Mellerick D M, Nirenberg M
Laboratory of Biochemical Genetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Dev Biol. 1995 Oct;171(2):306-16. doi: 10.1006/dbio.1995.1283.
Genes that affect the expression of the NK-2 homeobox gene were identified by comparing the patterns of NK-2 mRNA in wild-type Drosophila embryos with patterns in mutant embryos that have defects in genes that are required to establish the ventral-dorsal pattern of primordia in the early embryo. The NK-2 gene was shown to be activated by dorsal in the ventral half of the embryo during the syncytial blastoderm stage of development. However, expression of the NK-2 gene is restricted to the ventral half of the ventrolateral neurogenic anlagen and part of the procephalic region. The NK-2 gene is not expressed in the mesodermal anlage due to repression by snail, in mesectodermal cells due to repression by single-minded, or in the lateral neuroectodermal and/or dorsal epidermal anlagen due to repression mediated indirectly by decapentaplegic. Twist activates the NK-2 gene in the posterior portion of the embryo or is a coactivator with dorsal. The stripes of medial neuroectodermal cells that synthesize NK-2 mRNA are converted into clusters of neuroectodermal cells that contain NK-2 mRNA by segmentally repeated decreases in NK-2 mRNA. Medial neuroblasts, neuroblasts in the posterior portion of segments, and some ganglion mother cells and neurons express the NK-2 gene. These results suggest that the NK-2 gene receives and integrates information from ventral-dorsal and anterior-posterior gradients of gene regulators and that ventral, dorsal, anterior, and posterior boundaries of each cluster of neuroectodermal cells that express NK-2 are determined independently.
通过比较野生型果蝇胚胎中NK-2 mRNA的表达模式与突变胚胎中的表达模式，鉴定出影响NK-2同源框基因表达的基因。这些突变胚胎在早期胚胎中建立原基腹背模式所需的基因存在缺陷。研究表明，在胚胎发育的合胞体胚盘阶段，NK-2基因在胚胎腹侧的后半部分被背侧激活。然而，NK-2基因的表达仅限于腹外侧神经源性原基的腹侧一半和前脑区域的一部分。由于蜗牛蛋白的抑制作用，NK-2基因在中胚层原基中不表达；由于单-minded蛋白的抑制作用，在中胚层细胞中不表达；或者由于脱壳蛋白间接介导的抑制作用，在外侧神经外胚层和/或背侧表皮原基中不表达。扭曲蛋白在胚胎后部激活NK-2基因，或者是与背侧蛋白的共激活因子。合成NK-2 mRNA的内侧神经外胚层细胞条带通过NK-2 mRNA的分段重复减少，转化为含有NK-2 mRNA的神经外胚层细胞簇。内侧神经母细胞、节段后部的神经母细胞以及一些神经节母细胞和神经元表达NK-2基因。这些结果表明，NK-2基因接收并整合来自基因调节因子腹背和前后梯度的信息，并且每个表达NK-2的神经外胚层细胞簇的腹侧、背侧、前侧和后侧边界是独立确定的。
