TRANSGENIC CATTLE RESULTING FROM BIOPSIED EMBRYOS - EXPRESSION OF C-SKI IN A TRANSGENIC CALF

Producing transgenic cattle by microinjection of DNA into pronuclei ha s been inefficient and costly, in large part because of the cost of ma intaining numerous nontransgenic pregnancies to term. We designed a sy stem for early identification of transgenic embryos in which biopsies of embryos were assayed by polymerase chain reaction for presence of t he transgene before embryo transfer. A total of 2555 embryos were micr oinjected with one of two DNA constructs. Of the 533 embryos biopsied, 112 were judged to be potentially transgenic and were transferred non surgically to recipients, resulting in production of 29 putative trans genic fetuses. One fetus and one calf (7% of offspring) were subsequen tly shown to be definitively transgenic. The calf was transgenic for a chicken c-ski cDNA, and several months after birth developed dramatic muscular hypertrophy followed by muscle degeneration. This phenotype was associated with expression of high levels of mRNA from the transge ne.