PHOTORECEPTOR DEGENERATION INDUCED BY THE EXPRESSION OF SIMIAN VIRUS-40 LARGE TUMOR-ANTIGEN IN THE RETINA OF TRANSGENIC MICE

Expression of the viral oncogene encoding the simian virus 40 (SV40) large tumor antigen (T antigen) typically promotes tumorigenesis in mammalian cells. To generate transgenic mice that express T antigen in rod photoreceptors, a chimeric construct consisting of a mouse opsin promoter fragment fused to the coding region of SV40 T antigen was generated. Expression of T antigen in the transgenic retina began at early stages of postnatal development concomitant with expression of endogenous opsin. Instead of inducing hyperplasia or tumor formation, T-antigen expression caused a rapidly progressing photoreceptor degeneration. The degeneration was accompanied by sustained DNA synthesis in photoreceptor cells, as evidenced by incorporation of [H-3]thymidine and by the appearance of mitotic figures at postnatal day 10, a stage when nontransgenic photoreceptor cells are post-mitotic and quiescent. Although transgenic photoreceptor cells undergo S phase and enter mitosis, the consequences of T-antigen expression are not proliferation and tumorigenesis but proliferation and cell death.