Germ line transmission of yeast artificial chromosomes in transgenic mice

Several groups have recently reported the successful generation of transgenic mice harbouring yeast artificial chromosomes (YACs). Different methodological approaches have been shown to produce similar results, namely, the faithful expression of the transgenes carried on YAC DNA. In this paper, we compare the reported techniques for obtaining transgenic mice carrying YACs using a 250-kb YAC bearing the mouse tyrosinase gene. These methods include: microinjection of gel-purified YAC DNA into pronuclei of fertilized mouse oocytes, yeast spheroblast fusion with embryonic stem (ES) cells and lipofection of YAC DNA into ES cells. Taken together, these reports show that the delivery of large genomic regions covering a gene of interest (such as those cloned in YAC vectors) is feasible, and will ensure appropriate temporal and spatial expression of the transgene at a level comparable to that of the endogenous counterpart.