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Resegmentation of Somites

Resegmentation of somites to form sclerotomes and changes of sclerotomal primordia to mature vertebral parts. The somitic and primordial origins of vertebral parts and phenotypic parts are colour-matched, and the locations of the somites, resegmented sclerotomes, and vertebrae along the embryonic axis are approximately counter-registered.

During resegmentation, the sclerotome is formed from the caudal and rostral halves of two adjacent somites, such that the middle of the resegmented sclerotome lines up with the intersomitic cleft (IC). Both the axial sclerotome (Scl-A) and lateral sclerotome (Scl-L) develop dense and loose zones. The dense zone of the lateral sclerotome (Ld) becomes the neural arch (NA) and pedicle (P), which is attached to the rostral part of the vertebral body (VB) formed from chondrification of the loose (Al) and part of the dense zones (Ad) of the axial sclerotome. The rostral layer of the dense zone of the axial sclerotome soon forms the intervertebral boundary zone (IBZ) containing intervertebral boundary mesenchyme (IBM), which ultimately forms the annulus (A) and, together with notochord remnants (NC), the nucleus pulposus (NP) of the intervertebral disc (ID). The loose zone of the lateral sclerotome (Ll) does not form bone but promotes emergence of the nerve roots (NR).

The neural arch is derived from a single somite but the vertebral body receives contributions from two adjacent somites. IV intersomitic vessel. Arrows indicate developmental fates of the sclerotomes.

Links: Axial Skeleton

Reference

<pubmed>21193993</pubmed>| PMC3055990 | Childs Nerv Syst.

Copyright

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