Tissue specific high level expression of a full length human endogenous retrovirus genome transgene, HERV-R, under control of its own promoter in rats.

Human endogenous retrovirus-R (HERV-R) is one of a full length HERV with a long open reading frame in the env region. The env transcripts are expressed in various human tissues. To investigate the biological role of HERV-R in vivo, we established two lines of transgenic rats carrying a full sequence of HERV-R under control of its own long terminal repeat (LTR) promoter. One line with tandem integration of multiple copies of the transgene expressed HERV-R mRNA in various organs with different expression levels and relatively higher in Harderian and submandibular salivary glands. In another line, the transgene was integrated as a single copy in a haploid and the expression was detected only in Harderian and submandibular salivary glands. In the placenta, one of the tissues with high levels of the HERV-R expression in humans, the transcription was evident starting the 12th day after gestation. A rabbit antiserum against synthetic peptides corresponding with the HERV-R env gene sequence led to detection of an 85 kDa product as a glycoprotein in the Harderian glands. While no pathological significance was observed in either line, the transgenic rat may prove to be a suitable model for analyzing the role of HERV-R function in vivo.