All Xenopus laevis experiments reported in this study were approved by the Lund/Malmö regional ethical committee (M140-14). The embryos were prepared, cultured and analyzed by Red-Gal staining, whole-mount in situ hybridization and TUNEL assay as described previously (Pera et al., 2015). For histological staining, embryos were fixed in Bouin's solution, dehydrated, embedded in paraffin, sectioned at 10 μm, dewaxed and stained with hematoxylin and eosin. For cartilage staining, tadpoles were fixed in MEMFA (0.1 M MOPS, 2 mM EGTA, 1 mM MgSO4, 3.7% formaldehyde, pH 7.4), dehydrated, and stained in Alcian Blue solution; the facial skeleton was dissected after rehydration in 80% glycerol in 2% KOH.
