Increasing cloning efficiencies requires a better understanding of developmental abnormalities and gene expression in manipulated embryos

ABSTRACT Cloning is a platform technology that will be used to make major advances in agricultural sciences. The result is a more efficient method of making transgenic embryos, fetuses, and offspring. Enhanced production traits and disease resistance may be realized in animal agricultural by utilizing new assisted reproductive technologies. Cloning alone allows for the multiplication of genetically superior adult animals. This multiplication may reduce the need for expensive multiplier herds and allow producers to enhance their products through improved access to elite genetics, while producing a more consistent product that more closely meets and responds to consumer demands. The key development needed to move the technology to larger markets is a more efficient and consistent cloning method. Most problematic are the pregnancy losses and poorer offspring survivability associated with cloning. These losses and abnormalities seem to be at least associated with, but may be caused by, placental abnormalities. Currently, gene products are being isolated from fertilized and cloned embryos. A two-pronged approach is contemplated. One is to determine “normal” and “abnormal” gene expression patterns in embryos and use it as a diagnostic tool to preselect embryos before transfer into recipient animals. The other is to find candidate genes to modify in order to achieve normal development. These problems must be solved or largely negated before anyone can produce thousands of cloned animals. However, for transgenic applications, cloning needs are different. Producing a limited number of cloned transgenic animals is now more efficient than traditional microinjection procedures for production of transgenic animals. An additional benefit for transgenics through cloning is the ability to knock out genes.

Implications

Producing large numbers of cloned cattle still requires additional research. However, we are at a point where major improvements may be possible by combining cloning and transgenic technologies. Recently, gene-knockout cloned sheep were produced. Knockout cattle and pigs are not far behind. Specific gene inserts or conditional removals can now be contemplated. Cloning of cattle and pigs will present numerous opportunities to make genetic changes and multiply superior genotypes in the next few years.

Key Words: Gene Expression, Transgenics

© 2001, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2001. 79:E285-E289