A basic-helix-loop-helix protein expressed in precursors of Drosophila longitudinal visceral muscles.

Basic-helix-loop-helix (bHLH) transcription factors are involved in the control of many developmental processes in vertebrates and invertebrates. The HLH domain mediates formation of homo- or heterodimers. We have taken advantage of these dimerisation properties to identify a novel Drosophila HLH protein using the yeast two-hybrid system. Expression of bHLH54F at the blastoderm stage is restricted to a small subpopulation of mesodermal cells near the posterior pole. During germ band retraction these cells spread along the future midgut region. Later bHLH54F-expressing cells make up the longitudinal portion of the visceral musculature. Characterisation of this expression pattern demonstrates that precursors of the outer, longitudinal muscles of the midgut are distinct in origin and morphology from precursors of the inner, circular muscles.