EXPRESSION OF RETINA-SPECIFIC GENES BY MOUSE RETINOBLASTOMA CELLS

Purpose. Two cell lines derived from ocular tumors of a transgenic mou se 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 comp ared these two lines with the normal adult mouse eye by analysis of th e expression of five photoreceptor cell-specific proteins: IRBP, opsin , rod- and cone-specific transducins, and S-antigen. The authors sough t to determine which of these proteins was expressed qualitatively and to examine semi-quantitatively for changes in the levels of expressio n in the cell lines. Method. Western blot analysis was used to detect photoreceptor-specific intracellular or secreted proteins. Total RNA w as prepared from cultured cells or from mouse adult whole eye. Specifi c messenger levels in total RNA were determined either by northern hyb ridization analysis or by a semiquantitative polymerase chain reaction (PCR), coupled to complementary DNA (cDNA) substrates prepared from t otal RNA. Results. IRBP was present in the retinoblastoma cell lines a nd secreted into the medium. Neither S-antigen nor opsin were detectab le by immunoblotting. IRBP and cone transducin mRNA were present in bo th cell lines. In contrast, opsin, rod transducin, and S-Antigen mRNAs were not detectable by PCR. p-actin was present in the mRNA populatio ns of whole eye and retinoblastoma. SV40 large T antigen mRNA was pres ent only in retinoblastoma cells. Conclusions. IRBP and cone transduci n expression in mouse retinoblastoma cells is independent of signaling provided directly or indirectly through large T antigen or Rb-105 reg ulatory cascades. The pattern of photoreceptor-specific gene expressio n is similar to that seen in human retinoblastoma cell lines. These mu rine-derived cell lines may be useful as a tool to study IRBP and cone transducin expression in vitro and to determine early retinoblast exp ression patterns in the mouse.