Regulation of muscle growth and sarcomeric protein gene expression over the intermolt cycle

Crustacean muscle growth is associated with a hormonally mediated cyclical molt stage, The mechanisms by which fibre lengthening and hypertrophy occur in Crustaceans over the molt has been the subject of our and other researc hers' investigations using histological, biochemical and molecular approach es, In this paper, we review our studies and present evidence for the diffe rent molecular mechanisms by which sarcomeric proteins are upregulated to a chieve muscle sarcomere addition in lobsters during the molt. Synthesis of the sarcomeric proteins has been shown to increase during the premolt and postmolt phases in the leg and abdominal muscles coinciding wit h the addition of sarcomeres over ecdysis. This is in contrast to research on claw muscle demonstrating premolt atrophy. Our work and others' have inv estigated the factors which modulate this growth and turnover of muscle tis sue in crustaceans. These changes in muscle turnover correspond with an ele vated titre of circulating ecdysteroids and the role of these molting hormo nes in regulating sarcomeric mRNA and protein levels during cyclical muscle growth is discussed. Our results suggest that sarcomeric proteins may be controlled via both tra nscriptional and translational mechanisms during the molt interval and thes e findings are discussed in relation to previous research investigating mus cle growth in Crustacea.