Abstract
Formation of the vertebrate postcranial body axis follows two sequential but distinct phases. The first phase generates pre-sacral structures (the so-called primary body) through the activity of the primitive streak on axial progenitors within the epiblast. The embryo then switches to generate the secondary body (post-sacral structures), which depends on axial progenitors in the tail bud. Here we show that the mammalian tail bud is generated through an independent functional developmental module, concurrent but functionally different from that generating the primary body. This module is triggered by convergent Tgfbr1 and Snai1 activities that promote an incomplete epithelial to mesenchymal transition on a subset of epiblast axial progenitors. This EMT is functionally different from that coordinated by the primitive streak, as it does not lead to mesodermal differentiation but brings axial progenitors into a transitory state, keeping their progenitor activity to drive further axial body extension.
Highlights
Formation of the vertebrate body is a complex and dynamic process involving a series of sequential growth and patterning activities
At the end of gastrulation, during the socalled primary body formation axial progenitors are located in the epiblast, an epithelial layer at the caudal embryonic end, and their activity is organized by the primitive streak (PS) (Aires et al, 2018; Holmdahl, 1925; Steventon and Martinez Arias, 2017)
These results suggest that progress into tail bud stages requires that axial progenitors undergo an epithelial to mesenchymal transition (EMT)
Summary
Formation of the vertebrate body is a complex and dynamic process involving a series of sequential growth and patterning activities. At the end of gastrulation, during the socalled primary body formation (i.e. post-occipital region of the head, neck and trunk) axial progenitors are located in the epiblast, an epithelial layer at the caudal embryonic end, and their activity is organized by the primitive streak (PS) (Aires et al, 2018; Holmdahl, 1925; Steventon and Martinez Arias, 2017). At this stage, the embryo contains axial progenitors with different potencies. Axial progenitors, which are restricted to NMPs, are located in the tail bud (Benazeraf and Pourquie, 2013; Henrique et al, 2015; Steventon and Martinez Arias, 2017; Wilson et al, 2009)
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