DYNAMIC INTERACTIONS BETWEEN NERVE AND MUSCLE IN CAENORHABDITIS-ELEGANS

Synaptogenesis among developing motoneurons and muscles was examined i n the nematode Caenorhabditis elegans. In this animal embryonic precur sor cells give rise to regionally localized, contiguous clones of musc le cells that form two dorsal and two ventral sets that run longitudin ally along the body wall. Ablation of selected embryonic muscle precur sors resulted in gaps in the posterior dorsal muscle quadrants. We com pared the morphological development of GABAergic locomotory neurons in the presence and absence of their target muscle cells. The results le d to four main conclusions: (1) target muscle cells are not required f or the morphological differentiation of the motoneurons; (2) target mu scle cells appear to be required for the formation of presynaptic vari cosities by the motoneurons; (3) embryonic muscle cells serve as a gui de for migrating postembryonic muscle cells and in the absence of thes e guides the postembryonic muscles often assume ectopic locations; and (4) in the presence of ectopic muscle cells, the GABAergic locomotory neurons sprouted and formed branches that contributed to ectopic neur omuscular junctions. (C) 1996 Academic Press, Inc.