Expression of mRNA in monolayer cells transfected with a series of recombinant DNA was demonstrated by in situ hybridization with biotin- or 32P-labelled probes. Neomycin resistant mRNA stably expressed in pSV2neo transformed cells was positively stained in the cytoplasm of the cells by in situ hybridization with a biotinylated probe. A molecularly cloned provirus genome of a retrovirus produced in a human lymphoblastoid cell line was first introduced in canine fetal thymus cells, a host cell for the virus, and then the transient expressions of viral antigen and RNA were detected in several percent of the transfected cells by immunoperoxidase staining and in situ hybridization with biotin- or 32P-labelled probe. These results indicate that in situ hybridization is an useful method for detecting the expression of the gene introduced into mammalian cells.
