Lee, R.T., Knapik, E.W., Thiery, J.P., and Carney, T.J. (2013) An exclusively mesodermal origin of fin mesenchyme demonstrates that zebrafish trunk neural crest does not generate ectomesenchyme. Development (Cambridge, England). 140(14):2923-2932.
The neural crest is a multipotent stem cell population that arises from the dorsal aspect of the neural tube and generates
both non-ectomesenchymal (melanocytes, peripheral neurons and glia) and ectomesenchymal (skeletogenic, odontogenic, cartilaginous
and connective tissue) derivatives. In amniotes, only cranial neural crest generates both classes, with trunk neural crest
restricted to non-ectomesenchyme. By contrast, it has been suggested that anamniotes might generate derivatives of both classes
at all axial levels, with trunk neural crest generating fin osteoblasts, scale mineral-forming cells and connective tissue
cells; however, this has not been fully tested. The cause and evolutionary significance of this cranial/trunk dichotomy, and
its absence in anamniotes, are debated. Recent experiments have disputed the contribution of fish trunk neural crest to fin
osteoblasts and scale mineral-forming cells. This prompted us to test the contribution of anamniote trunk neural crest to
fin connective tissue cells. Using genetics-based lineage tracing in zebrafish, we find that these fin mesenchyme cells derive
entirely from the mesoderm and that neural crest makes no contribution. Furthermore, contrary to previous suggestions, larval
fin mesenchyme cells do not generate the skeletogenic cells of the adult fin, but persist to form fibroblasts associated with
adult fin rays. Our data demonstrate that zebrafish trunk neural crest does not generate ectomesenchymal derivatives and challenge
long-held ideas about trunk neural crest fate. These findings have important implications for the ontogeny and evolution of
the neural crest.