Embryonic development of muscle patterns in the body wall of the grasshopper.

The embryonic development of the body wall musculature in the grasshopper was characterized from the appearance of the first muscle pioneers up to the establishment of a mature body wall muscle pattern. For this, a muscle-specific monoclonal antibody was used to carry out a detailed description of the temporal sequence of the developing muscle pattern in different embryonic stages. Muscle pioneers first appear at 35% of embryonic development. They form a patterned, segmentally reiterated substrate for the fusion of numerous smaller mesodermal cells. This results in the formation of an ordered array of multinuclear muscle precursor cells by the 50% stage. Subsequently, these muscle precursor cells begin to grow in size and some shift their position in the body wall. At 70% of embryonic development the pattern of muscle precursors reaches maturity, in that identified precursor cells at this stage can be related to all adult muscles. Moreover, at this stage identified muscle precursors also prefigure those muscles which will disappear during postembryonic development. Thus, between 35% and 70% of embryogenesis a basic pattern consisting of the full complement of muscle precursors is formed which is subsequently acted upon by postembryonic differentiation processes to generate the adult body wall musculature.