Wnt signaling in hydroid development: Formation of the primary body axis in embryogenesis and its subsequent patterning

Abstract

We have studied the role the canonical Wnt pathway plays in hydroid pattern formation during embryonic development and metamorphosis. Transcripts of Wnt and Tcf were asymmetrically deposited in the oocyte and subsequent developmental stages, marking the sites of first cleavage, posterior larval pole and the upcoming head of the metamorphosed polyp. To address the function of these genes, we activated downstream events of the Wnt pathway by pharmacologically blocking GSK-3beta. These treatments rendered the polar expression of Tcf ubiquitous and induced development of ectopic axes that contained head structures. These results allow concluding that Wnt signaling controls axis formation and regional tissue fates along it, determining one single axis terminus from which later the mouth and hypostome develop. Our data also indicate Wnt functions in axis formation and axial patterning as in higher metazoans, and thus point to an ancestral role of Wnt signaling in these processes in animal evolution.

Hydractinia, a pioneering model for stem cell biology and reprogramming somatic cells to pluripotency

“…in the terminal region of the developing larva tail (Fig. 4), and its derivative, the oral pole of the polyp Plickert et al, 2006;Duffy et al, 2010). This is explained in more detail in the following section.…”

The Wnt code: cnidarians signal the way

“…An analysis of the function of gsk-3b during gametogenesis indicates that an inhibition of Wnt signalling is crucial for oogenesis (Rentzsch et al, 2005). Transcripts of fzd, b-cat, and tcf are maternally supplied and persist throughout embryogenesis (Frobius et al, 2003), while wnt transcripts appear at the onset of gastrulation in Nematostella and other cnidarians (Kusserow et al, 2005;Lee et al, 2006;Plickert et al, 2006). However, it remains unclear whether one of the wnt genes is involved the early steps of embryogenesis.…”

“…Also data from Hydractinia echinata, a colonial marine hydrozoan species, support the function of Wnt signalling in axial patterning. Inhibition of GSK-3b activity with alsterpaullone causes ectopic axes in embryos and the formation of ectopic tentacles in adult polyps of the colony (Muller et al, 2004a, b;Plickert et al, 2006;Teo et al, 2006). In Hydractinia, Wnt/b-catenin signalling , while the Wnt-anatagonist hydkk1/2/4 is expressed in the body column (Guder et al, 2006).…”

Modeling pattern formation in hydra: a route to understanding essential steps in development

“…Essential for their axial organization is the Wnt pathway Broun et al, 2005;Kusserow et al, 2005;Bosch 2007; Lengfeld et al, 2009;Plickert et al, 2006;Gee et al, 2010;Duffy et al, 2010). A comparison of the expression patterns of Wnt, Brachyury and several other genes in hydra and higher organisms suggests that the head of the hydra, in contrast to its usual naming, represents the most posterior and the foot the most anterior structure (Meinhardt, 2002).…”