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Cloning, success rates

1% survival rate

One recently published paper indicates that the success rate for this process hasn't increased. Only 3 out of the 274 mouse embryos that were transferred to surrogate mothers survived to birth and only one survived into mouse adulthood."
(reported in a letter that Teruhiko Wakayama and Ryuzo Yanagimachi published in Nature Genetics 22 1999 pp 127-28)

Above was qutoed by Pete Moore in Babel's Shadow, pg 119

Increased survival with egg handling and maturing device.

24th May 2001, New Scientist reports, on the development of a device for maturing and nurturing eggs. David Beebe & Matthew Wheeler, embryologists at the University of Illinois at Urbana-Champaign, are doing this research and development work.
...This device has not been tested on human embryos

Tests at this stage have only been with mouse embryos. In the first 48 hours required to develop a mouse embryo to the blastocyst stage using traditional dish methods no embryos survived, but using the micro channelled elastomer slide 75% of the embryos survived to blastocyst, were implanted, and produced apparently healthy pups.

Faults in DNA methylation linked to deformed embryos.

It is known that many embryos produced by DNA transfer die. In fact only a few percent survive to term and some of those are born unhealthy.

Yong-Mahn Han of the Korea Research Institute of Bioscience and Biotechnology compared the methylations of sections of DNA  from cows embryos created by nuclear transfer, with DNA from embryos produced by normal IVF. As in natural embryos, those produced through IVF had lost their methylation by the time they became a blastocyst. In cloned embryo's some DNA had methylation areas at the blastocyst stage, and this in some cases did not clear up at all as the embryo developed.

Some researchers have suspected for some time that misplaced methylation was the serious problem in cloning - methylation helps to regulate the expression of the gene. Even lab culturing of embryos can disrupt methylation is not properly performed.

Han's team have identified a basic problem in cloned embryos "Its an important clue to why a lot of nuclear transfer embryos fail to develop." says Han.

Source.

New Scientist 2 June 2001, page 6 - article by Philip Cohen.

Cross refs.

 

clonefaults.htm