Friday, August 29, 2008

Medicines from Monotremes

Somewhere in Eastern Australia, I stand on a darkened riverbank, huddled against the frigid wind. It is 2am, and I’m holding a small animal in my hands. It is covered with furry, loose skin, makes a growl like an angry cat, and tries to chew my hand with its soft, duck-like bill. The cold and the early hour are causing my mind to wander, and as I hold the squirming platypus, I reflect on the millions of years of evolution that have led to the strange creature I see before me.

Platypuses and echidnas are members of an ancient group of mammals called Monotremes, which have been around for 166 million years. They lay eggs like a reptile and produce milk like all mammals, and in the case of platypuses, produce venom like a snake, making them very unusual indeed. Little wonder that when platypuses were first discovered they were thought to be the trick of a taxidermist!

I am here on the riverbank to collect samples of platypus genetic material, which I’m going to use to unlock the secrets of its evolution, and maybe even help humans a little along the way. My research involves examining the genes of the platypus to help with understanding how mammals first evolved from their reptilian ancestors. Geneticists like me can investigate how traits like egg-laying were superseded by features such as milk production, and by looking at genes that are in both platypuses and modern mammals like humans, can also work out which genes are really important for us mammals. Although you won’t find humans sprouting a duck-bill any time soon, you might be astonished to learn that more than 80% of the platypus genes are also found in the human genome. In particular we can examine the genes involved in platypus immunity and learn more about how mammalian immune systems function and have evolved. Perhaps we may discover new ways of boosting our own immune systems.

My colleagues and I are studying the platypus genes that code for antimicrobial proteins. Unlike humans, platypus young are born after a short gestation in an immature state. They thus have a very underdeveloped immune system, and yet these fingernail-sized hatchlings still manage to survive in a dirty burrow that is full of microbes. Our team is investigating the possibility that platypus milk contains antimicrobial proteins which protect the developing young from infection. In the future, I hope it will be possible to duplicate these ‘natural antibiotics’ to develop new treatments for human diseases, which are urgently needed to combat existing antibiotic resistant pathogens.

We are also researching another bizarre feature of the platypus: its venom. Males have sharp spurs on each hind leg that are used to deliver a potent chemical poison into victims. Venom is used during fighting between males, but it can also be used for defence against potential predators like foxes and domestic dogs, which if spurred may die, and the occasional unwary human like me! Luckily, the animal I’m holding is a female so has no spurs, because in humans, envenomation causes terrible swelling and excruciating pain that is not relieved by morphine. There must be some very interesting and novel chemicals in the venom to cause such unusual symptoms. I am working to identify the chemicals by decoding the genes that produce them. Snake venoms have already been used to develop drugs to treat human diseases, and I’m hoping that our platypus venom research might also lead to the development of novel drugs. In particular, if we can find the platypus venom chemicals that cause the extreme pain, we may discover new pain receptors and be able to develop novel painkillers to block them.

A shout from a colleague reminds me that it’s time now for my platypus to have her blood sampled. From this I will be able to extract and study her DNA. The procedure is over quickly, and I take her down to the water to release her. She gives one parting growl, and then slips quietly under the water, apparently unaware of the great potential of her genes to help us improve human medicine.

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