Patterns of HIV-1 mRNA expression in transgenic mice are tissue-dependent

To explore tissue-specific factors that may be important in HIV-1 transcriptional and post-transcriptional regulation, we examined a transgenic mouse model containing a mutant provirus deleted in the gag and pol region. The level of transgene expression was tissue-dependent. Skin, muscle, and tail consistently expressed the transgene abundantly; intestine, kidney, and thymus exhibited variable but generally low levels of expression; while liver expression was undetectable by Northern analysis. Individual mRNAs within the family of singly and multiply spliced messages were determined by reverse transcription (rt) of RNA samples from mouse tissues, polymerase chain reaction (PCR) amplification, and Southern hybridization with exon-specific probes. The exact percentage of Tat-coding mRNA that was multiply spliced was also determined by competitive rtPCR. When 2-, 4-, or 7-kb (full-length) mRNA species were calculated as a percentage of the total mRNA, two phenotypes of distribution were detected. Lymphoid tissue (thymus and spleen) and kidney had significantly greater amounts of unspliced message (P < 0.001) regardless of the level of expression. All other tissues expressed the multiply spliced messages encoding Tat, Rev, and Nef predominantly. Furthermore, utilization of the three major second exon splice acceptor sites for tat, rev, and nef was the same in transgenic mice as has been demonstrated in human cells but the splice acceptor site for the vpu/env was different in murine tissue. The marked tissue-dependent patterns of HIV mRNA expression suggest a potential mechanism for the organ-specific manifestations of AIDS.