Sexy Finger - Part Two
Last time, I talked about how the length of your 4th finger (that's the one next to the little finger) can give a strong hint about the level of your male or female sex hormones. It's because of the "homeobox" - a small section of your DNA that makes sure that your arms go at the top of your chest (not the bottom), and your hands go on the end of your arms (not your legs). The same bit of the homeobox that assembles your hands also governs your reproductive potential. When the homeobox goes wrong, it can cause diseases. But if we learn how to tweak the homeobox, we could stop these problems, and, maybe grow new body parts.
Today, Saint Cosmos and Saint Damian are the patron saints of Surgeons. They got this exalted status from a famous painting by the 15th-Century Spaniard, Alonso de Sedano. He painted what looks like the first transplant surgery operation. It shows Doctors Cosmos and Damian performing a miracle - they are removing a white cancerous leg, and replacing it with a black leg from a dead Moor (a Moslem of African descent). That was a pretty impressive trick - but wouldn't it be a lot easier and safer if instead, you could just grow a new leg, where the old leg used to be?
Well, one day we might be able to, if the 1995 Nobel Prize for Physiology or Medicine is anything to go by. It was given to three biologists for their research into the homeobox. One of them, Edward B. Lewis had been working with fruit flies since the 1940s. The other two, Christiane Nüsslein-Volhard and Eric F. Wieschaus had begun their work in the 1970s.
Now the fruit fly body is made up of repeating segments that are customised to perform special tasks. There are three segments that each have a pair of legs, one segment that sprouts wings, and another segment for the antennae on the head. But biologists have, every now and then, seen sporadic errors in how the segments got made and arranged - they've seen the occasional mutated fruit fly with legs growing on its head where the antennae should be. The fault was found in the homeobox.
The three biologists got their Nobel Prize for working out which of the particular genes in the fruit fly DNA control the extraordinary change from a single fertilised egg to a fully-fledged fruit fly. The three biologists had discovered that these genes were in the homeobox.
We think that the homeobox is involved in a few minor human malformations. For example, most of us have 12 ribs on one side and 12 ribs on the other. But some of us have 13 ribs on one side and 12 on the other - and that's probably a homeobox "thing".
Another human malformation is craniosynostosis. When a baby is born, the flat plates of bone that make up the skull actually overlap each other to make the head smaller, so the baby can squeeze through the birth canal. These bones gradually come closer during the early years of life and fuse together. Craniosynostosis is when these gaps between the flat bones fuse shut too early. The baby's brain wants to keep on growing bigger, but the skull won't expand - and things can get really messy. In this case, the treatment is just simply to remove the bits of bone that are joined together, and insert a polyethylene film barrier to stop the bones from fusing back together again. We think that craniosynostosis, this premature fusion of the gaps between the bones of the skull, is related to an error of the homeobox.
We also think that retinoic acid, a chemical related to vitamin A, interferes with the homeobox. That's why pregnant women should not take too much vitamin A.
In the year 2002, we humans will have mapped all of the human DNA. We will have thoroughly explored the homeobox region of our DNA. And maybe then we'll be able to re-grow limbs that were lost in accidents, instead of fitting artificial limbs.
But people being what they are, there'll be plenty of interest in seeing if we can extend the length of the fourth finger....
Published 07 September 1999
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