Six cloned calves have been created from cells cultured in vitro for up to three months, confirming previous work showing that relatively “old” cells can be used to clone whole animals.
The achievement confirms the possibility of being able to carry out targeted genetic manipulations in vitro—taking out specific genes and replacing them with other ones—because this requires prolonged culture of nuclear donor cells.
A research team working in Japan and the United States has reported the birth of six clones of a 17 year old Japanese Black Beef bull, using ear skin fibro-blast cells as nuclear donor cells.
These cells were used after up to three months of in vitro culture, representing 10 to 15 culture passages. The four surviving clones are now 7 to 9 months old and seem normal, with no apparent differences compared with their peers produced by natural reproduction, according to the research team, whose results are due to appear shortly in the Proceedings of the National Academy of Sciences.
Professor Jerry Yang, director of the Transgenic Animal Facility at the University of Connecticut, Storrs, and member of the research team, commented: “These data show that fibro-blasts of aged animals remain competent for cloning and prolonged culture does not affect the cloning competence of adult somatic donor cells.”
He said that the demonstration of genetic totipotency of cells after prolonged culture is pivotal to combining site specific genetic manipulations and cloning.
The research suggested that long term storage of cells might even have been beneficial. Higher developmental rates for embryos derived from later passages (10 and 15) compared with those embryos from an early passage (passage 5).
Other groups working on transgenic animal research welcomed the report but questioned how much was new.
Dr Harry Griffin, assistant director at the Roslin Institute, near Edinburgh, which published a report on the birth of the cloned sheep Dolly in 1997, pointed out that the Roslin group had published work in 1996 reporting the production of clones from embryo derived cells kept in vitro for 13 passages.
Figure.
(AP PHOTO/HO)
Four calves, cloned from cells cultured for several months, show that relatively “old” cells can be used for cloning