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.