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Fig. 3. Increased WntD expression blocks ventral invagination by interfering with
twist and snail expression. The panels in the left column,
except panel I, are wild-type embryos. The panels in the right column are
embryos expressing WntD by the nanos-Gal4-UAS system. The in situ
hybridization probes used are indicated on the left. Panels C and D are
cross-sections with dorsal side up, and all other panels are ventral views
with anterior to the left. Arrow indicates ventral furrow; arrowhead indicates
cephalic furrow. (A,B) The overall expression level of wntD was
higher in nanos-Gal4-UAS-wntD embryos than in wild-type embryos and
the expression was ubiquitous. The pictures were underexposed to show the cell
morphology. The embryo in panel B had no ventral furrow, whereas the cephalic
furrow appeared normal. (C,D) Cross-sections of gastrulating embryos showing
that no mesoderm was formed during gastrulation in embryos overexpressing
WntD. (E,F) The twist expression pattern was much reduced in embryos
overexpressing WntD. In wild-type embryos, twist expression is
approximately 22 cells wide along the dorsoventral axis at the onset of
gastrulation. The embryo shown in E already had some of the cells invaginated.
(G) A wild-type embryo showing the normal snail pattern. (H-J) The
panels show the reduced snail pattern with increasing severity in
embryos overexpressing WntD. Some embryos showed narrower patterns of
expression whereas others showed no expression in the anterior regions. (K-N)
WntD overexpression also causes sim and rhomboid to show
abnormal expression patterns. In wild-type embryos, the expression of
sim and rhomboid in the ventral cells is repressed by Snail.
Moreover, the positioning of sim also requires Snail. Thus, the
abnormal patterns of sim and rhomboid in panels L and N
correlate well with the reduced snail pattern.
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