The disgraced group of Korean researchers under Hwang Woo-Suk, who published falsified embryonic stem cell research (most notably the retracted article from Science back in 2004), did achieve a genuine breakthrough, a newly conducted investigation on Korean group’s stem cell line shows. Scientists from the Children’s Hospital Boston, who analyzed Korean cells’ genetic makeup, believe that Hwang Woo-Suk et al. created the first known parthenogenetic embryonic stem cell line. Parthenogenesis refers to the process in which an embryo cell contains genetic material only from a donor egg.
The press office from Children’s Hospital Boston explains how the research was conducted by Kitai Kim, PhD, and George Q. Daley, MD, PhD.:
An initial investigation of the Korean group’s first embryonic stem cell line suggested it might be parthenogenetic in origin, but the analysis was inconclusive, and the cells’ origin, until now, had never been fully explained in a peer-reviewed journal.
Kim, Daley and collaborators used sophisticated genetic techniques to compare mouse embryonic stem cells derived from different sources: from embryos produced by natural fertilization; from embryos produced by parthenogenesis (through artificial activation of unfertilized eggs); and from embryos created through somatic cell nuclear transfer (replacing the nucleus of an egg with the nucleus from a cell in the body). They also tested three human embryonic stem cells isolated from fertilized embryos as well as the Korean line of human cells claimed to have been created through nuclear transfer.
They discovered that parthenogenetic embryonic stem cells have a distinct genetic signature that reflects their biological origins. All cells typically contain paired sets of chromosomes, one inherited from the mother and the other from the father. During the process of parthenogenesis, one set of chromosomes is duplicated, resulting in both chromosomes of the pair being of one parental type or the other (a pattern called homozygosity, which has reduced genetic diversity). Kim and Daley showed previously that because chromosomes often exchange genetic material early in the process of cell division that creates the egg (meiosis), the duplicated chromosomes are not actually identical, but have places where the genes differ between members of the pair (called heterozygosity). In embryonic stem cells of parthenogenetic origin, this occurs especially toward the ends of the chromosomes, which are more likely to exchange genetic material, rather than the middle. In contrast, embryonic stem cells created through nuclear transfer show a consistent pattern of variation through all regions of the chromosome — thus making them easily distinguishable from parthenogenetic cells.
The Korean cell line displays a genetic pattern that is clearly consistent with a parthenogenetic origin, Kim and Daley now show.
Because mistakes during nuclear transfer can result in parthenogenetic cells, Daley believes that the Hwang group generated parthenogenetic stem cells by accident, and didn’t have the tools to conclusively determine what they had created. The first isolation of parthenogenetic stem cells from humans would have been an important contribution, but the Hwang group’s attempt to pass off the cells as made by nuclear transfer was instead “a woeful case of misconduct,” he says.
Press release: Discredited Korean stem cells’ true origins revealed …