GENETIC CONTROL OF SEGMENT FORMATION

语段的形成是语言发展的最早阶段之一 高等动物。在果蝇早期胚胎中有证据表明， 的细胞被承诺成与片段相对应的模式， 细胞命运传递给后代细胞。细胞的作用机制 以这种方式被“下定决心”是 理解发展。 一种关键的方法是识别其产物参与 建立这种决心的生物学过程。我们对此感到担忧 这里是黑腹金龟子的基因，它的隐性功能丧失 突变会导致“头和尾”的分割缺陷。具体来说，我们 以无尾基因为杰出代表的 我们已经证明了无尾突变体形成的后部更少但更大 胚胎中的片段和头部结构被改变。我们预计 无尾+是正常的前部和后部形成所必需的 最后面的外胚层裂片。建议进行实验，以测试 无尾在特定位置发育早期的假说 变种人改变了胚胎的命运计划。了解这种基因 产品最终将通过以下方式阐明决定的本质 对分段的数量和位置的控制。 此外，通过选择与之相互作用或抑制的突变 无尾突变体，我们将确定其他基因在 线段形成。将在第二个地点寻找突变，其中 功能丧失使无尾占优势，或在占优势的地方 功能获得抑制无尾突变表型。基因和 在此秒内编码的突变和基因产物的发育分析 这些部位将证实它们在片段图案形成中的作用。 根据基因参与无尾系统进行基因选择 原则上提供了一种强大的方法来发现所有 都参与了特定的发育步骤。

Segment formation is one of the earliest stages in the development of higher animals. There is evidence in early Drosophila embryos that groups of cells ar committed into patterns that correspond to segments and that cell fates are transmitted to progeny cells. The mechanism by which cells are "determined" in this way is one of the central problems in understanding development. A key approach is to identify genes whose products are involved in the biological process of establishing this determination. We are concerned here with genes in D. melanogaster whose recessive loss-of-function mutations lead to "head 'n tail" segmentation defects. Specifically we have focused on the gene tailless as the outstanding representative of this class; we have shown that tailless mutants form fewer but larger posterior segments in the embryo and that head structures are altered. We expect that tailless+ is required for normal formation of the anterior and posterior-most ectodermal segments. Experiments are proposed to test the hypotheses that tailless acts early in development at specific locations and that the mutant alters the embryonic fate plan. Knowing the gene product will ultimately throw light on the nature of determination through the control of the number and locations of segments. In addition, by means of selecting mutations that interact with or suppress the tailless mutant, we will identify other genes that play a role in segment formation. Mutations will be sought at second sites where a loss-of-function makes tailless dominant, or where a dominant gain-of-function suppresses the tailless mutant phenotype. The genetic and developmental analysis of mutations and gene products coded at such second sites will corroborate their role in segment pattern formation. Selecting genes on the basis of their involvement with the tailless system in principle provides a powerful means of discovering all of the genes that are involved in a specific developmental step.