An Early Role for Wnt Signaling in Specifying Neural Patterns of Cdx and Hox Gene Expression and Motor Neuron Subtype Identity
Figure 10
Hox Gene Profiles Induced by Wnt, RA, and/or FGF Signals Predict Later MN Subtype
(A) Schematic drawing of a stage 4 embryo. Dotted line indicates the presumptive neural plate. Red box indicates prospective FB explants used for in vitro studies.
(B–E) Explants were cultured alone or exposed to Wnt, RA, and/or FGF4 for 44 h, then washed and exposed to Shh-N (15 nM) for an additional 22 h. Bars represent mean ± s.e.m. number of Tbx20+ /Isl+, Hb9+/Isl+, and Hb9+/Hoxc9+ cells, respectively, as percentage of total cell number.
(B–E) Each row represents consecutive sections from a single explant.
(B) Stage 4 FB explants cultured alone, before exposure of Shh-N, generated Isl+ cells but no Tbx20+, Hb9+, or Hoxc9+ cells ( n = 6 explants).
(C) Stage 4 FB explants cultured in the presence of Wnt3A (̃150 ng/ml) and RA (10 nM), before exposure of Shh-N, generated Tbx20+ /Isl+ cells but no, or very few, Hb9+/Isl+ cells and no Hoxc9+ cells ( n = 12 explants).
(D) Cultivation in the presence of Wnt3A (̃150 ng/ml), RA (10 nM), and FGF4 (30 ng/ml), before exposure of Shh-N, generated Hb9+/Isl+ cells and only a few Tbx20+/Isl+ and Hb9+/Hoxc9+ cells ( n = 14 explants).
(E) Cultivation in the presence of Wnt3A (̃150 ng/ml) and FGF4 (60 ng/ml), before exposure of Shh-N, generated Hb9+/Isl+ and Hb9+/Hoxc9+ cells but no Tbx20+ cells ( n = 9 explants). Scale bars represent 100 μm (Isl) and 50 μm (double labels), respectively.