Ferreiro B, Kintner C, Zimmerman K, Anderson D, Harris W A
Department of Biology, University of California San Diego, La Jolla 92093-0357.
Development. 1994 Dec;120(12):3649-55. doi: 10.1242/dev.120.12.3649.
Neural development in Drosophila is promoted by a family of basic helix-loop-helix (bHLH) transcription factors encoded within the Achaete Scute-Complex (AS-C). XASH-3, a Xenopus homolog of the Drosophila AS-C genes, is expressed during neural induction within a portion of the dorsal ectoderm that gives rise to the neural plate and tube. Here, we show that XASH-3, when expressed with the promiscuous binding partner XE12, specifically activates the expression of neural genes in naive ectoderm, suggesting that XASH-3 promotes neural development. Moreover, XASH-3/XE12 RNA injections into embryos lead to hypertrophy of the neural tube. Interestingly, XASH-3 misexpression does not lead to the formation of ectopic neural tissue in ventral regions, suggesting that the domain of XASH proneural function is restricted in the embryo. In contrast to the neural inducer noggin, which permanently activates the NCAM gene, the activation of neural genes by XASH-3/XE12 is not stable in naive ectoderm, yet XASH-3/XE12 powerfully and stably activates NCAM, Neurofilament and type III beta-tubulin gene expression in noggin-treated ectoderm. These results show that the XASH-3 promotes neural development, and suggest that its activity depends on additional factors which are induced in ectoderm by factors such as noggin.
果蝇的神经发育由achaete scute复合体（AS-C）中编码的一类碱性螺旋-环-螺旋（bHLH）转录因子促进。XASH-3是果蝇AS-C基因的非洲爪蟾同源物，在神经诱导过程中，在背侧外胚层的一部分中表达，该部分会形成神经板和神经管。在这里，我们表明，当与混杂结合伴侣XE12一起表达时，XASH-3能特异性激活未分化外胚层中神经基因的表达，这表明XASH-3促进神经发育。此外，向胚胎中注射XASH-3/XE12 RNA会导致神经管肥大。有趣的是，XASH-3的错误表达不会导致腹侧区域形成异位神经组织，这表明XASH神经原功能域在胚胎中受到限制。与能永久激活NCAM基因的神经诱导因子头蛋白不同，XASH-3/XE12对神经基因的激活在未分化外胚层中不稳定，但XASH-3/XE12能在头蛋白处理过的外胚层中强有力且稳定地激活NCAM、神经丝和III型β-微管蛋白基因的表达。这些结果表明XASH-3促进神经发育，并表明其活性依赖于由头蛋白等因子在外胚层中诱导产生的其他因子。
