File:Somite patterning.jpg

Somite patterning and fate.

Somite development involves two patterning systems operating along the A-P and D-V axes. (i) Unsegmented presomite mesoderm and nascent somites showing the oscillations and gradients of gene activity that determine A-P polarity prior to overt somite formation (green: anterior half-somite; red: posterior half-somite). (ii) Transverse section through an A-half-epithelial somite (esm, left) and a differentiated somite (right). Patterning along the D-V axis sub-divides the somite into dermatome (dr), myotome (m) and sclerotome (s). The sclerotome is further sub-divided into ventral (v), central (s, red) and (d) dorsal regions. (iii) Representation of two somites viewed laterally, showing the central sclerotome A-P sub-division. Only the anterior-half (green) is permissive for PNS components. (iv) In differentiated vertebrae, posterior-central sclerotomes form the paired transverse processes and pedicles of the neural arches (red) that encase the spinal cord and provide attachment points for epaxial muscles. Anterior central-sclerotome derivatives (green) contribute to peripheral nerve sheaths and prefigure the positions of the intervertebral foraminae (ivf). Spinous process (sp), intervertebral disc (ivd), vertebral body (vb).

Original Image name: 1471-213X-9-30-1.jpg

Hughes et al. BMC Developmental Biology 2009 9:30 doi:10.1186/1471-213X-9-30 The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1471-213X/9/30

1471-213X-9-30-1.jpg

© 2009 Hughes et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.