Fig. 2

hand2 inhibits IM production.

(A–C) Dorsal views, anterior to the left, of the posterior mesoderm at the 11 somite stage. In situ hybridization depicts normal expression of pax2a in the IM (arrows) of wild-type embryos (A), widened expression in han^s6 mutants (B), and lack of expression in hand2-overexpressing embryos (hs:hand2) (C). Expression in the spinal neurons (asterisk) is unaffected by altered hand2 function. Scale bar represents 100 μm. (D–F) Pax2a immunofluorescence in the posterior mesoderm of wild-type (D), han^s6 mutant (E), and hs:hand2 (F) embryos at the 12 somite stage. Dorsal views, anterior to the left, are three-dimensional reconstructions of flat-mounted embryos from which the yolk and anterior tissues have been dissected away. Scale bar represents 100 μm. (D'–F') Magnification of 250 µm long regions from (D–F) used for quantification of the number of Pax2a⁺ cells in wild-type (D'), han^s6 mutant (E'), and hs:hand2 (F') embryos. White dots indicate Pax2a⁺ nuclei. Intensity of staining varied from strong (for example, green arrows) to weak (for example, yellow arrows). Scale bar represents 25 μm. (G) Bar graph indicates the average number of Pax2a⁺ cells per 100 µm of IM in wild-type, han^s6, and hs:hand2 mutant embryos; error bars indicate standard deviation. Asterisks indicate a statistically significant difference compared to wild-type (p<0.0001, Student’s t test; n=13 for wild-type, n=10 for han^s6, and n=19 for hs:hand2).