Special Issue Reviews–A Peer Reviewed Forum
The genetics and embryology of zebrafish metamerism
Version of Record online: 7 MAY 2007
Copyright © 2007 Wiley-Liss, Inc.
Special Issue: Special Focus on Segmentation
Volume 236, Issue 6, pages 1422–1449, June 2007
How to Cite
Holley, S. A. (2007), The genetics and embryology of zebrafish metamerism. Dev. Dyn., 236: 1422–1449. doi: 10.1002/dvdy.21162
- Issue online: 16 MAY 2007
- Version of Record online: 7 MAY 2007
- Manuscript Accepted: 22 MAR 2007
- NICHD. Grant Number: R01 HD045738
- American Cancer Society. Grant Number: RSG-07-05001-DDC
- somite morphogenesis;
- myotome, sclerotome
Somites are the most obvious metameric structures in the vertebrate embryo. They are mesodermal segments that form in bilateral pairs flanking the notochord and are created sequentially in an anterior to posterior sequence concomitant with the posterior growth of the trunk and tail. Zebrafish somitogenesis is regulated by a clock that causes cells in the presomitic mesoderm (PSM) to undergo cyclical activation and repression of several notch pathway genes. Coordinated oscillation among neighboring cells manifests as stripes of gene expression that pass through the cells of the PSM in a posterior to anterior direction. As axial growth continually adds new cells to the posterior tail bud, cells of the PSM become relatively less posterior. This gradual assumption of a more anterior position occurs over developmental time and constitutes part of a maturation process that governs morphological segmentation in conjunction with the clock. Segment morphogenesis involves a mesenchymal to epithelial transition as prospective border cells at the anterior end of the mesenchymal PSM adopt a polarized, columnar morphology and surround a mesenchymal core of cells. The segmental pattern influences the development of the somite derivatives such as the myotome, and the myotome reciprocates to affect the formation of segment boundaries. While somites appear to be serially homologous, there may be variation in the segmentation mechanism along the body axis. Moreover, whereas the genetic architecture of the zebrafish, mouse, and chick segmentation clocks shares many common elements, there is evidence that the gene networks have undergone independent modification during evolution. Developmental Dynamics 236:1422–1449, 2007. © 2007 Wiley-Liss, Inc.