Differential effects of N-cadherin-mediated adhesion on the development of myotomal waves

Abstract

Myotomal fibers form by a first wave of pioneer myoblasts from the medial epithelial somite, and by a second wave from all four lips of the dermomyotome. Then, a third wave of mitotic progenitors colonizes the myotome, initially stemming from the extreme lips and, later, from the central dermomyotome sheet. In vitro studies have suggested that N-cadherin plays a role in myogenesis, but its role in vivo remains poorly understood. We find that during the growth phase of the dermomyotome sheet, when the orientation of mitotic spindles is parallel to the mediolateral extent of the epithelium, N-cadherin protein is inherited by both daughter cells. Prior to dermomyotome dissociation into dermis and muscle progenitors, when mitoses become perpendicularly oriented, N-cadherin remains associated only with the apical cell located in apposition to the myotome, generating molecular asymmetry between basal and apical progeny. Local gene missexpression confirms that N-cadherin-mediated adhesion is sufficient to promote myotome colonization, whereas its absence drives cells towards the subectodermal domain, hence coupling the asymmetric distribution of N-cadherin to a shift in mitotic orientation and to fate segregation. Site-directed electroporation to additional, discrete somite regions, further reveals that N-cadherin-mediated adhesion is necessary for maintaining the epithelial configuration of all dermomyotome domains while promoting the onset of Myod transcription and the translocation into the myotome of myofibers and/or of Pax-positive progenitors. By contrast, N-cadherin has no effect on migration or differentiation of the first wave of myotomal pioneers. Altogether, we show for the first time that the asymmetric localization of N-cadherin during mitosis indirectly influences fate segregation by differentially driving the allocation of progenitors to muscle versus dermal primordia, that the adhesive domain of N-cadherin maintains the integrity of the dermomyotome epithelium, which is necessary for myogenic specification, and that different molecular mechanisms underlie the establishment of pioneer and later myotomal waves.

Antagonistic roles of full-length N-cadherin and its soluble BMP cleavage product in neural crest delamination

“…and C.K., unpublished). Consistent with these results, both cN390⌬-GFP and CBR-GFP have been shown to cause an initial loss of epithelial morphology in cells of the avian dermomyotome, yet they had opposite effects in driving cell segregation into dermal or myotomal domains, respectively (Cinnamon et al, 2006). These constructs also altered the morphology of epithelial cell lines (Fujimori and Takeichi, 1993), but, surprisingly, when misexpressed using an adenoviral approach, they had no effect on NT morphology (Nakagawa and Takeichi, 1998).…”

The transition from differentiation to growth during dermomyotome-derived myogenesis depends on temporally restricted hedgehog signaling

“…In the DM, one possible event that coincides in time with loss of Shh responsiveness is its conversion into mesenchyme, during which production of myotomal fibers is substituted by mitotic Pax7 + progenitors that are Shh-insensitive in both mice and avians. DM dissociation is triggered by myotomal fibroblast growth factor signaling (Delfini et al, 2009), and by loss of N-cadherin (cadherin 2), which also alters their apicobasal polarity (Ben-Yair et al, 2011;Cinnamon et al, 2006); the processes described above could alter the composition or organization of cilia responsible for signal transduction (Eggenschwiler and Anderson, 2007). Along this line, apically aligned cilia present in the epithelial DM change their distribution upon DM dissociation to become randomly localized on the cell surface (our unpublished data).…”

“…Studies in avians showed that around embryonic day (E) 2.5 the lips generate myocytes (Cinnamon et al, 2006;Cinnamon et al, 1999;Gros et al, 2004;Huang and Christ, 2000;Kahane et al, 1998b;Kahane et al, 2002) that intercalate among a scaffold of earlier pioneer fibers and depend on integrity of this scaffold for proper patterning (Kahane et al, 1998a;Kahane et al, 2007). Similarly, progenitors delaminate from the central DM sheet and generate differentiated myocytes (Ben-Yair et al, 2011).…”

N-cadherin ligation, but not Sonic hedgehog binding, initiates Cdo-dependent p38α/β MAPK signaling in skeletal myoblasts

“…The Cdo ectodomain does not interact with itself in trans and has no obvious adhesive properties, but it binds several proteins as a putative coreceptor (9,(11)(12)(13)(14). In myoblasts, Cdo forms cis complexes with the cell-cell adhesion molecule N-cadherin (Ncad) (11), which is itself promyogenic (15)(16)(17)(18)(19)(20). Cell-cell contact stimulates myoblast differentiation, and although Ncad is not essential for myogenesis (likely due to redundancy with other cadherins) (21), direct Ncad ligation can substitute for cell-cell contact to enhance muscle-specific gene expression and myoblast differentiation (17,19).…”