Fig. 6. p27^Xic1 is required for muscle differentiation. Western blot for endogenous p27^Xic1 protein in uninjected embryos and embryos injected with 20 ng Con Mo or 20 ng p27^Xic1 Mo harvested at stage 22. Cytoskeletal ß-tubulin is used as a loading control. Embryos were injected with 20 ng p27^Xic1 Mo (B-D,F,H,K), 20 ng Con Mo (E,J) or 20 ng p27^Xic1 Mo + 20 pg p21^Cip1 (G) along with ß-gal (light blue, injected side towards the left) and analyzed at stage 15 for expression of MyoD (B), Myf5 (C), MA (E) and MHC (E-G) by whole-mount in situ hybridization. Embryos injected with 20 ng p27^Xic1 Mo were incubated in HUA from gastrulation until stage 22 and analyzed by whole-mount antibody staining for 12/101 expression (H,I). Embryos injected with 20 ng Con Mo (J) or p27^Xic1 Mo (K) were analyzed for apoptotic cells at stage 15 by whole-mount TUNEL staining.