Human cloning may be impossible

[Brian]

Studies: Human Cloning May Be Impossible
Thu Apr 10, 2:07 PM ET

By LAURAN NEERGAARD, AP Medical Writer

WASHINGTON - Cloning humans, or any other primates, may be impossible with today's techniques because of a fundamental molecular obstacle, say scientists trying to understand why attempts to clone monkeys have failed.



From the very first step, cloned primate cells don't divide properly, causing a helter-skelter mix of chromosomes too abnormal for pregnancy to even begin, University of Pittsburgh researchers reported Thursday in the journal Science.


"Most people in the cloning field will be surprised by this," said lead researcher Gerald Schatten. "This work demonstrates there's a pothole in the process. We now know the depth and breadth of the pothole, and we're designing strategies to get around" it.


Dozens of animal clones — including cows, pigs, mice, goats and a cat — have been born since Dolly the sheep became the first new being created from an adult cell in 1997. But it's still a very uncertain field: Many are stillborn and some survive only with severe defects.


A cult group claimed in December to have cloned a person, something never verified. A doctor who separately is pursuing human cloning has reported in an Internet journal preliminary data on an early-stage cloned human embryo, but with no chromosome information.


Cloning experts worry that attempting human cloning is dangerous not just because of all the barnyard clones with birth defects, but because attempts to clone monkeys — far closer genetically to people — using the Dolly technique so far have failed.


To clone, scientists harvest an unfertilized egg from a female donor, removing the genetic material and replacing it with new DNA from an adult cell of the animal to be cloned. An electric shock coaxes it into dividing. If all goes well, the egg grows into an embryo that can be implanted into a surrogate mother.


It took 277 attempts before Dolly was born. Schatten's group tried even longer to clone a rhesus monkey — 724 eggs that yielded only 33 embryos and not a single pregnancy.


For cells to properly divide, chromosomes must duplicate themselves and precisely line up along a zipper-like structure called a spindle. Once the chromosomes are in place, the spindle helps the cell pull apart into two. During human reproduction, if the chromosomes don't split properly, defects such as Down syndrome result, or the pregnancy fails.


Schatten wondered if chromosome abnormalities were behind failed monkey clonings. Indeed, inside cloned monkey cells, the Pittsburgh researchers discovered deformed spindles and chaotic chromosome numbers.


Why? Eggs harbor proteins that act as molecular motors that are key to spindle formation. In primates, those proteins are so tightly bound to the egg's DNA that cloning's first step of DNA removal pulls them out, too, dooming hope of later pregnancy, Schatten said.


In other mammals, enough spindle-forming proteins float in the egg's remaining fluid for reproduction to occur, he said.


The discovery is very important, said Dr. Duane Kraemer, a successful cloner of non-primates at Texas A&M University.


"The fact that they don't get pregnancies at all is suggestive that there is something different going on there than with other species," he said. "It points to a potential problem that may have to be solved before the next advance can be made."


It's not just bad news for reproductive cloning. It also means the related field of therapeutic cloning — using embryonic stem cells to grow customized tissues for medical treatment — may prove harder, too, Schatten said. However, if 95 percent of cells growing in a lab dish have abnormal chromosomes, the remaining good 5 percent could still be used, he added.


His lab is exploring a way to overcome the problem, by combining cloning with old-fashioned egg fertilization. The sperm-and-egg joining jump-starts spindle formation. Schatten then pulls out that sperm and egg DNA, leaving just the clone DNA in the now-growing monkey cells.


"The value of this for deriving embryonic stem cells is going to be very attractive," Schatten said.

[Ravey]

I'm against cloning..

[Tuesday Weld]

I am SO against cloning,I think it's sick.

[Chocoholic]

I'm also against cloning.

[Jem]

I don't think it's right to clone other living beings, whether they're human or animal. I can see therapeutic cloning being possible though. For example, if I remember right, I think the sheep that Dolly was created from was a dead sheep. Therefore, according to the aging process, the cells in the adult sheep should have been all old or mostly dead before Dolly was created, which would explain Dolly's short lifespan, since cloning is making an exact copy of cells, so theoretically, cloning dead or almost-dead cells would result in getting an exact copy of the almost-dead or dead cells of the being.

If an embryonic cell was cloned, not the human embryo itself, but just one of the cells taken from the baby, that could then be put back into the baby once a clone was produced of the cell, then having a young embryonic cell cloned, and cloning that same younbg cell over and over until a cluster is made, therapeutic cloning could be very possible.

[webuster]

Currently, I'm for cloning, not because I'm a New Age sadistic person, who thinks it's cool- but because it is in the name of science, I am however, against people cloning embryos, then having babies just to get parts for their real child to survive.

[Crimson and Clover]

i am also against cloning

[Mijada]

I don't agree with it either. I don't understand why they want to clone all these animals. People are always telling us to have our pets spayed and neutered because there are too many animals and then they want to go ahead and make more animals. I can understand why they made Dolly, just to see if it was possible, but why keep on doing it? I think human cloning is creepy. If they start doing that, I'd hate to see in 10 or 20 years all the problems that these cloned humans are going to have to deal with.

[*Melissa*]

I hope it is impossible. I hate the very idea of cloning, whether it's human, non-human, or plant-life.

You'd think they could find better things to spend our money on... like finding a cure for the various types of cancers.

[-*Leah*-]

Good ! I hope that its impossible because I think that its very wrong, and I am totally against cloning.