In line with our observation that at 24 hpf the apical
organ region including the tuft cells was devoid of six3
expression, the tuft cells themselves and the directly
ventrally adjacent sensory-neurosecretory and serotoninergic
cells were six3-negative at 48 hpf. By contrast, the
crescent and mechanoreceptor cells expressed six3 and
thus, by molecular identity, appear to represent differentiated
cell types of the surrounding apical plate.