Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Emily Singer

A View from Emily Singer

Animal Eggs No Good for Human Cloning

Only human eggs can reprogram human DNA.

  • February 2, 2009

A shortage of human eggs has been the major impediment to human cloning, so scientists have been trying to use animal eggs instead, a controversial approach that has raised fears of human-animal hybrids. Now new research suggests that using animal eggs as surrogates won’t be successful.

The image shows the development of a human-bovine
cloned embryo (top) and a human-rabbit cloned
embryo (bottom).
Credit: CLONING AND STEM CELLS, 2009
Mary Ann Liebert Inc.

In therapeutic cloning (or somatic cell nuclear transfer), scientists transplant DNA from an adult skin cell into an egg that has had its DNA removed. Unknown factors in the egg reprogram the adult DNA to resemble embryonic DNA, and, in theory, the cell begins to develop like a normal embryo. Scientists would like to create stem cells from cloned human embryos, both for research and potentially for therapy: the cells would be genetically matched to their human donors and thus could be transplanted without fear of rejection. But no one has yet accomplished this with human cells and eggs.

The creation of human-animal hybrids has been a subject of great debate in the United Kingdom, where scientists won permission to use rabbit and cow eggs in human cloning experiments in 2007. (This Q&A with Ian Wilmut, the biologist who spearheaded the cloning of the now renowned sheep Dolly, explores the controversy.) Similar research involving rabbit eggs has taken place in the United States, but with little government regulation here, there has been much less public debate.

A paper published today in Cloning and Stem Cells could make the debate moot. A comparison of gene expression in human cells transplanted into both human eggs and animal eggs suggests that animal eggs simply don’t have the power to reprogram human DNA. Here’s an extract from a press release issued by Advanced Cell Technology (ACT), which sponsored the research.

Although human-to-human clones (human clones) and human-to-animal clones (hybrids) appear similar, the pattern of reprogramming of the donor human cell is dramatically different. This study … shows for the first time that the donor DNA in the cloned human embryos is extensively reprogrammed through extensive up-regulation (“turning on” of genes) with similar expression patterns to normal human embryos. Nearly all of the key differentially-expressed genes were activated in the human clones. In distinct contrast, the majority of these genes were down-regulated or silenced in the human-animal hybrids.

Wilmut, who edits the journal, said in a statement, “This very important paper suggests that livestock oocytes are extremely unlikely to be suitable as recipients for use in human nuclear transfer. This is very disappointing because it would mean that production of patient-specific stem cells by this means would be impracticable.”

In the last year, scientists have been experimenting with a new method of reprogramming, which skips the egg altogether and instead uses several genetic factors to directly modify DNA. The ACT researchers also examined expression of these key genes and found that they were activated in both normal and cloned human embryos but not in the human-animal hybrids. “The human-animal hybrids showed no difference or a down-regulation of these critical pluripotency genes–effectively silencing them–thus making the generation of stem cells impossible. Without appropriate reprogramming, these data call into question the potential use of animal-egg sources to generate patient-specific stem cells,” said Robert Lanza, chief scientific officer at ACT, in an e-mail.

Some say that the characterization of reprogramming in human clones is the most interesting aspect of the research. According to an article in the Scientist,

The gene expression profiles now “lay the foundation” for other detailed molecular analyses of human-human clones with an eye toward isolating embryonic stem cells, said [Keith Latham, a developmental biologist at Temple University School of Medicine, in Philadelphia, who was not involved in the research]. [Justin St. John of Warwick University] agreed that the paper’s most important finding was the detailed characterization of human-human embryos, not the limited human-animal hybrid data. “That in and of itself is a success,” he said. “I’m not sure why they weren’t selling that point more … They seem to [be] spinning a negative result instead of spinning [a] positive result.”

AI is here.
Own what happens next at EmTech Digital 2019.

Register now
More from Rewriting Life

Reprogramming our bodies to make us healthier.

Want more award-winning journalism? Subscribe and become an Insider.
  • Insider Plus {! insider.prices.plus !}* Best Value

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

  • Insider Basic {! insider.prices.basic !}*

    {! insider.display.menuOptionsLabel !}

    Six issues of our award winning print magazine, unlimited online access plus The Download with the top tech stories delivered daily to your inbox.

    See details+

    Print Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

  • Insider Online Only {! insider.prices.online !}*

    {! insider.display.menuOptionsLabel !}

    Unlimited online access including articles and video, plus The Download with the top tech stories delivered daily to your inbox.

    See details+

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.