Fig. 8.

Islet1 acts upstream of Hand2 in the hindlimb-field and prior to Shh activation. (A-D) Colocalization of Hand2 mRNA and ISLET1. ISLET1 immunoreactivity (A), Hand2 mRNA by in situ hybridization (B) and a merged image (C) using the same section of a hindlimb field at E9.75. (D) Higher magnification view of the LPM (boxed in C) shows nuclear signal of ISLET1 (red) and cytoplasmic Hand2 mRNA signal (green) in the same cells. (E-N) Control (E-I) and mutant (J-N) embryos at E9.75 (26-28 somite stage) and E10.0 (30/31 somite stage) were examined for gene expression. Black arrows point to normal expression, and red arrow and asterisks point to reduced and lack of expression, respectively. Hand2 expression in the mutant hindlimb field (J) is severely downregulated in comparison with controls (E). Pitx1 (F,K) and Hoxc10 (G,L) were detected in both the control (F,G) and mutant (K,L) hindlimb field. Tbx4 expression in mutants (M) was lower than that in controls (H). The characteristic expression of Hand2 in the posterior mesenchyme (I) was absent in mutant hindlimb buds at E10.0 (N).