GENETIC CONTROL OF SEGMENT FORMATION

细分市场的形成是发展的最早阶段之一， 高等动物 有证据表明在早期的果蝇胚胎中 的细胞被定型为与片段相对应的模式， 细胞命运传递给后代细胞。 细胞通过这种机制 是以这种方式“确定”的是一个中心问题， 理解发展。 一个关键的方法是确定基因的产品参与了 建立这种决定的生物学过程。 我们感到关切 这里的基因是D隐性功能丧失的黑腹动物 突变导致“头尾”分割缺陷。 另外还 无尾基因作为这方面的杰出代表， 类;我们已经表明，无尾突变体形成较少，但较大的后验 胚胎中的体节和头部结构发生了变化。 我们预计 无尾+是前部正常形成所必需的， 最后的外胚层节。 提出了实验来测试 无尾动物在发育早期在特定位置活动的假说 突变体改变了胚胎的命运计划 了解基因 产品最终将通过以下方式揭示决心的本质： 段的数量和位置的控制。 此外，通过选择与或抑制 无尾突变体，我们将确定其他基因发挥作用， 片段形成。 将在第二位点寻找突变， 功能丧失使无尾占优势，或者在一个占优势的 功能获得抑制无尾突变体表型。 的遗传和 突变和基因产物的发育分析， 位点将证实它们在片段模式形成中的作用。 选择基因的基础上，他们参与无尾系统 原则上提供了一种发现所有基因的强大手段， 参与了一个特定的发展步骤。

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.