LIFE AFTER DOLLY
Dolly was the world's 1st mammal to be cloned from the cells of an adult animal, & since her birth in 1997 this cloning technology has seen a meteoric rise.
In July '97 Roslin Institute announced the birth of Molly & Polly. These lambs were cloned by the same technique as Dolly, except they used cells from the foetus of a Poll Dorset sheep (easier to clone than adult cells) that carried a human gene in their DNA. The researchers inserted 3 genes into the foetal sheep cells: 1 gene coded for Factor IX, another linked Factor IX to milk production & the 3rd conferred resistance to the antibiotic neomycin. Factor IX is an important blood-clotting protein used to treat haemophiliacs & the aim was to create ewes whose milk would contain this protein, to give a cheaper source with less risk of infection for these patients. When the foetal cells were exposed to neomycin all the cells that did not contain these inserted genes died. After fusion with enucleated eggs from Scottish Blackface ewes & culturing, 62 transgenic embryos were implanted into surrogate mothers. Six lambs were born live, 3 of which correctly carried the genes for Factor IX & 2 of which lived - Molly & Polly.
In January 1998 2 transgenic Holstein calves - George & Charlie - were born, created by J Robl at University of Massachusetts. His team used a similar technique to Roslin, giving the calves the DNA for an antibiotic resistance gene & a marker gene. Researchers are now engineering transgenic cows that can express serum albumin in their milk. This protein is used in patients who have lost a lot of blood eg those with severe burns. Cows produce more milk than sheep (about 80 kg/year) & 50 cows could make as much serum albumin as is currently pooled world-wide from human plasma per year at a fraction of the cost. Since then N First of University of Wisconsin has fused enucleated cow eggs with ear cells from 5 different mammals - sheep, pigs, rats & primates. This finding may lead to cows being used to host many different transgenic mammalian species. It appears some chemical signal in the cow egg reset the developmental clock of the ear cells returning them to an early developmental stage - however, the embryos did not survive implantation (it appears that the placenta fails to develop or function normally in many cases).
Here in New Zealand, research into cloning has been taking place at AgResearch at Ruakura in Hamilton. Their 1st calf, born in Feb'98, was 2nd in the world cloned from embryo cells. In 1998 Elsie & 4 other calves were born, all cloned from Lady - the sole survivor of the Enderby Island cattle, a rare breed of cattle that eat seaweed. It was interesting to note that all of these animals have different coat markings, despite being genetically identical & female. A bull, Derby, was formed by in vitro fertilisation of an egg from Lady using frozen sperm from dead Enderby Island bulls. Researchers hope to introduce new genes into the herd using the frozen sperm & eggs from the clones. In Oct '98 10 heifer calves were born, cloned by somatic cell nuclear transfer from a single adult, a high-performing Freisian dairy cow. These researchers are currently proposing to create transgenic cows to make a drug for multiple sclerosis. Scottish researchers in '98 won approval from ERMA to breed 10,000 transgenic sheep on a central North Island farm. These sheep will make a-1-antitypson in their milk to provide relief to sufferers of cystic fibrosis & congenital emphysema.
In March 2000 the 1st clones of pigs were bred - a milestone in the science of xenotransplantation as there is less risk of passing diseases from pigs to humans than, say, primates. Cloning also provides ways of genetically engineering these donors of organs (liver, kidney, heart) to be compatible with the human immune system.
QUESTIONS:
1. How do researchers select those cells that have the inserted gene from those that don't?
2. Why would foetal cells be easier to clone from than adult cells?
3. A. Why can't George & Charlie make milk?
B. What was the point of creating George & Charlie if they can't make milk?
C. What do you think a marker gene is?
D. What term describes animals that carry & express a foreign gene?
4. What is somatic cell nuclear transfer?
5. Why did the researchers need to create Derby?
6. What is xenotransplantation?
7. List 4 justifiable uses of cloning.