Researchers develop new cattle embryo screening methods

Scientists at the Monash Institute of Reproduction and Development are developing methods to screen cloned cattle embryos to identify embryos that show signs of abnormal imprinting -- a process that can lead to overgrown foetuses, placental problems and related disorders.

Imprinting is a phenomenon affecting about 60 genes in the embryo, where specific copies of the gene inherited from the mother or the father are switched on or off, allowing normal growth and development to occur. For some reason, cloned embryos often have abnormally imprinted genes, so that both copies of the gene are switched on or off, or the wrong copy is switched on.

Monash IRD researchers led by Dr Nancy Ruddock have examined eight imprinted genes in normal cow embryos that have been shown to play a potential role in early growth or implantation of the embryo into the uterus.

While the researchers are currently looking at mRNA expression levels, to see whether more or less of a particular gene product is being produced in the embryonic cells, they hope eventually to be able to use SNPs to identify whether the gene being expressed comes from maternally- or paternally-inherited DNA.

Ruddock hopes that comparisons between normal and cloned cow embryos will provide clues to why cloned embryos are prone to developmental abnormalities, and ultimately lead to a pre-implantation screen to determine whether a cloned embryo displays normal or abnormal imprinting of critical genes.

"If a norm for expression of these genes can be established, researchers will be able to screen embryos for abnormalities before they are implanted, giving a better success rate and improving animal welfare," she said.

Currently clone pregnancies are closely monitored for foetal overgrowth and other problems, with abnormal pregnancies terminated.

The research may also shed light on some human imprinting disorders, including Beckwith-Weidermann Syndrome and Angelman Syndrome.

Dr Paul Donelly, CEO of the Dairy CRC, which funded the research, said the research would greatly assist in the understanding of embryo development, and would aid the implementation of advanced breeding technologies.

The research is to be published in the April issue of the journal Biology of Reproduction.