Early development and axis specification in the sea anemone Nematostella vectensis

Abstract

We investigated the early development of the sea anemone Nematostella vectensis, an emerging model system of the Cnidaria. Early cleavage stages are characterized by substantial variability from embryo to embryo, yet invariably lead to the formation of a coeloblastula. The coeloblastula undergoes a series of unusual broad invaginations-evaginations which can be blocked by cell cycle inhibitors suggesting a causal link of the invagination cycles to the synchronized cell divisions. Blastula invagination cycles stop as cell divisions become asynchronous. Marking experiments show a clear correspondence of the animal-vegetal axis of the egg to the oral-aboral axis of the embryo. The animal pole gives rise to the concave side of the blastula and later to the blastopore of the gastrula, and hence the oral pole of the future polyp. Asymmetric distribution of granules in the unfertilized egg suggest an animal-vegetal asymmetry in the egg in addition to the localized position of the pronucleus. To determine whether this asymmetry reflects asymmetrically distributed determinants along the animal-vegetal axis, we carried out blastomere isolations and embryonic divisions at various stages. Our data strongly indicate that normal primary polyps develop only if cellular material from the animal hemisphere is included, whereas the vegetal hemisphere alone is incapable to differentiate an oral pole. Molecular marker analysis suggests that also the correct patterning of the aboral pole depends on signals from the oral half. This suggests that in Nematostella embryos the animal hemisphere contains organizing activity to form a normal polyp.

Nervous systems of the sea anemone Nematostella vectensis are generated by ectoderm and endoderm and shaped by distinct mechanisms

“…Oral halves develop into small but complete primary polyps, whereas aboral halves develop into hollow spheres consisting of an ectodermal epithelium without endoderm (Fig. 4A,B) (Fritzenwanker et al, 2007;Lee et al, 2007). Four-day-old endoderm-free larvae developed morphologically normal sensory cells and ganglion cells in the ectoderm (Fig.…”

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

“…Wnt and Tcf transcripts are deposited in the oocyte and early embryo at the oral pole . In Hydractinia, and likewise in the thecate hydrozoan Clytia (Momose et al, 2008) and the anthozoan Nematostella (Fritzenwanker et al, 2007), this pole is the pole marked by the polar bodies, whereas in sea urchin embryos the transcripts are located at the opposite pole. Common denominator is that b-catenin stabilization co-localizes with cleavage initiation and gastrulation.…”

A conserved function for Strabismus in establishing planar cell polarity in the ciliated ectoderm during cnidarian larval development

“…CheStbm probe was transcribed from the EST clone SA0AAB22YG08 (GenBank ID CU429033) with T7 RNA polymerase. SEM was performed as described previously (Fritzenwanker et al, 2007).…”