An organizing region in metamorphosing hydrozoan planula larvae - stimulation of axis formation in both larval and in adult tissue

Abstract

A novel wingless gene was isolated from the marine colonial hydroid Hydractinia echinata. Alignments and Bayesian inference analysis clearly assign the gene to the Wnt5A group. In line with data found for the brachyury ortholog of Hydractinia, He-wnt5A is expressed during metamorphosis in the posterior tip of the spindle-shaped planula larva, suggesting that the tip functions as a putative organizer during metamorphosis. Additionally, the outermost cells of the posterior tip are omitted from apoptosis during metamorphosis. In order to investigate this putative organizer function, we transplanted the posterior tip of metamorphosing animals into non-induced larvae and into primary polyps 24 h and 48 h of age. In larvae, the tip induced formation of a secondary axis. In polyps the building of ectopic head structures was induced. Based on our data on axis formation, on gene expression similar to the organizers of other species, and the absence of regular apoptosis, we conclude that the posterior tip of the Hydractinia larva has organizing activity during metamorphosis.

Lineage‐specific evolution of cnidarian Wnt ligands

“…The genes were Wnt1, Wnt2, Wnt5b, Wnt7, Wnt8, Wnt9/10, Wnt11a, Wnt11b , and Wnt16 . Together with the two previously published Wnt3 and Wnt5a of H. echinata (Plickert et al ; Duffy et al ; Stumpf et al ), this resulted in a total of 11 Wnt ligands in H. echinata .…”

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

“…Brachyury (Duffy et al, 2010;Stumpf et al, 2010) and Nanos are also expressed at this pole in Hydractinia embryos and in Podocoryne and Nematostella larvae (Torras et al, 2004(Torras et al, , 2005Extavour et al, 2005). Thus, if Nanos is chosen as point of reference, the posterior pole of the larva and, hence, the oral pole of the polyp, correspond to the posterior pole in Drosophila.…”

The embryonic development of the cnidarian Hydractinia echinata

“…Despite gastrulating in an apolar fashion, the embryo is strictly polarized: maternal transcripts of canonical Wnt signaling are asymmetrically deposited in the oocyte and govern the establishment of the primary body axis (Plickert et al ). Transplantation experiments have shown that the posterior (prospective oral) pole of the planula has organizer capabilities (Stumpf et al ).…”