From apolar gastrula to polarized larva: Embryonic development of a marine hydroid, Dynamena pumila. Issue 5 (1st December 2021) - Vetrova, Alexandra A.
Abstract: Background: In almost all metazoans examined to this respect, the axial patterning system based on canonical Wnt (cWnt) signaling operates throughout the course of development. In most metazoans, gastrulation is polar, and embryos develop morphological landmarks of axial polarity, such as blastopore under control/regulation from cWnt signaling. However, in many cnidarian species, gastrulation is morphologically apolar. The question remains whether сWnt signaling providing the establishment of a body axis controls morphogenetic processes involved in apolar gastrulation. Results: In this study, we focused on the embryonic development of Dynamena pumila, a cnidarian species with apolar gastrulation. We thoroughly described cell behavior, proliferation, and ultrastructure and examined axial patterning in the embryos of this species. We revealed that the first signs of morphological polarity appear only after the end of gastrulation, while molecular prepatterning of the embryo does exist during gastrulation. We have shown experimentally that in D. pumila, the direction of the oral‐aboral axis is highly robust against perturbations in cWnt activity. Conclusions: Our results suggest that morphogenetic processes are uncoupled from molecular axial patterning during gastrulation in D. pumila . Investigation of D. pumila might significantly expand our understanding of the ways in which morphological polarization and axial molecular patterning are linked in Metazoa. Key Findings: Embryonic development of a non‐model hydrozoan D. pumila was thoroughly described. D. pumila gastrulates in an apolar fashion via a combination of primary and secondary delamination. Morphological polarity appears after the end of gastrulation, but molecular prepatterning exists during gastrulation. Morphogenetic processes are uncoupled from cWnt‐mediated molecular polarity during gastrulation The direction of the primary body axis is highly robust against perturbations in cWnt activity in D. pumila .