Ordered progression of nematogenesis from stem cells through differentiation stages in the tentacle bulb of Clytia hemisphaerica (Hydrozoa, Cnidaria)

Abstract

Nematogenesis, the production of stinging cells (nematocytes) in Cnidaria, can be considered as a model neurogenic process. Most molecular data concern the freshwater polyp Hydra, in which nematocyte production is scattered throughout the body column ectoderm, the mature cells then migrating to the tentacles. We have characterized tentacular nematogenesis in the Clytia hemisphaerica hydromedusa and found it to be confined to the ectoderm of the tentacle bulb, a specialized swelling at the tentacle base. Analysis by a variety of light and electron microscope techniques revealed that while cellular aspects of nematogenesis are similar to Hydra, the spatio-temporal characteristics are markedly more ordered. The tentacle bulb nematogenic ectoderm (TBE) was found to be polarized, with a clear progression of successive nematoblast stages from a proximal zone (comprising a majority of undifferentiated cells) to the distal end where the tentacle starts. Pulse-chase labelling experiments demonstrated a continuous displacement of differentiating nematoblasts towards the tentacle tip, and that nematogenesis proceeds more rapidly in Clytia than in Hydra. Compact expression domains of orthologues of known nematogenesis-associated genes (Piwi, dickkopf-3, minicollagens and NOWA) were correspondingly staggered along the TBE. These distinct characteristics make the Clytia TBE a promising experimental system for understanding the mechanisms regulating nematogenesis.

Nematogalectin, a nematocyst protein with GlyXY and galectin domains, demonstrates nematocyte-specific alternative splicing in Hydra

“…Expression of both Ch-nemgal A and B transcripts was detected in the tentacle bulbs (Fig. S8 A-D), where nematocytes proliferate and differentiate (17). Weaker signals were also found at the margin of the mouth, where the population of differentiating nematocytes is less dense than in the tentacle bulb.…”

Scleractinian coral cell proliferation is reduced in primary culture of suspended multicellular aggregates compared to polyps

“…Within the phylum Cnidaria, this method is commonly used in hydrozoans, for example in the marine species Hydractinia echinata and Clytia hemisphaerica, in short-term pulse (5 mM BrdU for 30 min to a few hours)-chase assays to detect mitotic activity and cellular self-renewal (Müller et al 2004;Denker et al 2008). In adult colonies of scleractinian corals the BrdU labeling method has recently been used, at much lower concentrations and longer exposure periods, to investigate cell proliferation activity in aquariumbased studies.…”

A safer, urea-based in situ hybridization method improves detection of gene expression in diverse animal species

“…We thus chose to compare the expression patterns for minicollagen 3/4a (Denker et al, 2008), RFamide, and DRGX (Kraus et al, 2015). In all cases, formamide and urea variants gave comparable expression patterns, demonstrating that 4M urea could efficiently substitute for the 50% formamide during hybridization steps.…”

“…The in situ hybridization technique is a well-established method for RNA detection in the hydrozoan Clytia hemisphaerica, and has proven valuable for assessing gene expression during embryonic development, oogenesis, and in adult structures such as in the tentacle bulb (Chevalier et al, 2006;Denker et al, 2008;Leclère et al, 2012;Lapébie et al, 2014;Kraus et al, 2015).…”