Human mini-chromosomes in mouse embryonal stem cells

We have introduced human mini-chromosomes of 4 Mb and approximately 15 Mbin size into mouse embryonal stem cells. Although these human mini-chromosomes are stable in hamster and chicken cells, they re-arrange orsegregate aberrantly in the embryonal stem cells and are rapidly lost inthe absence of selection. However, one of the mini-chromosomes re-arranged, acquired mouse centromeric sequences and was then stablymaintained for at least 60 population doublings in culture. This mini-chromosome, which is 4 Mb in size, is a candidate for a mouse germ linechromosome vector.