Purpose: Two cell lines derived from ocular tumors of a transgenic mouse expressing the SV40 large T antigen have been established as models of human retinoblastoma. One line, TM, originated from a metastasis, and the other, TE, originated from the primary tumor. The authors compared these two lines with the normal adult mouse eye by analysis of the expression of five photoreceptor cell-specific proteins: IRBP, opsin, rod- and cone-specific transducins, and S-antigen. The authors sought to determine which of these proteins was expressed qualitatively and to examine semi-quantitatively for changes in the levels of expression in the cell lines.
Method: Western blot analysis was used to detect photoreceptor-specific intracellular or secreted proteins. Total RNA was prepared from cultured cells or from mouse adult whole eye. Specific messenger levels in total RNA were determined either by northern hybridization analysis or by a semi-quantitative polymerase chain reaction (PCR), coupled to complementary DNA (cDNA) substrates prepared from total RNA.
Results: IRBP was present in the retinoblastoma cell lines and secreted into the medium. Neither S-antigen nor opsin were detectable by immunoblotting. IRBP and cone transducin mRNA were present in both cell lines. In contrast, opsin, rod transducin, and S-Antigen mRNAs were not detectable by PCR. beta-actin was present in the mRNA populations of whole eye and retinoblastoma. SV40 large T antigen mRNA was present only in retinoblastoma cells.
Conclusions: IRBP and cone transducin expression in mouse retinoblastoma cells is independent of signaling provided directly or indirectly through large T antigen or Rb105 regulatory cascades. The pattern of photoreceptor-specific gene expression is similar to that seen in human retinoblastoma cell lines. These murine-derived cell lines may be useful as a tool to study IRBP and cone transducin expression in vitro and to determine early retinoblast expression patterns in the mouse.