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. Author manuscript; available in PMC: 2019 Jun 5.
Published in final edited form as: Adv Exp Med Biol. 2017;953:209–306. doi: 10.1007/978-3-319-46095-6_6

Fig. 8.

Fig. 8

Models for Wnt/beta-catenin activation in Xenopus and zebrafish. (a) During cortical rotation in Xenopus (top) and zebrafish (bottom), beta-catenin stabilizing dorsalizing activity is transported into the equatorial region of the embryo by microtubule-mediated rotation of the cortex and through transport along microtubule arrays. Candidates for this activity include wnt11b and Lrp6/Dvl particles in Xenopus and wnt8a in zebrafish. (b) By the cleavage stages (16–128-cell stage), beta-catenin be-comes activated and enriched in dorsal vegetal and marginal nuclei until MBT. In Xenopus, priming of Wnt target genes occurs through dimethylation of Histone3 at arginine 8 (H3R8). In zebrafish, beta-catenin accumulates in dorsal marginal and dYSL nuclei, and is antagonized by multiple antagonists and calcium signaling mediators. (c) During the peri-MBT stages, beta-catenin activates direct Wnt targets and cooperates with maternal T-domain proteins (Vegt, Eomes) to activate nodal initially on the dorsal side. The combination of nodal and BMP antagonism induced by beta-catenin induce the formation of the organizer (gsc, chrd)