We have inhibited normal cell-cell interactions between mesoderm and ectoderm in wild-type Drosophila embryos, and have assayed the consequences on muscle development. Although most cells in gastrulation-arrested embryos do not differentiate, they express latent germ layer-specific genes appropriate for their position. Mesoderm cells require proximity to ectoderm to express several muscle-specific genes. We show that ventral ectoderm induces mesoderm cells to express nautilus (a MyoD homologue)

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... and to differentiate somatic myofibers, whereas dorsal ectoderm induces mesoderm cells to express visceral and cardiac muscle-specific genes. Our findings suggest that muscle determination in Drosophila is regulated by induction between germ layers during gastrulation.