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Le Micotossine

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Le Micotossine CNIDARIA • Radially symmetric • Dimorphic: two body forms (except for Anthozoa) – Polyp • Sessile, cylindrical body, ring of tentacles on oral surface – Medusa • Flattened, mouth-down version of polyp • Free-swimming • ~10,000 species • Marine animals • Only few freswater (Hydra) CNIDARIA • Basic body plan of ALL cnidarians – Sac with a central digestive compartment (GVC) – Single opening serving as both mouth and anus – Ring of tentacles on oral surface – Ectoderm and endoderm separated by acellular mesoglea CNIDARIA • All cnidarians are carnivores – Tentacles capture and push food into mouth – Tentacles are armed with stinging cells • Cnidoblasts / cnidocytes • Contain capsules (nematocysts) – The tentacle is stimulated (on “trigger”) – Nematocyst is discharged on the prey • Some species produce toxins (Injection of the toxin) CNIDARIA CNIDARIA • Different types of nematocystis: • Generic nematocyst (all) – Double-walled capsule with toxic mixture of phenols + proteins – Spines or barbs for penetration, anchor in victim • Spirocyst (Anthozoa) – Spring-like mechanism – Adhesive tubules wrap around and stick to victim • Ptychocyst (tube anemones) – Sticky nematocyst CNIDARIA • Prey is forced into the GVC • Extracellular digestion begins (coelenteron) – Enzymes secreted into GVC • Intracellular digestion completes process – Partially digested food engulfed by endoderm cells Phylum CNIDARIA • Anthozoa – Subclass Hexacorallia – Subclass Octocorallia • Cubozoa • Hydrozoa – Subclass Hydroidolina – Subclass Trachylina • Scyphozoa • Staurozoa CLASS ANTHOZOA • Anemones and corals • Lack medusa form • Gonads endodermal (found in the gastrodermis). • Form colonies • Exclusively marine CLASS ANTHOZOA • Subclass Hexacorallia – Hexacorallia = 6-fold symmetry (6x tentacles) – Both anemone and hard corals • Hard corals precipitate Ca3(CO3)2 from sea water to produce skeletal structures (coral reefs): exoskeleton • Contain symbiotic dinoflagellates – Zooxanthella CLASS ANTHOZOA • Zooxanthella: – Unicellular microalgae able to live in symbiosis with marine invertebrates – The majority belongs to the genus Symbiodinium and Amphidinium – Photosynthetic organisms (chlorophyll a and c) and the dinoflagellate pigments peridinin and diadinoxanthin. – Provide their host with the organic carbon products of photosynthesis (up to 90% of their host's energy needs for metabolism, growth and reproduction) – In return, they receive nutrients CLASS ANTHOZOA • Subclass Octacorallia – Octacorallia = 8-fold symmetry (8x tentacles) – Soft corals • Form complex tube-like skeletal structures • Lack zooxanthella Class Anthozoa Subclass Subclass Hexacorallia Octacorallia Sea fans Sea whips Sea pens Organ pipe coral Precious gold coral Order Order Order Order Zoanthidae Actinaria Scleractinia Antipatharia Zoanthids Sea anemones Stony corals Precious black coral Wire coral CLASS ANTHOZOA – TOXIC SPECIES • Hard corals: – Hard corals can cause abrasion injuries if a swimmer simply brushes against them – Certain coral colonies also possess stinging nematocysts which can leave a rash if touched (i.e. Goniopora) CLASS ANTHOZOA – TOXIC SPECIES • Soft corals: – Zoanthus and Palythoa (Indo Pacific) • Anemones: – Actinia equina (eastern Atlantic) – Condylactis gigantea (Red Sea, death) CLASS CUBOZOA • Name means «cube animals» • Box-shape medusa stage • Generally live in tropical oceans • They are equipped with highly toxic cnidocytes CLASS CUBOZOA • Polyps and medusae stages, but medusae dominate with polyp stage reduced. – polyp stage develops directly into medusa. • Tetramerous radial symmetry; bell cube-shaped with tentacles arising from each corner. • Gonads endodermal • Includes some 15 marine species. • Includes box jellies and sea wasps. CLASS CUBOZOA – TOXIC SPECIES • The most dangerous cnidarians – Most stings result in only a short-lived burning sensation but can be dangerous if the swimmer has a severe allergic reaction – Some species of jellyfish can be fatal • Several species of box jellyfish have been implicated in human deaths: – Chiropsalmus quadrigatus (20–50 deaths/year in the Philippines) CLASS CUBOZOA – TOXIC SPECIES • Chironex fleckeri (tropical waters of Australia): – The most venomous of all marine creatures: respiratory failure may occur within few minutes – Size of human head with tentacles up to almost 3 meters long – 5-7 meters of tentacles can deliver enough poison to kill in <5 min CLASS HYDROZOA • Most varied and derived of the cnidarian groups – Includes freshwater species (Hydra spp) • Polyps and medusa stage (polyp is dominant) – Examples of polyp-only forms (hydra) – Examples of medusa-only forms • Tetramerous radial symmetry • Gonads are ectodermal (found in the epidermis) • Solitary or colonials CLASS HYDROZOA • Colony of specialized hydranths: – Gonozooids: reproduction – Gastrozooids: feeding – Dactylozooids: catching prey CLASS HYDROZOA – TOXIC SPECIES • Most of the 2700 species of hydrozoa are harmless, but some can inflict painful injuries on humans – Millepora alcicornis (fire corals) have nematocysts that can cause a painful skin rash (Indo-Pacific, Red Sea and the Caribbean) – Aglaophenia cupresina (fire-weed) causes a nettle-like rash lasting several days (Indo- Pacific) CLASS HYDROZOA – TOXIC SPECIES • Physalia spp. (Portuguese man-of-war) is a free-swimming colony of openwater hydrozoans that lives at the sea–air interface. – Different species of Physalia are widespread throughout all oceanic regions, except the Arctic and Antarctic – May be blown onto beaches in swarms after strong onshore winds – The nematocysts remain active even when beached. – The tentacles may reach a length of up to 10 metres. – Physalia physalis is the most dangerous and has been responsible for some severe stings and few deaths CLASS SCYPHOZOA • Typically jellyfish • Most have atypical dimorphic life cycle – Polyp stage is atypical – Majority of life cycle spent in medusa form • Tetramerous radial symmetry. • Gut divided into a complex system of radial canals. • Some with a simple single mouth, but many with thousands of microscopic “mouths” at the ends of oral arms. • Gonads endodermal (found in the gastrodermis). CLASS SCYPHOZOA – TOXIC SPECIES • All jellyfish are capable of stinging, but only a few species are considered a significant hazard to human health: – Stomolophus nomurai – Sanderia malayensis • Species of some genera, such as Cyanea, Catostylus and Pelagia, may occur in large groups or swarms CNIDARIA– TOXIN • Analytical and clinical observations have established the toxicological diversity of cnidarian venoms – high molecular weight proteins – enzymes – hemolysins – non-proteinaceous compounds (e.g. purines, biogenic amines) • Some toxins identified previously in other venomous animals comprise the venom arsenal of cnidarians CNIDARIA– TOXIN Palytoxins Anthozoa Na+/K+ ATPase opening 2-3 PORE-FORMING TOXINS (PFTs) • Present in all cnidarian venoms • The mechanism of action is their penetration through the target cell membrane – Leakage of small molecules and solutes – Osmotic imbalance and cell lysis • PFTs exhibit dual structure – A stable water-soluble structure: monomeric and binds to the receptors on the target cell – A membrane-bound structure: oligomeric molecules forming integral membrane pores • PFTs are classified in two groups based on their secondary structure: α-PFTs and β-PFTs PORE-FORMING TOXINS (PFTs) • α-PFTs and β-PFTs displays different mechanisms of pore formation: – α-PFTs: toroidal mode • Requires a protein binding to stabilize – β-PFTs: toroidal pore or octameric pore • No role of lipids in the pore wall is necessary • High stability of β-barrel is assured by interstrand hydrogen bonds ACTINOPORINS • α-PFTs present in Anthozoa and Hydrozoa • Mediate various types of toxicity and bioactivity all caused by a pore-forming mechanism: – Cardiovascular and respiratory arrest in rats – Lysis of chicken, goat, human and sheep erythrocytes • The best characterized are: – Equinatoxin II from the sea anemone Actinia equina ACTINOPORINS – Sticholysin I and II from the anemone Stichodactyla helianthus – Fragaceatoxin C from the anemone Actinia fragacea. ACTINOPORINS • The mechanism of membrane penetration requires several steps: – Initial binding to the target membrane • Specific recognition of sphingomyelin using aromatic rich region – Insertion of the N-terminal amphiphilic α-helix segment to the lipid membrane – Oligomerization on the surface of the membrane • α-helices of 3 or 4 monomers insert into the membrane and form the ion conductive pathway – This last step is most likely arranged in a toroidal pore mode JELLYFISH TOXINS (JFTs) • Cubozoan-related porins are the most potent and rapid-acting toxins secreted by jellyfish species • α-PFTs • Exhibit varying target specify towards various vertebrate tissue, dependent on the toxin member: – Cardiovascular collapse – Hemolytic • Toxin originally identified in Cubozoa species: – CaTX-A/B from Carybdea alata JELLYFISH TOXINS (JFTs) – CrTX-A/B from Carybdea rastoni – CqTX-A from Chiropsalmus quadrigatus – CfTX-1/2 and CfTX-A/B/Bt from Chironex fleckeri JELLYFISH TOXINS (JFTs) • Homologues of cubozoan porins were reported also in: Scyphozoa (Aurelia aurita) Hydrozoa (Hydra magnipapillata) Anthozoa (Aiptasia pallida) JELLYFISH TOXINS (JFTs) • The hypothetical mechanism involves oligomerization of several amphiphilic and hydrophobic α-helices in the N-terminal region of the toxin – distortion of the plasma membrane – cell death • The same mechanism stays at the basis of the hemolytic
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