Gene targeting from laboratory to livestock: current status and emerging concepts.

The development of methods for cell-mediated transgenesis, based on somatic cell nuclear transfer, provides a tremendous opportunity to shape the genetic make-up of livestock animals in a much more directed approach than traditional animal breeding and selection schemes. Progress in the site-directed modulation of livestock genomes is currently limited by the low efficiencies of gene targeting imposed by the low frequency of homologous recombination and limited proliferative capacity of primary somatic cells that are used to produce transgenic animals. Here we review the current state of the art in the field, discuss the crucial aspects of the methodology and provide an overview of emerging approaches to increase the efficiency of gene targeting in somatic cells.