Figure 1A. Copyright: Reprinted with permission from Elsevier from [doi:10.1016/S0925-4773(99)00016-7] Mech Dev 82: 205-11, de Roos K; Sonneveld E; Compaan B; ten Berge D; Durston AJ; van der Saag PT, Expression of retinoic acid 4-hydroxylase (CYP26) during mouse and Xenopus laevis embryogenesis. Copyright 1999.