Early postimplantation embryo lethality due to DNA rearrangements in a transgenic mouse strain

Insertional mutagenesis in a transgenic mouse strain (HUGH/3) was caused by integration of plasmid DNA containing the human growth hormone gene and pBR322 plasmid sequences. From this study, which includes another instance of mutagenesis, and from other reports, it is apparent that insertional mutagenesis occurs fairly frequently during DNA integration in the mouse egg and that it is not specific for the exogenous DNA employed. The mutation in HUGH/3 is recessive and results in death of embryos homozygous for the donor sequences shortly after implantation, at the egg cylinder stage on days 4-5 of gestation. Restriction mapping of the insert and of the flanking DNA regions indicates that integration must have involved a series of complex events. Approximately five copies of plasmid sequences are arrayed in tandem but are interrupted at least twice by mouse cellular sequences. In addition, the mouse flanking DNA shows extensive rearrangements, probably including a deletion of at least 10 kilobases. The rearrangements may reflect an initially unstable DNA structure followed by attainment of a more stable conformation.