Practice question

Early after fertilization vegetal cortical region contains Wnt11 mRNA and Dishevelled protein anchored to cortex. Microtubule polymerization between sperm aster and vegetal cortex enables plus-end directed transport of these determinants via kinesin toward future dorsal side during 30-degree cortical rotation. Imaging with Dsh-GFP demonstrates accumulation in dorsal marginal zone preceding beta-catenin nuclear entry. Translocation to ventral side would induce ectopic axis, to animal hemisphere or vegetal pole alone insufficient. Normal pattern to dorsal side establishes Nieuwkoop center and dorso-ventral polarity. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.