明，PTPC是幼虫脑中主要的20 E-反应细胞，并建议PTPC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.