Template plasmid integration in germline genome-edited cattle

Scientist at the U.S. Food and Drug Administration (FDA) evaluated whole genome sequencing data of cattle that have been genetically modified so that they do not grow horns (polled). The cattle were originally modified with TALENs and the polled property was introduced into the cattle genome using a SDN-2/3 approach (original publication: Carlson, DF et al. Production of hornless dairy cattle from genome-edited cell lines. Nat Biotechnol 34, 479-481 (2016)). These genome-edited cattle do not form horns. The FDA’s study showed that not only the desired gene sequence, but also DNA sequences of genetically modified bacteria are integrated in the genome, which were used as vectors during the genetic modification process, and the template DNA used during the genome editing. In the cattle genome there are, among other things, complete DNA sequences that give bacteria resistance to certain antibiotics, which are important properties used for developing GMOs. The effects of the additionally inserted DNA sequences on the health of the animals and whether the genes are biologically active has not been investigated. The importance of this work is that the unintended DNA insertions were not discovered by the developers who claimed the cows were free from forgein DNA, but by the US FDA.