Control of muscle fibre and motoneuron diversification

Recent studies have elucidated both the mechanism of early formation of div erse muscle fibre types and the matching of diverse populations of motoneur ons to their appropriate muscle targets. Highlights include the demonstrati on that distinct signals are necessary for the formation of several distinc t myoblast populations in the vertebrate somite, the identification of moto neuron subtypes, studies of how motoneurons target appropriate muscles, and rapid progress on the Drosophila neuromuscular system. We propose a model in which four classes of decision control the patterning of both motoneuron s and muscles.