METHYLATION OF COTTONTAIL RABBIT PAPILLOMAVIRUS DNA AND TISSUE-SPECIFIC EXPRESSION IN TRANSGENIC RABBITS

Transgenic rabbits carrying multiple copies of CRPV genomic DNA were d escribed previously (Peng et al, (1993) J. Virol. 67, 1698-1701). CRPV DNA was detectable in all tissues of the transgenic rabbits, however, the transcripts of CRPV genes only were found in skin and skin tumors . Tumor development was also restricted to skin. To study the mechanis m involving tissue-specific expression of CRPV genes in rabbits, cellu lar DNAs, isolated from different normal tissues and skin tumors, were digested with the two isoschizomeric restriction endonucleases MspI ( methylation resistant) and HpaII (methylation sensitive), respectively , and analyzed by Southern blot. CRPV DNA, especially its upstream reg ulatory region (URR), was extensively methylated in all normal tissues , but methylation was remarkably reduced in skin tumors. These data su ggest that extensive methylation of CRPV genome, especially in the URR , might be a factor in controlling its tissue-specific expression.