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Journal of Virology, April 2007, p. 3816-3826, Vol. 81, No. 8
0022-538X/07/$08.00+0 doi:10.1128/JVI.02425-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Department of Molecular Microbiology and Immunology and The Vaccine and Gene Therapy Institute, Oregon Health and Science University, Portland, Oregon 97239,1 Department of Surgery, Oregon Health and Science University, Portland, Oregon 97239,2 Portland VA Medical Center, Portland, Oregon 97239,3 Department of Medical Microbiology, University Maastricht, Maastricht, The Netherlands4
Received 3 November 2006/ Accepted 8 January 2007
Rat cytomegalovirus (RCMV) is a ß-herpesvirus with a 230-kbp genome containing over 167 open reading frames (ORFs). RCMV gene expression is tightly regulated in cultured cells, occurring in three distinct kinetic classes (immediate early, early, and late). However, the extent of viral-gene expression in vivo and its relationship to the in vitro expression are unknown. In this study, we used RCMV-specific DNA microarrays to investigate the viral transcriptional profiles in cultured, RCMV-infected endothelial cells, fibroblasts, and aortic smooth muscle cells and to compare these profiles to those found in tissues from RCMV-infected rat heart transplant recipients. In cultured cells, RCMV expresses approximately 95% of the known viral ORFs with few differences between cell types. By contrast, in vivo viral-gene expression in tissues from rat heart allograft recipients is highly restricted. In the tissues studied, a total of 80 viral genes expressing levels twice above background (5,000 to 10,000 copies per µg total RNA) were detected. In each tissue type, there were a number of genes expressed exclusively in that tissue. Although viral mRNA and genomic DNA levels were lower in the spleen than in submandibular glands, the number of individual viral genes expressed was higher in the spleen (60 versus 41). This finding suggests that the number of viral genes expressed is specific to a given tissue and is not dependent upon the viral load or viral mRNA levels. Our results demonstrate that the profiles, as well as the amplitude, of viral-gene expression are tissue specific and are dramatically different from those in infected cultured cells, indicating that RCMV gene expression in vitro does not reflect viral-gene expression in vivo.
Published ahead of print on 24 January 2007.
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