Wnt signaling in hydroid development: ectopic heads and giant buds induced by GSK-3beta inhibitors

Abstract

In Hydractinia, a colonial marine hydroid representing the basal phylum Cnidaria, Wnt signaling plays a major role in the specification of the primary body axis in embryogenesis and in the establishment of the oral pole during metamorphosis. Here we report supplementing investigations on head regeneration and bud formation in post-metamorphic development. Head and bud formation were accompanied by the expression of Wnt, frizzled and Tcf. Activation of Wnt signaling by blocking GSK-3β affected regeneration, the patterning of growing polyps and the asexual formation of new polyps in the colony. In the presence of lithium ions or paullones, gastric segments excised from adult polyps showed reversal of tissue polarity as they frequently regenerated heads at both ends. Phorbol myristate acetate, a known activator of protein kinase C increased this effect. Global activation of the Wnt pathway caused growing polyps to form ectopic tentacles and additional heads along their body column. Repeated treatment of colonies evoked the emergence of many and dramatically oversized bud fields along the circumference of the colony. These giant fields fell apart into smaller sub-fields, which gave rise to arrays of multiheaded polyps. We interpret the morphogenetic effects of blocking GSK-3β as reflecting increase in positional value in terms of positional information and activation of Wnt target genes in molecular terms.

Wnt signaling promotes oral but suppresses aboral structures in Hydractinia metamorphosis and regeneration

“…Expression pattern of Wnt3, -catenin and Tcf in normal Hydractinia polyps As previously reported (Müller et al, 2007), Hydractinia Wnt3 expression was restricted to the prospective oral poles of embryos and larvae ( Fig. 1A-C), and to the oral pole of normal polyps in both the epidermis and the gastrodermis (Fig.…”

“…Wnt3 expression also occurred at the apical pole of the gonads as previously described ( Fig. 1E) (Müller et al, 2007).…”

“…1F; Fig. 3J) (Müller et al, 2007). Throughout development, Brachyury expression was weaker than that of Wnt3 and Tcf.…”

Cnidaria

“…In the age of comparatively easy and cheap transcriptomics, future research will show what conveys such plasticity in differentiation capacity. Some fi ndings (Teo et al 2006 ;Muller et al 2007 ) point at a possible role of Wnt signaling in cell fate determination in Hydractinia .…”

“…Bipolar larvae then were shown to develop into polyps with two hypostomes . Later, more experiments confi rmed that Wnt signaling ( 2012 )) is required for the formation of the oral structures and represses the development of the aboral structures both in larvae and adults (Muller et al 2007 ;Duffy et al 2010 ). Wnt signaling is necessary for the correct development of the posterior end of the planula, which transforms into the oral end of the polyp, and the presence of the localized mRNA of Wnt signaling components at the animal end is observed as early as in the egg ).…”