Shiomi Kunihiro, Fujiwara Yoshihiro, Atsumi Tsutomu, Kajiura Zenta, Nakagaki Masao, Tanaka Yoshiaki, Mizoguchi Akira, Yaginuma Toshinobu, Yamashita Okitsugu
Faculty of Textile Science and Technology, Shinshu University, Nagano, Japan.
FEBS J. 2005 Aug;272(15):3853-62. doi: 10.1111/j.1742-4658.2005.04799.x.
Prothoracicotropic hormone (PTTH) plays a central role in controlling molting, metamorphosis, and diapause termination in insects by stimulating the prothoracic glands to synthesize and release the molting hormone, ecdysone. Using Autographa californica nucleopolyhedrovirus (AcNPV)-mediated transient gene transfer into the central nervous sytem (CNS) of the silkworm, Bombyx mori, we identified two cis-regulatory elements that participate in the decision and the enhancement of PTTH gene expression in PTTH-producing neurosecretory cells (PTPCs). The cis-element mediating the enhancement of PTTH gene expression binds the transcription factor Bombyx myocyte enhancer factor 2 (BmMEF2). The BmMEF2 gene was expressed in various tissues including the CNS. In brain, the BmMEF2 gene was expressed at elevated levels in two types of lateral neurosecretory cells, namely PTPCs and corazonin-like immunoreactive lateral neurosecretory cells. Overexpression of BmMEF2 cDNA caused an increase in the transcription of PTTH. Therefore, BmMEF2 appears to be particularly important in the brain where it is responsible for the differentiation of lateral neurosecretory cells, including the enhancement of PTTH gene expression. This is the first report to identify a target gene of MEF2 in the invertebrate nervous system.
促前胸腺激素（PTTH）通过刺激前胸腺合成并释放蜕皮激素（ecdysone），在控制昆虫的蜕皮、变态和滞育终止过程中发挥核心作用。利用苜蓿银纹夜蛾核型多角体病毒（AcNPV）介导的瞬时基因转移技术，将其导入家蚕（Bombyx mori）的中枢神经系统（CNS），我们鉴定出了两个顺式调控元件，它们参与了PTTH基因在PTTH分泌性神经分泌细胞（PTPCs）中的表达调控以及表达增强过程。介导PTTH基因表达增强的顺式元件可与转录因子家蚕肌细胞增强因子2（BmMEF2）结合。BmMEF2基因在包括中枢神经系统在内的多种组织中均有表达。在脑中，BmMEF2基因在两种类型的侧神经分泌细胞中高表达，即PTPCs和类促心肽免疫反应性侧神经分泌细胞。BmMEF2 cDNA的过表达导致PTTH转录增加。因此，BmMEF2在脑中似乎尤为重要，它负责侧神经分泌细胞的分化，包括增强PTTH基因的表达。这是首次在无脊椎动物神经系统中鉴定出MEF2的靶基因的报告。
