Fig. 12
Schematic representation of Pdu-Tcf expression and the role of Wnt/β-catenin signalling in gut development. This diagram summarizes the expression of Pdu-Tcf from the 72 hpf stage with putative gut primordium, through 5 dpf stage with uncellularized gut to 7 dpf larva with a functional, compartmentalized digestive tract. Midgut marker genes are generally downregulated by inhibition of Wnt/β-catenin signalling, whereas hindgut marker gene Pdu-Legumain expands to midgut. The expression profile of these genes in midgut is thus more reminiscent of the hindgut upon Wnt inhibition. On the other hand, another hindgut gene Cdx is slightly downregulated upon inhibition. We did not observe any pronounce effect of Wnt/β-catenin pathway activation, except for Cdx which is upregulated in the midgut. The expression of the endodermal marker, Nk2.1, which is present in both compartments under normal circumstances, is not changed by either manipulations of the Wnt/β-catenin pathway. According to our scenario, Wnt/β-catenin signalling is necessary for endoderm to differentiate into midgut secretory epithelium and its inhibition causes midgut cells to be functionally converted to the hindgut