Germ line transmission of autonomous genetic elements in transgenic mouse strains.

Upon microinjection into fertilized mouse eggs of circular molecules of plasmid pPyLT1 carrying the gene encoding the large T protein of polyoma virus within bacterial vector sequences, autonomous circular plasmids were stably maintained in low copy numbers in transgenic strains. These plasmids could be rescued in E. coli by transfection. Integrated forms could be detected neither in somatic tissues, nor in spermatozoa. Efficiency of paternal or maternal transmission was close to 100%. The plasmids had lost or had extensively rearranged the polyoma sequences. In addition, they had acquired defined segments of genomic mouse DNA, which might be responsible for correct segregation of daughter copies at both mitosis and meiosis (centromeric function).