Biodiversity Project

Mike Walker

    Radiata is a group of invertebrates which consists of two phyla, Cnidaria and Ctenophora.  Radiata includes exclusively aquatic organisms that are fierce predators for their level of intellectual complexity.  The Cnidarians and Ctenophorans are categorized together due their radial symmetry and stinging organelles. (Campbell 643) 

Freshwater hydra

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http://www.microscope-microscope.org/gallery/hydra-187h.jpg

            The hydra, one of the few freshwater Radiata, has one of the most complex prey capture and survival systems in the world. (Wikipedia)  The hydra is closely related to the Portuguese Man-O-War and the fire coral.  Hydra are sort-bodied, sessile organisms, meaning that they cannot move on their own accord.  Because of this lack of self-locomotion, hydra cannot simply "track down" their prey.  They must depend on bodily chemicals for prey capture and defense mechanisms.  These chemical allomones are dispersed throughout each individual hydra:  in its stinging cells (nematocytes), body column, and other specialized aggression organs.  Hydrae make use of many allomones, such as:  neurotoxins, cytolysins (extracellular protein), and toxic phospholipids.  Hydrae also express additional proteins, among them:  CRISP proteins, Prokineticin-like polypeptides, and toxic deoxyribonucleases.  These chemical allomones are produced and stored in a glandular tissue and delivered through a hydra’s venom apparatus.

            Hydra have both offensive and defensive allomones.  The offensive allomones are used to paralyze and subdue prey, whereas the defensive ones are used to fend off enemies.  Hydrae are dependent on allomones because they have extremely fragile bodies, and must therefore rely on chemical, not physical, processes to capture prey and to prevent from being preyed on.  Their chemical excretory system is very advanced, utilizing neurological ion modifiers, enzymes and pore-forming cytolytic proteins.

            Until recently, the hydra genome has been largely unresearched.  A large scale genome sequencing project (the Hydra EST Project) has begun sequencing the Hydra magnipapillata ,which is a species of hydra with an estimated 13,000 genes. (Sher 867)  The bioinformatic work was carried out from May to August of 2004, at theGenome Sequencing Center at Washington University.  The EST Project used a existing database to compare the hydra’s amino acid venom sequences to the known sequences for the venom components of non-Cnidarians in order to show thediversity of the hydra allomonal system.

Diversity of the Hydra Allomone System

Table 1.

(Sher 870)

This table shows the uniqueness of the hydra allomonal system. In the first column, the name of a hydra allomone is given.

In the column two, the type of organism that has a similar allomone is stated.  Column three states the effects of that allomone.

            Hydra were found to have fifty-eight distinct sequences of allomones, which were divided into fifteen families.  The EST Project also used an existing database to compare the hydra’s amino acid venom sequences to the known sequences for the venom components of other Cnidarians.  In this comparison, eight groups revealed a distinct similarity.  Since these venoms were previously studied, they could be examined further.

            Kalicludines are a group of neurotoxins in hydrae, which are also found in sea anemones.  Kalicludines belong to a superfamily of polypeptides that code for other proteins, including protease inhibitors and growth factors.  When injected into prey, these toxins are capable of simultaneously blocking the K⁺ channels and activating the Na+ channels of the organism, rendering the prey completely immobilized.  This injection is similar to that of a massive electric shock. 

            Three groups of hydrae cytolytic toxins are related to those from sea anemones and box jellyfish.  These toxins create pores in target animal membranes, along with neurotoxin effects.  These toxins are the same ones involved in the Portuguese Man-O-War’s deadly stings.

            One of the hydra’s toxic phospholipase allomones originated with the jellyfish species, Rhopilema nomadica.  This toxin can be used to probe an organism to detect a route of venom delivery.  Hydrae have a 38-47% identical sequence for this toxin to the jellyfish.  Other hydrae toxic phosphlipases can be compared to the venom of the honeybee, the Gila Monster, and scorpions.

             CRISP (Crystein RIch Secretory Protein) proteins are not directly toxic allomones for hydra.  These proteins are found in plants, which utitlize them for disease fighting.  Hydrae have signal peptides related to CRISP proteins, which makes it likely they are secreted as part of the allomonal system.

            The hydrae proteins that are shared by spiders, Prokineticin-like proteins, don’t have an overtly toxic nature.  These proteins are used in smooth muscle contraction and relaxation.  However, in study, it has also been shown that these proteins can induce hyperalgesia, an extreme sensitivity to pain.  Hydra utilize this by injecting it into its prey, immobilizing the organism with pain, therefore allowing time for the hydra to consume the organism.  These proteins are also found in the venoms of scorpions and spiders.

            The final hydrae proteins examined in this project were deoxyribonucleases.  These molecules cause enzymes to release purines, which perform many biological functions, including the suppression of motor neurons.  It is uncertain whether hydra venom is significantly affected by the presence of deoxyribonulceases, but the protein has been found in many nematocyst extracts.

            Animal venoms fall into three general categories:

                        1.  Neurotoxic venoms that induce cardiovascular or respiratory problems at the site of injury

                        2.  Tissue-damaging venoms that induce local biological problems

                        3.  Pain producing venoms (Sher 876)

            Most organisms have venoms that only serve one purpose.  Hydra venom is capable of falling in all of the categories.  Hydrae can induce neurological problems, damage body tissue and disable enzymes, or cause extreme pain.

            The diversity of hydra venom leads to the possibilities that it could be used in many different capacities.  As shown in Table 1, hydrae have venom orthologs with different species of snakes.  Due to this similarity, hydra venom could have similar applications to those of snake venoms.  Within the past five years, snake venoms have been found to be a possible treatment for heart attack and stroke victims. (BBC News)  Heart attacks and strokes are caused by a clogging of the arteries with fatty material, which weakens blood vessel walls and leads to blood clots.  Snake venom has been shown to be able to bring on or stop this process.  Snake venom appears to be a great aid in the treatment of heart attacks and strokes, and hydra venom would be a great candidate for this task as well.  The EST Project did not plan on increasing it's effort to include the determination of possible disease that hydra venom could treat.  However, it's very possible that hydra venom can treat some forms of stroke that snake venom couldn't.  Further research is needed to determine if/how hydra venom could allow us to treat some of our most fatal medical conditions.

            The most confounding observation of the EST Project was that hydra seem to also have allomonal proteins in non-nematocystic tissue.  Why?  Why would an organism have offensive and defensive biological chemicals in tissue that it will not be used on other organisms?  The most likely explanation is that hydra have proteins that have a duality of allomonal and endogenous roles.  For example, the PLA2 proteins of the hydra have both toxic and digestive roles.  This is an uncommon trait.  Most organisms with external allomonal systems maintain separate proteins for allomonal and endogenous functions.

            The hydra, a “simple” cnidarian, possess an immensely complex allomonal system, which it uses to catch prey and deter enemies.  The many different proteins each perform slightly different processes for the hydra allmonal system.  Hydrae are as chemically advanced as any other organism, and very well adapted at surviving in aquatic environments.

Glossary

    Allomone - A biological chemical that is produced by one organism in order to be used on another organism, for offensive or defensive purposes

    Endogenous - A protein that is produced and used exclusively within an organism, with no reaction to the outside environment

    Enzymes - A type of protein that catalyzes (speeds up) a reaction, generally inside the body of a living organism

    K+ channel - A electrochemical system that involves the changing of concentration of potassium ions in the brain.  This channel is involved in neural signaling and for the generation of the cardiac rhythm

    Na+ channel - A electrochemical system that is responsible for the transport of sodium ions through the membrane. The pore region is generally conserved and is essential for the specificity of the channel.

    Nematocytes - Cells that make up the hydra stinging organelle involved in catching prey

    Orthologs - Genes that code for proteins with a similar function, but exists in different species

    Proteins - A group of complex organic molecules that consist of amino acids joined together by peptide bonds

References

Campbell, Neil A. and Jane B. Reece.  Biology.  “Cnidarians have Radial Symmetry, a Gastrovascular Cavity, and Cnidocytes.”  643-644.  2005.

“Cnidaria.”  Wikipedia.  <http://en.wikipedia.org/wiki/Cnidaria>

Sher, Daniel et al.  “Toxic Polypeptides of the Hydra - a Bioinformatic Approach to Cnidarian Allomones."  Toxicon 45.  (2005:  865-879).

"Snake Venom for Heart Attacks."  BBC News.  9 July 2002.  <http://news.bbc.co.uk/1/hi/health/2118265.stm>

Additional Sources

http://www.hydrabase.org - Information on the Hydra Genome Project

www.sciencedirect.com/science - Original Article (Search for "Toxic Polypeptides of the Hydra" OR Daniel Sher)

http://www.personal.psu.edu/users/m/a/mas810/bioprojindex4.html - "Eating Habits of the Simple Hydra: Not So Simple." by Maggie Sikora

                                                                                                         A scientific review of the digestive traits of the hydra