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 thora cic and abdominal segments of the grasshopper Schistocerca gregaria at the identified cell level. We visualized differentiating muscle pione er and muscle precursor cells by staining with a muscle-specific monoc lonal antibody and with rhodamine-coupled phalloidin. Our results show that a similar pattern of serially reiterated early muscle pioneers i s initially established in all segments. Subsequently, two major segme ntal differentiation processes occur. First, segment-specific sets of additional, later differentiating muscle pioneers are generated de nov o. Second, segment-specific sets of existing early muscle precursors a re eliminated through atrophy and eventual loss. These events have con sequences for matching homonomy of muscles and their innervating moton eurons. 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.