L. Marchant et al., THE INDUCTIVE PROPERTIES OF MESODERM SUGGEST THAT THE NEURAL CREST CELLS ARE SPECIFIED BY A BMP GRADIENT, Developmental biology (Print), 198(2), 1998, pp. 319-329
We have analyzed the role of mesoderm in the induction of the neural c
rest in Xenopus using expression of neural plate (Xsox-2) and neural c
rest (Xslug and ADAM). Conjugation experiments using different kinds o
f mesoderm together with embryonic dissection experiments suggest that
the dorsolateral mesoderm is capable of specifically inducing neural
crest cells. Neural crest markers can be induced in competent ectoderm
at varying distances from the inducing mesoderm, with dorsal tissue i
nducing neural crest at a distance while dorsolateral tissue only indu
ces neural crest directly in adjacent ectoderm. The results suggest th
at dorsal mesoderm has a high level of inducer and dorsolateral mesode
rm has a lower level, consistent with a inductive gradient. We explore
d the possible role of BMP and noggin in the generation of such a hypo
thetical gradient and found that: (1) progressively higher levels of B
MP activity are sufficient for the specification of neural plate, neur
al crest, and nonneural cells, respectively; (2) progressively higher
levels of noggin are able to induce neural crest at greater distances
from the source of inducer; and (3) modification of the levels of BMP
activity causes induction of the neural crest in absence of neural pla
te, suggesting independent induction of these two tissues. We propose
a model in which a gradient of BMP activity is established in the ecto
derm by interaction between BMP in the ectoderm and BMP inhibitors in
the mesoderm. Neural crest is induced when a threshold level of BMP is
attained in the ectoderm. The dorsolateral mesoderm produces either B
MP inhibitors or a specific neural crest inducer, with low BMP activit
y inducing neural plate while high BMP activity induces epidermis. (C)
1998 Academic Press.