azakenpaullone, a selective inhibitor of Gsk3β [49] that
has been shown to trigger nuclear β-catenin accumulation
in Platynereis, mimicking ectopic activation of Wnt signaling
[47,50]. We found that azakenpaullone specifically
knocked down or abolished apical expression of episphere
markers, including the broadly expressed six3 (Figure 5A)
and foxq2 (Figure 5B) in a concentration-dependent manner,
with the majority of expression reduced or lost between
1 μM and 5 μM (Figure 5). Conversely, the
expression of pax6, which occupies a more ventral peripheral
position in the larval episphere [51] (overlapping with
Wnt4; Figure 4E), was expanded at 0.5 μM to 10 μM
concentrations of azakenpaullone (Figure 5E). The number
of otp + apical organ cells was also reduced at higher
concentrations of azakenpaullone (Figure 5C), with all
cells absent at 5 and 10 μM concentrations. By contrast,
the expression of hox1 in the apical tuft cells persisted
at all concentrations (Figure 5D, arrows). This may
have been because tuft cells are among the first cells
to differentiate in the apical plate (Figure 6A). To
test the dynamic role of Wnt signaling in episphere
patterning, we conducted washout experiments in