ANALYSIS OF A MURINE HOMEOBOX LOCUS

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The identification of the murine Hox gene system, which plays a crucial role in establishing the body plan, was guided by the paradigm predicting essential conservation of certain key processes of development among most metazoans. This paradigm was substantiated by studies indicating that the murine Hox gene system parallels the homeotic gene system of Drosophila, HOM-C, in structure, clustered organization, antero-posterior expression patterns, and presumably in its function of assigning positional identities. Accordingly, this project's long term objectives are: (i) establishing to which extent the murine Hoxc locus fits this premise and (ii) understanding some of the transcriptional control mechanisms that facilitate the distinct spatio-temporally restricted patterns of Hox gene expression. The following specific aims define a strategy for achieving these goals: (1) Putative morphogenetic control functions of the Hoxc-10 gene will be analyzed by targeted misexpression in transgenic mice using heterologous region-specific control elements. Based on the unique spatially restricted expression pattern of Hoxc-10 during mouse development, its presumptive domain of function is restricted to posterior body regions including the developing hindlimb, pelvic girdle and urogenital system. Accordingly, these studies promise to elucidate essential aspects of putative developmental control functions specific for Hoxc-10 and contribute to our general understanding of Hox gene function. (2) Proper development requires precisely orchestrated Hox gene expression patterns. These patterns are presumably mediated by complex cis-acting regulatory elements. The isolation of regulatory elements required for the correct expression of Hoxc-9 and -10 will be performed by deletion analyses of pertinent Hoxc/lacZ reporter gene constructs in transgenic mice. This will represent all important first step in the analysis of the molecular mechanisms controlling transcription of Hoxc-9 and -10, thus contributing to our understanding of the establishment of regional specificities of gene expression, a key problem of development. (3) The hypothesis that the remarkable similarities in the distinct, serially arranged antero-posterior expression patterns of Hox and HOM-C genes indicate highly conserved transcriptional control mechanisms for specifying positional identities, will be tested by examining functional conservation of HOM-C positional control elements and HOM-C responsive elements in transgenic mice utilizing LacZ reporter gene constructs. These experiments are aimed at identifying minimal elements that function universally in establishing region-specific gene expression along the antero-posterior embryonic axis. This project promises to contribute to an understanding of the molecular mechanisms underlying certain congenital malformations and the molecular actions of teratogenic substances during human development. Following the premise that Hox genes specify cellular identities, these studies may also have an impact on our understanding of diseases involving a loss of such identities as typified in cancer.