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. Hierarchical
clustering based on the 48 hpf PrImR data (Figure 6M)
supports this distinction: one cluster comprised the flaskshaped
sensory-neurosecretory cells and the adjacent serotoninergic
cell, which, in addition to the absence of six3
and presence of otp, miR-7 and phc2 (see above), expressed
carboxypeptidase-E (cpe) and other genes not directly
linked to neurosecretion, such as smad2/3. This cluster
corresponded to the otp + cells devoid of six3 expression at
24 hpf (see above). Another well-supported cluster