MOLECULAR GENETICS OF SEGMENT IDENTITY

复杂有机体的形态发生取决于一种 错综复杂的遗传层次结构为单个细胞提供 位置和细胞命运信息。在果蝇中，同源异型 选择器基因在这个层次结构中起着核心作用，因为它们 解读位置信息并决定细胞命运。这些基因 在包括人类在内的许多动物中都有高度保守的同源物， 这表明他们对果蝇的分析可能是 也了解脊椎动物的发育。分子解剖 脊椎动物的发展，反过来将提供对人类的洞察 疾病，包括出生缺陷和各种癌症，这些疾病似乎 是由于在执行这种遗传层次结构时的错误造成的。 果蝇是一种特别适合研究这一现象的生物。 层次结构，因为它具有实验性的多功能性，尤其是在 关于它的分子生物学和遗传学。同源异型选择器 基因为这些研究提供了一个有吸引力的入口，因为 已有的遗传和分子信息量。这个 这些基因的产物都含有DNA结合的同源结构域和ACT， 至少部分地通过调节下游靶基因的转录 基因。这里提出的实验有两个相辅相成的目标： 识别和鉴定受同源异型体调控的靶基因 选择器基因，超双胸，并详细了解同源异型 选择器蛋白调节靶基因的表达。第一个目标将是 被以两种方式接近。一种消减杂交方法已经 成功分离出20个由极端细菌基因诱导的基因 产品。其中三个基因似乎是真正的下游靶点。 基因，并将进行详细研究。基因方法涉及到 分离增强或抑制的显性突变 超生物胸腔诱导的同源异型转化。在这种情况下发现的基因 将对筛查进行检查，以确定它们是否真的是超双胸 靶基因。如果它们看起来是真正的靶基因，它们将是 通过DNA测序，进一步确定它们在体内的特征 空间和时间表达模式，并检测它们的遗传 与其他同源异型突变的相互作用。这方面的第二个目标 建议更好地了解同源异型选择器蛋白是如何调节的 靶基因表达。IBIS将通过突变来完成 超双胸腔蛋白，并使用体内测试来研究它们 测量同源异型蛋白的功能。已经有检测方法可用于 研究胚胎发育所需的功能。除了……之外 这些，新的活体检测方法将被开发来测量超双胸 成体形态发生所需的功能。这些活体研究将 与使用测量In的新分析方法的实验相平行 突变的超生物胸膜蛋白的体外DNA结合特性。这些 实验将确定特定的突变是否会影响紫外线胸腔 通过影响它们与DNA结合的能力或通过影响某些 其他性质，如特定的蛋白质-蛋白质相互作用。

The morphogenesis of a complex organism depends upon the execution of an intricate genetic hierarchy that provides individual cells with positional and cell fate information. In Drosophila the homeotic selector genes play a central role in this hierarchy because they interpret positional information and determine cell fate. These genes have highly conserved homologs in many animals, including humans, suggesting that their analysis in Drosophila may be a key to understanding vertebrate development as well. The molecular dissection of vertebrate development will, in turn, provide insights into human diseases, including birth defects and various cancers, that appear to result from mistakes in the execution of this genetic hierarchy. Drosophila is an especially well suited organism in which to study this hierarchy because of its experimental versatility, particularly with regard to its molecular biology and genetics. The homeotic selector genes provide an attractive entry into these studies because of the large amount of genetic and molecular information already available. The products of these genes all contain the DNA-binding homeodomain and act, at least in part, by regulating the transcription of downstream target genes. The experiments proposed here have two complementary goals: to identify and characterize target genes that are regulated by the homeotic selector gene, Ultrabithorax, and to understand in detail how homeotic selector proteins regulate target gene expression. The first goal will be approached in two ways. A subtractive hybridization approach has succeeded in isolating 20 genes that are induced by Ultrabithorax gene products. Three of these genes appear to be bona fide downstream target genes and will be studied in detail. A genetic approach involves isolating dominant mutations that enhance or suppress Ultrabithorax-induced homeotic transformations. Genes identified in this screen will be examined to determine if they are indeed Ultrabithorax target genes. If they appear to be true target genes they will be further characterized by DNA sequencing, determining their in vivo spatial and temporal expression patterns, and examining their genetic interactions with other homeotic mutations. The second goal of this proposal is to better understand how homeotic selector proteins regulate target gene expression. Ibis will be accomplished by making mutant Ultrabithorax proteins and studying them using in vivo assays that measure homeotic protein functions. Assays are already available for studying functions required during embryonic development. In addition to these, new in vivo assays will be developed to measure Ultrabithorax functions required for adult morphogenesis. These in vivo studies will be paralleled by experiments utilizing new assays that measure the in vitro DNA binding properties of mutant Ultrabithorax proteins. These experiments will determine if particular mutations affect Ultrabithorax functions by affecting their ability to bind DNA or by affecting some other property, such as specific protein-protein interactions.