Genome Instability in interspecific cell hybrids II. Aminopterin resistance and gene amplification in lines arising from fusions of cells from divergent mammalian species

Abstract

In order to investigate instances of genetic instability in divergent cell hybrids, we studied several RAT-resistant colonies recovered from fusions between HPRT or TK-deficient rodent cells and marsupial or monotreme cells. Most of these colonies proved to lack HPRT or TK activity and to have survived by acquiring resistance to aminopterin; such aminopterin-resistant lines were never recovered from parent cells subjected to HAT selection. Two of the aminopterin-resistant hybrids over-produced DHFR, and possessed either double minutes or an abnormally banded region, the cytological manifestations of gene amplification. Selection in higher aminopterin concentrations yielded a highly resistant line with 100X wild-type DHFR activity and a large homogeneously staining region. We suggest that interspecific cell hybrids are predisposed to gene amplification and may also show many other types of genetic and chromosomal instability, possibly thein vitro equivalent of the “genomic shock” phenomena described for interstrain or interspecies hybrids of plants or animals.