Gonadogenesis in the Drosophila embryo is a complex process involving numerous cellular migratory steps and cell-cell interactions. The mechanisms guiding germ cells to move through, recognize and adhere to specific cell types are poorly understood. In order to identify genes that are required for these processes, we have conducted an extensive mutagenesis of the third chromosome and screened for mutations disrupting germ cell migration at any point in embryonic development. Phenotypic analysis of these mutants demonstrates that germ cell migration can be broken down into discrete developmental steps, with each step requiring a specific set of genes. Many of these genes are involved in the development of gonadal mesoderm, the tissue that associates with germ cells to form the embryonic gonad. Moreover, mutations that we isolated affecting embryonic patterning as well as germ cell migration suggest that the origin of gonadal mesoderm lies within the eve domain of the developing mesoderm.

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