Embryonic expression and function of the Drosophila helix-loop-helix gene, extramacrochaetae.

extramacrochaetae (emc) encodes a HLH protein that functions as a regulator of sensory organ precursor formation by virtue of its ability to form inactive heterodimers with the bHLH products of the achaete-scute complex (AS-C) and/or daughterless (da) genes. Although zygotic emc function is required for embryonic viability, its role in embryogenesis is not well understood. We describe here the distribution of emc transcripts during embryonic development. We also show that emc transcript is maternally contributed. Finally, we demonstrate that emc function is required for normal midgut and Malpighian tubule development. These results suggest that negative regulation by emc may be a common feature of developmental processes involving da, the AS-C and possibly other helix-loop-helix proteins.