Segmentation in vertebrates: clock and gradient finally joined.
The vertebral column is derived from somites formed by segmentation of presomitic mesoderm, a fundamental process of vertebrate embryogenesis. Models on the mechanism controlling this process date back some three to four decades. Access to understanding the molecular control of somitogenesis has been gained only recently by the discovery of molecular oscillators (segmentation clock) and gradients of signaling molecules, as predicted by early models. The Notch signaling pathway is linked to the oscillator and plays a decisive role in inter- and intrasomitic boundary formation. An Fgf8 signaling gradient is involved in somite size control. And the (canonical) Wnt signaling pathway, driven by Wnt3a, appears to integrate clock and gradient in a global mechanism controlling the segmentation process. In this review, we discuss recent advances in understanding the molecular mechanism controlling somitogenesis.
Aulehla
Alexander
A
Max-Planck-Institute for Molecular Genetics, Department of Developmental Genetics, 14195 Berlin, Germany.
Herrmann
Bernhard G
BG
D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D019521:Body Patterning / Q000502:physiology*; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051880:Receptors, Notch; D015398:Signal Transduction / Q000502:physiology; D019170:Somites / Q000502:physiology*; D014714:Vertebrates / Q000196:embryology*; D051153:Wnt Proteins
D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D051880:Receptors, Notch; D051153:Wnt Proteins; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors