Ventral neuroblasts and the Heartless FGF receptor are required for musclefounder cell specification in Drosophila

Muscle founder cells are uniquely specified cells that fuse with neighborin g myoblasts to generate the complex pattern of body wall muscles in the Dro sophila embryo. We have investigated the positional specification of founde r cells for ventral oblique muscles, marked by the restricted expression of tinman RNA and the activity of a D-mef2 enhancer. The formation of these v entral myoblasts requires the function of the Heartless FGF receptor in the mesoderm and the presence of ventral neuroblasts in the central nervous sy stem. Overproduction of ventral neuroblasts due to the forced expression of the homeodomain protein Vnd leads to increased numbers of founder cells. T hese results suggest the use of a neuroectoderm-to-mesoderm signaling pathw ay in the specification of ventral muscle precursors.