A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa)

Benjamin Americus, Tamar Lotan, Jerri L. Bartholomew, Stephen D. Atkinson

Research output: Contribution to journalReview articlepeer-review

Abstract

Myxozoans are obligate parasites that have complex life cycles requiring alternate vertebrate and invertebrate hosts, with transmission via microscopic waterborne spores. Unusually for parasites, they belong to the phylum Cnidaria, alongside thousands of free-living corals, sea anemones, jellyfish and hydrozoans. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called “polar capsules” in myxozoan research. Free-living cnidarians utilise this cellular weaponry for defence, predation and adhesion, whereas myxozoans use it to anchor to their hosts as the first step in infection. Despite the ~650 million years of divergence between free-living cnidarians and myxozoans, their nematocysts retain many shared morphological and molecular characters. Both are intra-cellular capsules with a single opening, and contain a coiled, evertable tubule. They are composed of unique nematocyst proteins, nematogalectin and minicollagen, and both likely contain an internal matrix of metal cations covalently bound to the anionic polymer poly-gamma glutamate. The rapid dissociation of this matrix and the resulting increase in internal osmotic potential is the driving force behind tubule elongation during discharge. In this review, we compare the structure and function of nematocysts in Myxozoa and free-living Cnidaria, incorporating recent molecular characterizations. We propose that terminology for homologous myxozoan structures be synonymized with those from other Cnidaria, hence, “polar capsule” as a taxon-specific nematocyst morphotype and “polar filament” as “tubule.” Despite taxonomic divergence, genome reduction and an evolution to parasitism, myxozoans maintain nematocysts that are structurally and functionally homologous to those of their free-living cnidarian relatives.

Original languageEnglish
Pages (from-to)763-769
Number of pages7
JournalInternational Journal for Parasitology
Volume50
Issue number10-11
DOIs
StatePublished - Sep 2020

Bibliographical note

Funding Information:
This work was supported by the United States-Israel Binational Agricultural and Development fund grant number IS-5001-17C0. Tubifex tubifex infected with M. cerebralis were provided for this study by George Schisler, Colorado Parks and Wildlife, Parvin Lakes Research Laboratory, USA. Scanning electron microscopy was performed by Theresa Sawyer at the Electron Microscopy Facility of Oregon State University, USA.

Funding Information:
This work was supported by the United States-Israel Binational Agricultural and Development fund grant number IS-5001-17C0 . Tubifex tubifex infected with M. cerebralis were provided for this study by George Schisler, Colorado Parks and Wildlife, Parvin Lakes Research Laboratory, USA. Scanning electron microscopy was performed by Theresa Sawyer at the Electron Microscopy Facility of Oregon State University, USA.

Publisher Copyright:
© 2020 Australian Society for Parasitology

Keywords

  • Cnidaria
  • Myxosporean
  • Myxozoan
  • Nematocyst
  • Polar capsules
  • Poly-gamma glutamate
  • Tubule

ASJC Scopus subject areas

  • Parasitology
  • Infectious Diseases

Fingerprint

Dive into the research topics of 'A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa)'. Together they form a unique fingerprint.

Cite this