File:Mesoderm development and Pax 02.jpg

Mesoderm Development and Pax

Simplified cartoon showing fates of somite regions.

• light green - sclerotome, cells in the ventromedial part of the somite de-epithelialise (Pax1 and Pax9 are expressed in a Shh-dependent manner) - axial skeleton (vertebra and intervertebral disc)
• purple - central sheet of the dermomyotome (Pax7 expressed) - integumentary dermis
• red - epaxial dermomyotome lip
• orange - epaxial myotome - muscle
• dark blue - hypaxial dermomyotome lip
• light blue - hypaxial myotome - muscle
• pink - myotomal progenitor cells.
• dark green - syndetome progenitor region - tendon

Pax gene hierarchies involved in the development of the progenitor populations of skeletal muscle, cartilage and tendon.

As the dermomyotome elongates dorsomedially and ventrolaterally, PAX3 becomes restricted to the epaxial (red) and hypaxial (dark blue) lips, where a secondary generation of myocytes delaminate and migrate to form the epaxial (orange) and hypaxial (light blue) myotome. In the limb region, PAX3+ progenitors delaminate from the hypaxial dermamyotome (light blue) and migrate into the developing limbs to provide a pool of progenitors. In these cells, PAX3 regulates the hepatocyte growth factor receptor Met, which is necessary for hypaxial delamination and migration.

Pax7 is expressed principally within the central sheet of the dermomyotome (purple); when the final somite dissociates, Pax7+ progenitors delaminate into the developing myotome. These myotomal Pax3+ Pax7+ cells (pink) retain a progenitor state in order to become a resident population necessary for skeletal muscle growth as development proceeds.

The syndetome (dark green) originates from the dorsolateral edge of the sclerotome, as Pax1 and Pax9 are downregulated and scleraxis (Scx) upregulation leads to syndegenesis. Pax, paired homeobox; MYOD1, myogenic differentiation antigen 1; MYF5, myogenic factor 5; NKX, NK homeobox; SCX, scleraxis.

(Text modified from figure legend)

Links: image - Pax and DNA | image - Pax and Mesoderm | image - somite components | PAX | somitogenesis | skeletal muscle | tendon | Axial Skeleton | Muscle | Tendon

Reference

<pubmed>24496612</pubmed>| Development

Copyright

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

Figure 4 http://dev.biologists.org/content/141/4/737/F4.expansion.html Original figure cartoon cropped, resized and relabelled. Text above modified from original figure legend.