Fig. 7. A model of WntD and Dorsal/Twist/Snail interaction in the Drosophila embryo. Dorsal and Twist cooperate to activate the expression of snail, wntD, and other genes in the ventral and lateral regions. Snail represses wntD and other neuroectodermal genes in the ventral region, thereby restricting their expression to the lateral regions and allowing ventral invagination to proceed normally. WntD in turn can negatively regulate Dorsal, probably at a step upstream of Dorsal nuclear localization.