ABSTRACT
Transgenic production efficiency could be increased and costs could be dramatically reduced if a means were available to identify transgenic preimplantation embryos prior to transfer into recipients. In an attempt to determine when microinjected DNA concatemerises we conducted a series of experiments. Only in asynchronously injected embryos was ligation between genes significantly reduced, indicating that intermolecular ligation is an efficient process in pronuclei and likely to occur before transgene integration. Understanding the mechanism of transgene integration could provide the insight needed to develop strategies for improving efficiency and lowering costs. Most studies have clearly demonstrated that DNA injected into either pronuclei of zygotes or nuclei of 2-cell embryos is detectable at least until the blastocyst stage of development. Because the studies were Polymerase Chain Reaction based, it was not possible to distinguish between integrated and unintegrated transgenes.
