Mann R S
Department of Biochemistry and Molecular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Development. 1994 Nov;120(11):3205-12. doi: 10.1242/dev.120.11.3205.
The homeotic genes of Drosophila are expressed in overlapping domains along the anterior-to-posterior axis and specify the distinct morphological patterns of each parasegment. Within single parasegments, the levels of homeotic gene expression are often modulated, in part because of cross-regulation by other homeotic gene products. However, the functional significance of different levels of homeotic gene expression is unclear. Here modulations in Ultrabithorax (Ubx) expression within parasegment 6 are examined. Specifically, Ubx is shown to be down-regulated in the posterior compartment of this parasegment by engrailed (en). The significance of Ubx repression by en was demonstrated by characterizing the expression of the Ubx target gene, Distal-less (Dll). In the posterior compartment of parasegment 6, Dll is normally expressed in a small cluster of cells. If Ubx is expressed uniformly via a heat-shock promoter, Dll is inappropriately repressed in these posterior compartment cells. In the anterior compartment of parasegment 6, Dll is normally repressed by high levels of Ubx. However, if en is expressed uniformly via a heat-shock promoter, Ubx is repressed and Dll is derepressed. Because Dll is required for the development of larval sensory structures, these results demonstrate that en-mediated repression of Ubx in the posterior compartment is necessary for the morphology of parasegment 6. Thus, different levels of homeotic gene expression can be important for their segmental patterning functions.
果蝇的同源异型基因沿前后轴在重叠区域表达，并指定每个副节段独特的形态模式。在单个副节段内，同源异型基因的表达水平常常受到调控，部分原因是其他同源异型基因产物的交叉调控。然而，同源异型基因不同表达水平的功能意义尚不清楚。本文研究了副节段6内超双胸（Ubx）基因表达水平的调控。具体而言，研究发现Ubx在该副节段的后区室中被 engrailed（en）基因下调。通过对Ubx靶基因 Distal-less（Dll）的表达特征进行分析，证明了en对Ubx的抑制作用具有重要意义。在副节段6的后区室中，Dll通常在一小簇细胞中表达。如果通过热休克启动子使Ubx均匀表达，这些后区室细胞中的Dll就会被不恰当地抑制。在副节段6的前区室中，Dll通常被高水平的Ubx抑制。然而，如果通过热休克启动子使en均匀表达，Ubx就会被抑制，Dll则会解除抑制。由于Dll是幼虫感觉结构发育所必需的，这些结果表明，en介导的对后区室中Ubx的抑制对于副节段6的形态形成是必要的。因此，同源异型基因不同的表达水平对于其节段模式形成功能可能很重要。
