Survival after transfer of “sexed” mouse embryos exposed to H-Y antisera

Abstract

Metallothioneins (MTs) are small, cysteine-rich, metal-binding proteins found in most eukaryotes. We have isolated and characterized the mouse MT-I gene and have shown that this gene is transcriptionally regulated by heavy metals in vivo and in most cultured cells. To define the mechanisms and sequences responsible for transcriptional regulation, we have constructed vectors that include the MT-I gene along with a selectable marker gene. When these vectors are transfected into mouse or human cells the MT-I gene is transcriptionally regulated by cadmium. S1 mapping reveals that the 5’ end of the mRNA is the same as that originating from endogenous MT-I genes. The promoter and regulatory region of the MT-I gene has also been fused to the structural gene of herpes virus thymidine kinase resulting in a vector (pMK) in which thymidine kinase expression is controlled by cadmium when it is injected into mouse eggs. A minimum of 90 bp of mouse sequence 5’ of the mRNA cap site is required for cadmium regulation of thymidine kinase expression. Mouse eggs injected with pMK have been reimplanted into the oviducts of pseudopregnant mice. Several of the resulting mice express a high level of herpes thymidine kinase in the liver in response to cadmium. DNA analysis reveals multiple copies of the plasmid which are inherited as though they are integrated into a single chromosome. Some offspring of these mice also express viral thymidine kinase indicating that functional fusion plasmids can be stably incorporated into the germ line.