Model Organisms: The Hydra

The Hydra was first documented by the ancient Greeks as a many-headed serpent harboring a particular dislike towards certain sons of Zeus, for example Heracles (also known as Hercules). Perhaps the most intriguing of Hydra’s features was its regenerative abilities. It grew multiple heads in place of those chopped off. Although that didn’t stop Heracles…

Unsurprisingly, the multi-headed serpent isn’t the subject of modern scientific research. This is most likely due to the fact it doesn’t exist, it is a myth. However, the mythical Hydra has influenced the naming of a group of species (biological term - genus) that are of scientific interest. So what are these species? Well, they’re a group of non-motile freshwater animals about half an inch long. They essentially consist of a stalk; one end attached to a hard surface, the other ending in a ring of tentacles, which they use to sting, poison, and catch passing prey. Heracles, probably doesn’t need to lose much sleep.

Why the name Hydra? Although the Hydra do not appear to share many qualities with the ancient mythological creature, there is one, their astonishing regenerative ability. If you cut a Hydra in two, both halves will regenerate into two independent Hydras. But it doesn’t end there. Hydra cut into multiple pieces, and even Hydra that have been disaggregated (their cells have been dissociated from one another) are able to regenerate back into fully functional Hydra. Their stem cells show unlimited regenerative capabilities (they appear to be able to continue dividing forever). Another ‘quirky’ feature of the Hydra is their requirement to literally tear open their skin at the tentacle end of their stalk to generate a mouth each time they need to feed on prey.

Hydra are able to reproduce both sexually (fusion of male sperm and female egg) and asexually (where a newly formed Hydra buds from the stalk of a pre-existing one). Under normal conditions the majority of reproduction is asexual. When reproducing asexually Hydra do not appear to show any signs of aging (the organism doesn’t appear to have a fixed life span, so could be viewed as immortal!), although this changes upon entering sexual reproduction. In order to undergo sexual reproduction individuals must develop either male or female organs (sexual differentiation). On average, individuals survive only for four months after sexual differentiation. For readers familiar with Futurama, it appears Hydra are faced with a similar dilemma to Dr Zoidberg and his species…

These qualities make Hydra a potentially interesting group of species to study regeneration, development, and the process of aging. But what qualities make a good model organism? (This is by no means an exhaustive list).

  1. They should be easy to grow in large numbers in a research environment.

  2. They should have a fairly short life span.

  3. They should be able to be easily genetically manipulated.

Hydra’s ability to reproduce asexually makes it an easy organism to grow in research laboratories, and although it doesn’t appear to have a fixed life span, when well fed it produces new buds every two days. The simplicity of Hydra’s body plan also makes it an easy organism to study. The Hydra’s body is essentially made of two types of tissue, contains no specialised functional organs (eg heart, lungs…), and there are few different specialised cell types. The genome of Hydra magnipappilata (a species of Hydra) was recently sequenced, allowing insights into the genetic content and evolutionary origins of the aquatic animals.

However, their ability to be genetically manipulated has been lacking, greatly slowing research on a molecular level. Additionally, growing Hydra cells on their own outside the context of the body (in vitro) has proved to be very difficult. Nonetheless the future looks promising as progress has been made and genetically modified Hydra (modified to make a fluorescent protein) have been generated. Only time will tell what secrets we will unlock from the Hydra.

#AshleyPridgeon #Hydra #ModelOrganisms #Animals

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