CHARACTERIZATION OF HOMEO BOX HOMOLOGIES IN THE LEECH

最近已经证明存在直接的dna序列。 果蝇几个同源异型基因之间的同源性。这一地区一直是 被称为Homeo Box，已经被证明是保守的，大约60 氨基酸残基序列。猪瘟病毒基因组DNA的杂交研究 各种其他物种带有含有果蝇同源盒的探针 表明与Homeo盒同源的区域在进化上是 保守的。杂交技术也可用于分离 一些在青蛙、老鼠和人类中包含这一区域的基因。 因为含有同源异型盒的果蝇基因会影响 发展过程，特别是分段和分段 分化，有人提出同源异型盒也可以是一个 在其他物种中寻找这类基因的标记。一群动物，在其中进行一项测试 这一想法的最合适的方法就是水蛭。水蚤，就像 所有其他环节动物和昆虫一样，都表现出明显的节段性 他们身体的组织。目前的进化论认为，昆虫 是环节动物祖先的后代，这表明 昆虫的同源异型基因是由相应的环节动物基因进化而来的。 此外，我们的初步观察表明，水蚤也有 含有与果蝇同源基因盒交叉杂交的区域的基因。 在这里提出的项目的目的是识别和分离这些基因 在几种水蚤中，并确定它们的空间和 表达的时间模式与果蝇的相似 含有同源基因盒子的基因。我们将首先实现这一目标 同源异源盒杂交区域近似数的确定 经Southern印迹分析。然后我们将确定程度 通过对水蚤DNA区域进行测序，确定与Homeo盒的同源性 感兴趣，并将通过Northern分析来表征他们的记录。 最后，我们将在连续的组织切片上进行原位杂交。 用来评估水蚤胚胎表达的时空模式 已确定的水蛭基因。特别是，我们将研究 这些基因在个体水平上，识别了水蚤中的神经元 CNS，以确定差异基因表达是否与 神经元表型的节段性分化 特色化的。这次调查的结果应该有重要的意义 关系到我们对控制早期的基因进化的理解 这些基因的发展及其在表型发生中的作用 中枢神经系统的异质性。

It has been recently demonstrated that there is direct DNA sequence homology between several Drosophila homeotic genes. This region has been called the homeo box and has been shown to code for a conserved, about 60 amino acid residue sequence. Cross-hybridization of genomic DNA from various other species with probes containing the Drosophila homeo box has suggested that regions homologous to the homeo box are evolutionarily conserved. Cross-hybridization has also been useful in the isolation of some of the genes that contain this region in frogs, mice and humans. Because the Drosophila genes that contain the homeo box affect developmental processes, in particular segmentation and segmental differentiation, it has been proposed that the homeo box could also be a marker for such genes in other species. A group of animals in which a test of this idea would be particularly appropriate are leeches. Leeches, like all other annelids and like the insects, display an obvious segmental organization of their bodies. Current evolutionary theory has the insects descending from an annelid ancestor, suggesting the possibility that the insect homeotic genes have evolved from corresponding annelid genes. Furthermore, our preliminary observations indicate that leeches also have genes that contain regions which cross-hybridize with the fly homeo box. The aim of the project proposed here is to identify and isolate such genes in a few species of leeches, and to determine whether their spatial and temporal patterns of expression are similar to those of the Drosophila genes that contain the homeo box. We will pursue this goal by first determining the approximate number of homeo box cross-hybridizing regions in the leech by Southern blot analysis. We will then determine the degree of homology with the homeo box by sequencing the regions of leech DNA of interest and will characterize their transcripts by Northern analysis. Finally, we will do in situ hybridization on serial tissue sections of leech embryos to assess the spatial and temporal patterns of expression of the identified leech genes. In particular, we will study the expression of these genes at the level of individual, identified neurons in the leech CNS, to determine whether differential gene expression correlates with the segmental differentiation of neuronal phenotypes that we have characterized. The results of this investigation should have a significant bearing on our understanding of the evolution of genes that control early development and of the role of such genes in the genesis of phenotypic heterogeneity in the CNS.