In wild type blastula (Control, F), wnt1 is localized to the pre-endodermal cells, visualized by the darker purple coloration. Notch is necessary to restrict wnt1 to the endoderm precursors; when it’s knocked down (Notch MASO, I), wnt1 is expressed throughout the endomesoderm. In addition, knockdown of Hox11/13b (Hox11/13b MASO, G) and Brachyury (Brachyury MASO, H) resulted in no wnt1 expression, suggesting Hox11/13b and Brachyury are also necessary for normal wnt1 mRNA expression. Note. Adapted from “Sequential Signaling Crosstalk Regulates Endomesoderm Segregation in Sea Urchin Embryos,” by A. J. Sethi et al., 2012, Science, 335, p. 590-593. Copyright 2012 by AAAS.