Search

Dorsal root ganglion (DRG) neurons are the predominant cell type that innervates the vertebrate skin. They are typically described as pseudounipolar cells that have central and peripheral axons branching from a single root exiting the cell body. The peripheral axon travels within a nerve to the skin, where free sensory endings can emerge and branch into an arbor that receives and integrates information. In some immature vertebrates, DRG neurons are preceded by Rohon-Beard (RB) neurons. While the sensory endings of RB and DRG neurons function like dendrites, we use live imaging in zebrafish to show that they have axonal plus-end-out microtubule polarity at all stages of maturity. Moreover, we show both cell types have central and peripheral axons with plus-end-out polarity. Surprisingly, in DRG neurons these emerge separately from the cell body, and most cells never acquire the signature pseudounipolar morphology. Like another recently characterized cell type that has multiple plus-end-out neurites, ganglion cells in Nematostella, RB and DRG neurons maintain a somatic microtubule organizing center even when mature. In summary, we characterize key cellular and subcellular features of vertebrate sensory neurons as a foundation for understanding their function and maintenance., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The cadherin-catenin complex is a conserved, calcium-dependent cell-cell adhesion module that is necessary for normal development and the maintenance of tissue integrity in bilaterian animals. Despite longstanding evidence of a deep ancestry of calcium-dependent cell adhesion in animals, the requirement of the cadherin-catenin complex to coordinate cell-cell adhesion has not been tested directly in a non-bilaterian organism. Here, we provide the first analysis of classical cadherins and catenins in the Starlet Sea Anemone, Nematostella vectensis. Gene expression, protein localization, siRNA-mediated knockdown of α-catenin, and calcium-dependent cell aggregation assays provide evidence that a bonafide cadherin-catenin complex is present in the early embryo, and that α-catenin is required for normal embryonic development and the formation of cell-cell adhesions between cells dissociated from whole embryos. Together these results support the hypothesis that the cadherin-catenin complex was likely a complete and functional cell-cell adhesion module in the last common cnidarian-bilaterian ancestor. SUMMARY STATEMENT: Embryonic manipulations and ex vivo adhesion assays in the sea anemone, Nematostella vectensis, indicate that the necessity of the cadherin-catenin complex for mediating cell-cell adhesion is deeply conserved in animal evolution., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Nervous systems often consist of a large number of different types of neurons which are generated from neural stem and progenitor cells by a series of symmetric and asymmetric divisions. The origin and early evolution of these neural progenitor systems is not well understood. Here we use a cnidarian model organism, Nematostella vectensis, to gain insight into the generation of neural cell type diversity in a non-bilaterian animal. We identify NvFoxQ2d as a transcription factor that is expressed in a population of spatially restricted, proliferating ectodermal cells that are derived from NvSoxB(2)-expressing neural progenitor cells. Using a transgenic reporter line we show that the NvFoxQ2d cells undergo a terminal, symmetric division to generate a morphologically homogeneous population of putative sensory cells. The abundance of these cells, but not their proliferation status is affected by treatment with the γ-secretase inhibitor DAPT, suggesting regulation by Notch signalling. Our data suggest that intermediate progenitor cells and symmetric divisions contribute to the formation of the seemingly simple nervous system of a sea anemone., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The sea anemone Nematostella vectensis (Nv) is a leading model organism for the phylum Cnidaria, which includes anemones, corals, jellyfishes and hydras. A defining trait across this phylum is the cnidocyte, an ectodermal cell type with a variety of functions including defense, prey capture and environmental sensing. Herein, we show that the Nv-NF-κB transcription factor and its inhibitor Nv-IκB are expressed in a subset of cnidocytes in the body column of juvenile and adult anemones. The size and distribution of the Nv-NF-κB-positive cnidocytes suggest that they are in a subtype known as basitrichous haplonema cnidocytes. Nv-NF-κB is primarily cytoplasmic in cnidocytes in juvenile and adult animals, but is nuclear when first detected in the 30-h post-fertilization embryo. Morpholino-mediated knockdown of Nv-NF-κB expression results in greatly reduced cnidocyte formation in the 5 day-old animal. Taken together, these results indicate that NF-κB plays a key role in the development of the phylum-specific cnidocyte cell type in Nematostella, likely by nuclear Nv-NF-κB-dependent activation of genes required for cnidocyte development., (Copyright © 2012 Elsevier Inc. All rights reserved.)

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.

Gastrulation is a central event in metazoan development, involving many cellular behaviors including invagination, delamination, and ingression. Understanding the cell biology underlying gastrulation in many different taxa will help clarify the evolution of gastrulation mechanisms. Gastrulation in the anthozoan cnidarian Nematostella vectensis has been described as a combination of invagination and unipolar ingression through epithelial to mesenchymal transitions (EMT), possibly controlled by snail genes, important regulators of EMT in other organisms. Our examination, however, fails to reveal evidence of ingressing cells. Rather, we observe that endodermal cells constrict their apices, adopting bottle-like morphologies especially pronounced adjacent to the blastopore lip. They retain apical projections extending to the archenteron throughout gastrulation. Basally, they form actin-rich protrusions, including interdigitating filopodia that may be important in pulling the ectodermal and endodermal cells together. Endodermal cells retain cell-cell junctions while invaginating, and are organized throughout development. Never is the blastocoel filled by a mass of mesenchyme. Additionally, injection of splice-blocking morpholinos to Nematostella snail genes does not result in a phenotype despite dramatically reducing wild-type transcript, and overexpression of Snail-GFP in different clonal domains has no effect on cell behavior. These data indicate that EMT is not a major factor during gastrulation in Nematostella.