Fig. 1. Neural crest migration and somite development in zebrafish. Myotome is the major component of zebrafish somites. Slow muscle precursors (red), called adaxial cells, are located adjacent to notochord before segmentation (left). During segmentation stages they become a single-layered sheet of fully extended muscle cells along the anteroposterior axis and then migrate through the somite to the lateral surface (right). A subset of these cells, called muscle pioneers, remain medial and define the horizontal myoseptum (yellow). The major part of each somite is composed of fast muscle cells (orange). Sclerotome cells (blue) arise in ventromedial somite and migrate dorsally. Neural crest migrates on a medial pathway in the middle of the medial aspect of each somite (arrow).