814 EXPRESSION OF A BACTERIAL GENE IN TRANSGENIC MICE

Abstract

We studied the tissue specificity and the developmental stage of expression of a bacterial gene, Ecogpt, following its introduction into the pronuclei of fertilized mouse oocytes by microinjection. Ecogpt, a gene not present in mammalian cells, codes for XGPRT (xanthine guanine pyrophosphoribosyl transferase), a purine salvage enzyme. We looked for both the presence of the gene and activity of the enzyme in tissues of embryos, fetuses and adults. The vectors used to introduce Ecogpt included the 69% fragment of bovine papilloma virus, pSV2-gpt, RD-114, and polyomavirus. Liveborn mice were assayed for the presence of the genes injected by Southern blot analysis of DNA extracted from tail tips. Where possible, we have assayed for enzyme activity by utilizing 14C-xanthine as a substrate for XGPRT in cell homogenates, and at all stages of development we have used an immunocytochemical procedure to detect XGPRT in tissue sections. To date, our results indicate that the BPV vector is embryotoxic since in those few animals born with BPV sequences, they are highly rearranged and there is no XGPRT activity detectable.