Gene silencing in mammalian cells.

Abstract

Gametic Imprinting is the unequal expression of genes from the male and female alleles that results in parental dependant traits. We report here of an unusual Pgk-1,2-lacZ transgenic line that is irreversibly inactivated when passaged through the female germline. Inactivation of the transgene is correlated with methylation. HpaII sites within the lacZ region of the inactivated transgene are completely methylated, and treatment of mouse embryonic fibroblasts carrying inactivated transgenes with 5-aza-2-deoxycytidine results in reactivation. Additionally, we used P19 embryonal carcinoma cells to examine transgene inactivation, as cultured cells are more amenable to manipulation. Once again, methylation was correlated with transgene inactivation. Cells uniformly expressing the Pgk-1,2-lacZ transgene are also methylated to a slightly lesser degree suggesting that within transgene arrays, only a subset of transgenes are actively transcribed.