Reinventing the Ark

A glow-in-the-dark rabbit, a goat with spider-web silk in its milk, pigs that are living factories for drugs like insulin, this is not the stuff of science fiction.

Indeed, the science behind these strange creatures, which involves transferring a gene from one species to another, is increasingly common.

This week, NATALIE SOH finds out some tricks that let scientists play with Mother Nature.

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WITH genetic engineering, rabbits and zebra fish have been coaxed by researchers to glow, with help from a fluorescent substance that originally lit up a jellyfish.

And using similar techniques, scientists have taken genes from humans and added them to tiny, benign bacteria so they can churn out the insulin needed to treat patients with diabetes.

 

Zebra fish fry that glow

Genetically, the stuff made by the bacteria factories is no different from the hormone secreted in the human pancreas, which is necessary to control blood-sugar levels. Human insulin has been produced on a large scale with a little help from the Escherichia coli, or E. coli, bacterium since the 1980s.

Here's one way of cutting genes from one species and pasting them onto another:

1. Scientists first use "restriction enzymes" to snip out the gene for insulin from human DNA.
2. Then plasmids, a type of genetic material, are taken from bacteria cells. These small rings of DNA are not part of the normal bacteria chromosome, but can make the proteins needed by the bacteria. Plasmids can pass readily from bacteria to other cells, even those from species far apart on the evolutionary scale. This makes them ideal "vectors", think of little Trojan Horses which infiltrate a cell carrying a hidden payload.
3. The plasmid is extracted from a bacteria cell. Then the ring is cut at one point. The two ends are joined together again with the foreign gene, say, the human gene for making insulin,which is now part of the ring.
4. The modified plasmids are re-introduced into an E. coli cell. They can reproduce quickly, so the cell will soon have many plasmids carrying the foreign gene. The bacteria is now a transgenic organism, meaning that it has genes which have been transferred from a different species.
5. Once inside, the plasmids then start making insulin in the cell using the Trojan gene. When bacteria reproduce by dividing into two, the two daughter cells also carry the altered plasmids and so they can produce insulin.

The E. coli doubles its population every 20 minutes, and can quickly churn out a sizeable volume of the hormone.

This is harvested and purified.

Apart from insulin, the human growth hormone, produced in the pituary gland, has also been produced this way.

ANOTHER method for introducing foreign genes into a cell has resulted in goats with milk that contains spider's silk. Here scientists, use extremely small syringes to inject the spider gene for making web silk into the DNA of a fertilised goat egg.

Scientists have also used this method to get pigs to produce the human Protein C, which makes blood clot and is used for treating haemophiliacs. They are able to harvest one gram of Protein C from each litre of milk from a pig. The milk has 200 times the protein found in human-blood plasma.

 

Let there be light	Spider silk in your cuppa	Super rice
TALK about a luminescent addition to your aquarium: there are some fish that - get this - glow. This is one of the breakthroughs researchers made at the National University of Singapore. They injected a jellyfish gene that makes a green fluorescent protein into fish embryos. The ability to glow under ultraviolet light then becomes part of the basic genetic make-up of the fish, and will be passed on to the next generation. These fish are not in shops yet - scientists are still working on the little critters so they can glow in other colours, too. The same fluorescent protein also made news when a glowing bunny appeared on the scene, a creation of American artist Eduardo Kac. The rabbit, Alba, glows when you expose it to blue light. Mr Kac says that Alba was meant to encourage social discussion about the impact of genetic engineering.	Fancy some spider silk in your cuppa of goat's milk? Canadian scientists are happy to oblige: they have injected a spider gene into goat DNA. The gene is activated during lactation and one goat can produce five grams of silk protein per litre. The protein will be extracted from the milk to produce fibres - called BioSteel because, like spider webs, they are extraordinarily strong. Possible uses include lighter but stronger bullet-proof vests; biodegradable yet hardy sutures; and tougher aerospace components.	Transgenetic engineering is also happening in the plant world. Scientists have introduced into the rice genome the three genes for making beta-carotene, which we need for making Vitamin A. The genes come from different plants, including the daffodil. This is also the first time researchers have succeeded in transferring more than one gene at a time into a species. Polished rice usually lacks Vitamin A, and this deficiency is a major health problem in 26 countries. About a quarter of a million children in South-east Asia go blind each year because of it.

 

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