We and others originally reported that p27 is necessary for the neuronal differentiation of embryonal carcinoma cells induced by retinoic acid and that p27 ortholog in Xenopus, Xic1, can induce the differentiation of Müller glia from retinoblasts, independently from its ability to block cell cycle progression [25, 26]. Here, CDKN1B is linked to embryonal carcinoma.