Cell morphogenesis and migration during zebrafish somitogenesis

Abstract

Somitic cells form the axial skeleton, dermis, and most body musculature. In zebrafish, muscle is the major somitic derivative. As muscle cells mature, they undergo a dramatic cell shape change, transforming into long myofibers that span the distance between adjacent somite boundaries. Cell elongation occurs in a medial to lateral wave in zebrafish, which correlates with and is dependent upon the migration of an early differentiating population of slow muscle fibers. Slow muscle precursors are initially the most medial muscle cells, but after somite formation they migrate laterally through the fast muscle domain and become the most superficial (lateral) muscle layer. By creating a series of genetic mosaics, we show that slow muscle cells trigger elongation of fast muscle neighbors as they pass laterally through the somite, creating a morphogenetic wave that patterns fast muscle elongation in its wake. Just one wild-type slow muscle fiber can rescue elongation of neighboring mutant cells, but not cells in adjacent somites, suggesting that a cell contact-mediated mechanism or a short-range signal relays an elongation cue from one cell to the next. Slow muscle precursors undergo a number of distinctive cell shape changes prior to the migratory event, and we are characterizing these behaviors in detail. In addition, we have identified two actin regulatory molecules expressed in slow muscle cells that are critical for slow muscle cell pre-migratory behaviors. Our current work focuses on characterizing the role of tissue-specific actin dynamics in slow muscle cell elongation and migration and on identifying the molecular nature of the slow-muscle derived elongation trigger. Research supported by NIH, March of Dimes, and a Pew Scholar Award.