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A step forward for embryo culture.

A Step Forward for Embryo Culture

Sheep and cattle embryos can be kept alive and growing outside the mother's womb for up to 6 days by using tissue-cultured oviduct cells for nourishment.

The technique, called embryo co-culture, was originally developed by ARS scientists for sheep. "This allows us to make sure that only embryos that survive the manipulations of genetic engineering will be implanted into surrogate mothers," says animal physiologist Caird E. Rexroad, Jr., of Beltsville, Maryland.

In practice, single-celled embryos that have had a gene inserted are placed in cultures of cells from a sheep's oviduct. Scientists speculate that certain nutrients from the cultured cells keep the embryos alive and developing.

"So far, we've had a 30-percent success rate of implanting embryos that have been cultured for 3 days in surrogate ewes.

"Embryos cultured for 6 days that are in the blastocyst or hollow ball stage of development - the best phase for implantation - have a 20-percent chance of surviving. We work exclusively with sheep, but other laboratories have had similar results with cattle embryos," says Rexroad.

"Microscopic examination of the cultured embryos reveal whether they are developing properly. For example, an embryo cultured for 3 days should have more than eight cells; any fewer shows development is not proceeding normally," says biologist Anne M. Powell, a colleague of Rexroad on the research.

"Other, more sophisticated techniques can be used in conjunction with co-culture techniques to see if the genes implanted into the embryo have been incorporated into its genetic material," says Powell.

Alternative methods, such as placing gene-implanted cattle embryos in rabbits for 5 days and then removing them for implantation, have a greater chance of success but lack the advantage of the embryos' progress being visible. Culturing embryos in rabbits also requires more labor, and the animals must be destroyed to recover the embryos.

"Co-culture of cattle embryos is not yet ready to replace short-term transfer of genetically manipulated embryos into rabbit oviducts. But its perfection would be a boon to genetic engineers," says Rexroad.
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Author:Mazzola, Vince
Publication:Agricultural Research
Date:Jul 1, 1991
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