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Fig. 1. Neuronal cell fate specification and guidance of commissural axons by
morphogens and Netrin 1. Three sets of morphogens, Shh, BMPs and Wnts, are
first used to pattern neural progenitors in the spinal cord, and then appear
to be reused as guidance cues for commissural axons. (A) In the early neural
tube, Shh, BMP and Wnt protein concentration gradients act to specify neural
cell fate in the ventral and dorsal spinal cord. (B) Later, the axons of
differentiated commissural neurons are repelled from the dorsal midline by
BMPs (red) and attracted to the ventral midline by the combined
chemoattractant effects of Netrin 1 and Shh (blue). (C,D) After crossing the
floor plate, commissural axons are attracted anteriorly by a Wnt4 gradient (C,
green) and repelled from the posterior pole by a Shh gradient (D, orange). A
and B, and left panels in C and D, are cross section representations of the
developing spinal cord; right panels in C and D are open book representations.
V0-3, ventral interneuron sub-populations; dI1-6, dorsal interneuron
sub-populations; MN, motoneurons; RP, roof plate; FP, floor plate; D, dorsal;
V, ventral; P, posterior; A, anterior.
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