Genetic interaction between SoxC and Ctnnb1. (A–D) External and histological aspect of hind paws from E14.5 SoxC/Ctnnb1/Prx1CreER control, partial, and compound mutant embryos. (A) The Sox4^fl/fl11^fl/fl12^−/−Prx1CreER paw displays anterior–posterior (red arrow) fusions of cartilage primordia. (B) The Ctnnb1^fl/flPrx1CreER paw is tiny and malformed and has a large hematoma (H). (C) The Ctnnb1^fl/+Prx1CreER paw is normal. (D) Most Sox4^fl/+11^fl/fl12^+/−Prx1CreER paws are normal (left), but some develop soft-tissue syndactyly of digits 3 and 4 (red arrow, right). Most Sox4^fl/+11^fl/fl12^+/−Ctnnb1^fl/+Prx1CreER paws show soft-tissue fusions without (left) or with (right) cartilage fusions. Also see Table S1. (E and F) SOX9 immunostaining (red) in sections adjacent to those in A–D. Top images are composites of more than one original image. Bottom images are magnified pictures of boxed regions from a single image. They show SOX9 continued expression between digits 3 and 4 in SoxC^Prx1CreER (E) and SoxC/Ctnnb1^Prx1CreER limbs (F). Data were reproduced in at least three experiments. Each panel shows representative results.