Hydra is well known for its ability to regenerate a complete well- proportioned animal from an excised part of the body column. Extensive regeneration, transplantation and chimera experiments have established that the major patterning processes involved are a pair of developmental gradients that govern the regeneration of a head, and a second pair of gradients that control foot formation. The cell-cell interactions governing the generation, maintenance, and function of the gradients are well understood at a cell and tissue level. The next goal is to understand the molecular basis of these patterning processes.
The aim of this proposal is to begin that analysis by [1] identifying and isolating genes that are likely to be involved in these gradients, [2] developing a procedure for generating transgenic hydra to determine the role of such genes. A number of candidate genes have been identified by searching for classes of genes known to be involved in patterning events in other organisms [e.g. homeobox-containing genes, segment polarity genes and dorsal-ventral patterning genes in Drosophila]. We will focus on 7 homeobox genes which we have recently isolated. Future studies will concentrate on signalling genes. The expression patterns of candidate genes will first be examined with in situ hybridization and Northern blot analysis. More refined information will be obtained on promising genes by examining animals with normal and altered patterning processes with antibodies against the gene product of candidate genes. Complete cDNAs will be isolated for genes of interest. In a parallel effort, a novel approach for generating animals with transgenic epithelia will be worked out. When these techniques are worked out, the role of putative patterning genes will be investigated by examining the effect of their overexpression on head patterning processes. The overall significance of the effort is to help elucidate in general the set of mechanisms underlying the development of the spatial organization in animal embryos and adults. Gradients play a critical role in the development of many vertebrates and invertebrates. They occur within single cells as well as across tissues. An understanding of each type of gradient in molecular terms is necessary as part of an elucidation of the set of patterning processes.
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