Segmental differentiation processes in embryonic muscle development of the grasshopper.

To analyse segmental differentiation processes in muscle development, we studied the embryogenesis of the ventral body wall muscles in thoracic and abdominal segments of the grasshopper Schistocerca gregaria at the identified cell level. We visualized differentiating muscle pioneer and muscle precursor cells by staining with a muscle-specific monoclonal antibody and with rhodamine-coupled phalloidin. Our results show that a similar pattern of serially reiterated early muscle pioneers is initially established in all segments. Subsequently, two major segmental differentiation processes occur. First, segment-specific sets of additional, later differentiating muscle pioneers are generated de novo. Second, segment-specific sets of existing early muscle precursors are eliminated through atrophy and eventual loss. These events have consequences for matching homonomy of muscles and their innervating motoneurons. Taken together, these processes in the embryo, in concert with postembryonic differentiation events, play critical roles in shaping the highly specialized muscular structures of the mature animal.