Tentacle Morphogenesis Research Articles

Cell proliferation controls body size growth, tentacle morphogenesis, and regeneration in hydrozoan jellyfish Cladonema pacificum.

Jellyfish have existed on the earth for around 600 million years and have evolved in response to environmental changes. Hydrozoan jellyfish, members of phylum Cnidaria, exist in multiple life stages, including planula larvae, vegetatively-propagating polyps, and sexually-reproducing medusae. Although free-swimming medusae display complex morphology and exhibit increase in body size and regenerative ability, their underlying cellular mechanisms are poorly understood. Here, we investigate the roles of cell proliferation in body-size growth, appendage morphogenesis, and regeneration using Cladonema pacificum as a hydrozoan jellyfish model. By examining the distribution of S phase cells and mitotic cells, we revealed spatially distinct proliferating cell populations in medusae, uniform cell proliferation in the umbrella, and clustered cell proliferation in tentacles. Blocking cell proliferation by hydroxyurea caused inhibition of body size growth and defects in tentacle branching, nematocyte differentiation, and regeneration. Local cell proliferation in tentacle bulbs is observed in medusae of two other hydrozoan species, Cytaeis uchidae and Rathkea octopunctata, indicating that it may be a conserved feature among hydrozoan jellyfish. Altogether, our results suggest that hydrozoan medusae possess actively proliferating cells and provide experimental evidence regarding the role of cell proliferation in body-size control, tentacle morphogenesis, and regeneration.

Integrating Embryonic Development and Evolutionary History to Characterize Tentacle-Specific Cell Types in a Ctenophore.

The origin of novel traits can promote expansion into new niches and drive speciation. Ctenophores (comb jellies) are unified by their possession of a novel cell type: the colloblast, an adhesive cell found only in the tentacles. Although colloblast-laden tentacles are fundamental for prey capture among ctenophores, some species have tentacles lacking colloblasts and others have lost their tentacles completely. We used transcriptomes from 36 ctenophore species to identify gene losses that occurred specifically in lineages lacking colloblasts and tentacles. We cross-referenced these colloblast- and tentacle-specific candidate genes with temporal RNA-Seq during embryogenesis in Mnemiopsis leidyi and found that both sets of candidates are preferentially expressed during tentacle morphogenesis. We also demonstrate significant upregulation of candidates from both data sets in the tentacle bulb of adults. Both sets of candidates were enriched for an N-terminal signal peptide and protein domains associated with secretion; among tentacle candidates we also identified orthologs of cnidarian toxin proteins, presenting tantalizing evidence that ctenophore tentacles may secrete toxins along with their adhesive. Finally, using cell lineage tracing, we demonstrate that colloblasts and neurons share a common progenitor, suggesting the evolution of colloblasts involved co-option of a neurosecretory gene regulatory network. Together these data offer an initial glimpse into the genetic architecture underlying ctenophore cell-type diversity.

Functional studies on the role of Notch signaling in Hydractinia development

The function of Notch signaling was previously studied in two cnidarians, Hydra and Nematostella, representing the lineages Hydrozoa and Anthozoa, respectively. Using pharmacological inhibition in Hydra and a combination of pharmacological and genetic approaches in Nematostella, it was shown in both animals that Notch is required for tentacle morphogenesis and for late stages of stinging cell maturation. Surprisingly, a role for Notch in neural development, which is well documented in bilaterians, was evident in embryonic Nematostella but not in adult Hydra. Adult neurogenesis in the latter seemed to be unaffected by DAPT, a drug that inhibits Notch signaling. To address this apparent discrepancy, we studied the role of Notch in Hydractinia echinata, an additional hydrozoan, in all life stages. Using CRISPR-Cas9 mediated mutagenesis, transgenesis, and pharmacological interference we show that Notch is dispensable for Hydractinia normal neurogenesis in all life stages but is required for the maturation of stinging cells and for tentacle morphogenesis. Our results are consistent with a conserved role for Notch in morphogenesis and nematogenesis across Cnidaria, and a lineage-specific loss of Notch dependence in neurogenesis in hydrozoans.

Tentacle morphogenesis in hydra: II. Formation of a complex between a sensory nerve cell and a battery cell

Abstract Differentiation of sensory nerve cells in tentacles of Hydra magnipapillata was Investigated using the monoclonal antibody NV1. NV1+ sensory nerve cells form specific complexes with battery cells in tentacles. NV1+ cells can only be formed by differentiation from interstitial cell precursors. These precursors complete a terminal cell cycle in the distal gastric region at the base of tentacles; differentiation from the S/G>2 boundary to expression of the NV1 antigen requires 30 h. During this time, precursors move from the distal gastric region into the tentacles, differentiate to morphologically fully formed nerve cells and then begin expressing NV1 antigen. The neuropeptide head activator stimulates NV1+ differentiation in S-phase of the precursor’s cell cycle.

Tentacle morphogenesis in hydra: I. The role of head activator

Abstract Stimulation of tentacle-specific cell differentiation by the neuropeptide head activator was investigated in Hydra magnipapillata. Tentacle-specific sensory nerve cells were identified by a monoclonal antibody, NV1. Treatment of hydra with 1 pM head activator for 18 h stimulated differentiation of NV1+ nerve cells and tentacle epithelial cells in tissue from the distal gastric region. Head tissue and tissue from the proxmial gastric region did not respond to head activator treatment with increased NV1+ differentiation. Hence the distal gastric region appears to be the site of tentacle formation in hydra. Tentacle precursors in head tissue seem to be committed since they fail to respond to head activator or to changes in tissue size with altered amounts of tentacle formation. We suggest that NV1 precursors form a complex with tentacle epithelial cell precursors, which then moves distally through the head region into the tentacles. The signal for NV1+ differentiation appears to be formation of this complex.

Protein Patterns and Synthetic Profiles during Distal Regeneration in Hydra oligactis: (Hydra/regeneration/protein/mesoglea).

Protein patterns and synthetic profiles were examined during distal regeneration in Hydraoligactis. Electrophoretic and radioactive tracer analyses revealed qualitative changes in the general protein profile during regeneration, with a heightened period of protein synthesis between 27-30 hr of regeneration, immediately preceding emergence of the first pair of tentacles. Following this, an increase in collagen-rich mesogleal protein secretion was observed coincident with tentacle initiation. Inhibition of collagen secretion with the proline analog L-azetidine-2-carboxylic acid (LACA) inhibited tentacle formation, and resulted in the development of unique "hypostome buds" at the distal regeneration surface. At the cellular level LACA did not inhibit the nerve cell differentiation that normally precedes tentacle growth, although some predicted decline in cnidocyte production was noted. It is proposed that mesogleal collagen secretion and structural organization may play a major role in the mechanical aspects of Hydra tentacle morphogenesis.

Tentacle Morphogenesis in Hydra: A Morphological and Biochemical Analysis of the Effect of Actinomycin D

synopsis. Stalked hydra exposed to 3 /tg/ml actinomycin D for 24 hr exhibited a re? striction in the patterning of tentacle morphogenesis. The two-tentacled morphological modification manifested in regenerating hydra was correlated with a reduction both in RNA synthesis in the hypostomal region of the animal and in the DNA synthetic activity associated with normal tentacle elaboration. The tentacles formed on actino? mycin D-treated animals developed in the proper sequence, however. In time the modification disappeared, indicating that the effect was reversible. Histological studies demonstrated depleted interstitial cell (I-cell) populations along the body column of actinomycin D-treated hydra. Replacing the hypostomes of actino? mycin D-treated hydra with normal hypostomes reversed the cellular effects of actinomyin D exposure. All morphological and biochemical modifications in tentacle morphogenesis oc? curring after actinomycin D treatment were consistent with an impairment of hypo? stomal function in the animal. Evidence from 3H-actinomycin D autoradiography pro? vided support for the proposal that the nervous system was the morphological site of this malfunction. One of the most fundamental problems confronting developmental biologists today is that of morphogenesis, or the emergence of order resulting from the elaboration of form. Form, in living systems, reflects inter? actions ranging from the moiecuiar to the organismal levels of organization. Conse? quently, investigations of morphogenetic phenomena should include observations at multiple levels of organization. For years the freshwater Cnidarian hydra has provided an experimental sys? tem for studies of morphogenesis. In part, this results from the fact that morpho? genesis in hydra is a relatively restricted process. Normally, only a mouth, an oral ring of tentacles, and a basal disc are elaborated. Of these structures, the tentacles stand out with respect to both functional and developmental significance. Several components contribute to tenta? cle morphogenesis in hydra. At least one of these components must concern pattern

Tentacle morphogenesis in hydra : I. The morphological effect of actinomycin D.

Hydra oligactis exposed to 3 μg/ml actinomycin D for 24 hours regenerated only the first pair of tentacles (the mid-laterals). If left uncut, actinomycin D treated animals underwent a reduction of the normal number of tentacles to two or less.Inductive activity was retained in the 2-tentacled hypostomes. However, the tentacles present exhibited reduced capacities to capture and manipulate prey.Histological studies showed that the tentacles of actinomycin D treated hydra were morphologically identical to those of the controls. The interstitial cell (I-cell) population of the treated animals, however, became depleted. Replacing the hypostome of an actinomycin D treated hydra with a normal hypostome reversed the cellular effects of actinomycin D treatment.The modifications in tentacle morphogenesis occurring after actinomycin D treatment are consistent with an impairment of hypostomal function in the animal. It is suggested that the morphological site of this malfunction may be in the nervous system.