Transcription of the neurogenic gene mastermind during Drosophila development.

The neurogenic loci of Drosophila encode the components of a cell communication pathway that operates during multiple developmental stages and in numerous tissues. Activation of the pathway is required for inhibitory interactions, during partitioning of cells into alternative pathways of differentiation. Genetic studies of these loci have demonstrated numerous interactions, suggesting a close relationship among the gene products; molecular studies have corroborated some of these ideas. The mastermind (mam) locus shows genetic interactions with several neurogenic loci, yet its role in this pathway is unknown. We have analyzed mam transcription and further characterized the phenotype associated with mam alleles. mam is widely expressed in patterns overlapping those of other neurogenic loci during embryonic and postembryonic development; embryonic transcription is not dependent upon function of neurogenic genes. mam transcription is widespread during most of embryogenesis; however, late embryonic expression appears limited to the nervous system. Central nervous system expression persists at high levels during larval and pupal stages. Widespread transcription is also observed in ovaries and imaginal discs, with enhanced levels just anterior to the morphogenetic furrow of the eye disc. Phenotypic analyses of mam mutations demonstrate a broad phenotypic range and suggest that particular alleles disturb features of the CNS unrelated to neural overgrowth.