STORRS, Conn. -- University of Connecticut scientists and Japanese colleagues who produced six genetically identical calves using cells taken from the ear of a prize bull in Japan, have announced that they cultured the cells for up to 3 months in vitro before using them for cloning.
In the rapidly evolving field of cloning technology, it has been believed that long-term culture of donor cells would compromise (if possible at all) their efficiency for cloning. But the UConn scientists say that long-term culture of donor cells may do just the opposite and also may make it possible to manipulate genetic modifications in the donor cells prior to cloning.
Their findings could have enormous implications in the cattle industry and in the future applications of cloning technology in biomedical research.
A paper describing the cloning technique used to produce the six calves will appear in the January 4th issue of the journal "Proceedings of the National Academy of Sciences." Dr. Xiangzhong (Jerry) Yang, head of the University of Connecticut's Transgenic Animal Facility and corresponding author of the article, says the researchers were surprised to find that donor-cells of long-term culture were capable to support embryo development and production of offspring.
"These findings are novel and unexpected," Yang acknowledged. "We have produced normal cloned calves from adult somatic cells after 2- or 3-months of continuous culture in vitro. In fact, we observed higher developmental rates for embryos derived from donor cells after long-term culture than those after short-term culture. The significance of this research should set the stage for future targeted gene manipulations of the donor cells prior to cloning."
The research is the result of a collaboration between the laboratories of Dr. Chikara Kubota of the Kogashima Cattle Breeding Development Institute in Japan and Dr. Yang's Animal Transgenic Facility at UConn.
In Japan, scientists hope to use cloning technology to improve the breeding of beef cattle to obtain animals with higher quality meat. While technology exists that allows scientists to alter the site-specific genetic makeup in mice, it is dependent on the manipulation of mouse embryonic stem (ES) cells which are not available in other species.
However, animal cloning using cultured somatic cells (cells other than reproductive cells), offers the possibility of targeted genetic manipulations as those performed in mice, but only if those somatic cells remain competent for cloning after prolonged culture.
"Long-term culture of somatic cells is essential for the possible targeted genetic manipulations of donor cells to create targeted genetically altered cells, tissues, organs and animals via cloning," explains Yang. "Live clones have been obtained from adult somatic cells in sheep, mice and cows, however these clones all came from donor cells after short in vitro culture which did not allow targeted gene manipulations."
Another related issue about cloning animals surfaced recently after a study questioned whether Dolly, the cloned sheep, was healthy as the DNA genetic material she was copied from is aging at the rate of the older sheep from which she was cloned.
Thus Yang and Kubota's research was conducted to test the cloning competence of somatic cells obtained from aged donor animals, particularly after those "aged" donor somatic cells were subjected to long-term cultures. These combinations would provide a very important model for studying the aging process.
The six cloned calves they produced came from the skin cells of a genetically elite, aged (17-year-old) Japanese Black cattle bull named "Kamitakafuku." Famous in Japan for their superior meat quality, Kamitakafuku has produced nearly 160,000 offspring.
In December 1997, Yang and Kubota (who recently was admitted to UConn as a doctoral student to study under Yang), collected skin cells from the ear of Kamitakafuku. These cells were then cultivated in a culture containing few nutrients "starving" the cells so they stopped dividing before they are used for cloning.
The researchers then transferred the nuclei carrying genetic information from the cultivated cells after 2 months, and placed them in unfertilized eggs whose nuclei had been taken out. The eggs were then implanted in the wombs of surrogate cows. The process was repeated with another set of cells after 3 months in vitro.
Four calves were born in December 1998 from cells cultured for two months (two of these calves are still alive); and two more cloned calves were born in February 1999 from three months culture.
The four surviving cloned bulls are named as Kamitakafuku-1,-2,-3 and -4 in Japanese. Their American names are Tommy, Andy, Timothy and Anthony, for TATA, or the name for the genetic control region in their DNA. These clones are now 10 months (Timothy and Anthony) and 1-year-old (Tommy and Andy), and appear normal as compared to their conventionally reproduced peers.
"Our research shows that cells of aged animals remain competent for cloning, and prolonged culture does not affect the cloning competence of adult somatic donor cells," said Yang. "And cloning whole animals with somatic cells as parents offer the possibility of targeted genetic manipulations in vitro."
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