Lee Y M, Park T, Schulz R A, Kim Y
Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1997 Jul 11;272(28):17531-41. doi: 10.1074/jbc.272.28.17531.
NK-4, also called msh2 and tinman, encodes a homeodomain transcription factor that is required for the development of the dorsal mesoderm and its derivatives in the Drosophila embryo. Genetic analyses indicate that NK-4 resides downstream of the mesodermal determinant twist, which encodes a basic helix-loop-helix-type transcription factor. However, the regulation of NK-4 by twist remains poorly understood. Using expression assays in cultured cells and transgenic flies, we show that two distinct clusters of E-box regulatory sequences, present upstream of the NK-4 gene, mediate NK-4 expression in the visceral mesoderm. These elements are conserved between the Drosophila melanogaster and Drosophila virilis NK-4 genes and serve as binding sites for Twist (E1 cluster) and NK-4 (E2 cluster) proteins. In cultured cells, Twist and NK-4 binding results in activation of NK-4 gene expression. In transgenic animals, the E1 and E2 clusters are functionally connected, and both elements are required for NK-4 activation in cells of the visceral mesoderm and also for NK-4 repression in cells of the somatic musculature. These results demonstrate that NK-4 is a direct transcriptional target for Twist and its own gene product in visceral mesodermal cells, supporting the idea that twist and NK-4 function in the subdivision of the mesoderm during Drosophila embryogenesis.
NK-4，也称为msh2和tinman，编码一种同源域转录因子，该因子是果蝇胚胎中背侧中胚层及其衍生物发育所必需的。遗传分析表明，NK-4位于中胚层决定因子twist的下游，twist编码一种碱性螺旋-环-螺旋型转录因子。然而，twist对NK-4的调控仍知之甚少。通过在培养细胞和转基因果蝇中进行表达分析，我们发现NK-4基因上游存在两个不同的E-box调控序列簇，它们介导NK-4在内脏中胚层中的表达。这些元件在黑腹果蝇和粗壮果蝇的NK-4基因之间保守，并作为Twist（E1簇）和NK-4（E2簇）蛋白的结合位点。在培养细胞中，Twist和NK-4的结合导致NK-4基因表达的激活。在转基因动物中，E1和E2簇在功能上相互连接，这两个元件对于NK-4在内脏中胚层细胞中的激活以及在体壁肌肉组织细胞中的抑制都是必需的。这些结果表明，NK-4是内脏中胚层细胞中Twist及其自身基因产物的直接转录靶标，支持了twist和NK-4在果蝇胚胎发育过程中参与中胚层细分的观点。
