Detection of the Integrated Feline Leukemia Viruses in a Cat Lymphoid Tumor Cell Line by Fluorescence In Situ Hybridization

Feline leukemia virus (FeLV) is a type-C retrovirus associated with lymphoid and hematopoietic malignancies in cats. The FeLV-induced tumors are thought to be caused, at least in part, by somatically acquired insertional mutagenesis in which the integrated provirus may activate a proto-oncogene or disrupt a tumor suppressor gene. This study was undertaken to enumerate and map the acquired proviral insertions in the genome of a feline thymic lymphoma cell line (FT-1) infected with FeLV. Fluorescence in situ hybridization (FISH) combined with tyramide signal amplification was applied on the chromosome specimen of FT-1 cells and normal cat lymphocytes, with an entire FeLV-A genome used as a probe. Specific hybridization signals were detected from only the metaphases of the FT-1 cells, not from those of normal cat lymphocytes. Statistically based on the Poisson's distribution, at least six loci of chromosomal regions, A2p23-p22, B2p15-p14, B4p15-p14, D4q23-q24, E1p14-p13, and E2p13-p12, appeared to be positive for FeLV integration. Consistently, Southern blot hybridization analysis using an FeLV LTR-U3 probe specific for exogenous FeLV showed the integration of at least six FeLV proviral genomes in FT-1 cells. The cytogenetic technique employed here will provide valuable molecular tags to reveal unidentified tumor-associated genes in FeLV-associated tumor cells.