ISOFORM DIVERSITY OF THE INOSITOL TRISPHOSPHATE RECEPTOR IN CELL-TYPES OF MOUSE ORIGIN

Previous reports suggested the expression of four or live different In s(1,4,5)P-3 receptor [Ins(1,4,5)P(3)R] isoforms in mouse cells [Ross, Danoff, Schell, Snyder and Ullrich (1992) Proc. Natl. Acad. Sci. U.S.A . 89, 4265-4269; De Smedt, Missiaen, Parys, Bootman, Mertens, Van Den Bosch and Casteels (1994) J. Biol. Chem. 269, 21691-21698]. To explore this diversity further, we have isolated and sequenced partial clones of two Ins(1,4,5)P(3)R mRNAs from the mouse embryonic C(3)H10T1/2 cel l line. These clones showed between 94.2 and 94.9% sequence identity w ith the corresponding rat Ins(1,4,5)P(3)R-II and Ins(1,4,5)P(3)R-III i soforms. Based on these newly obtained sequences we have determined th e relative expression of the different Ins(1,4,5)P(3)R mRNAs in cultur ed cells and in animal tissues of mouse origin by a ratio reverse tran scriptase polymerase chain reaction (RT-PCR). Ins(1,4,5)P(3)R-I was ve ry prominent in brain and cerebellum and Ins(1,4,5)P(3)R-II in epithel ia such as kidney as well as in both cardiac and skeletal muscle. Ins( 1,4,5)P(3)R-III was highly expressed in all cultured cell types and in tissues with high cell turnover, e.g. testis. The prominent expressio n of Ins(1,4,5)P(3)R-I and Ins(1,4,5)P(3)R-III in A7r5 and C(3)H10T1/2 cells respectively was confirmed by immunoblot analysis and was compa tible with a lower threshold for Ins(1,4,5)P-3-induced Ca2+ release in the former cell type. Screening of a large number of mouse cell lines and tissues revealed the presence of Ins(1,4,5)P(3)R-I as well as of the Ins(1,4,5)P(3)R-II and Ins(1,4,5)P(3)R-III isoforms which were ide ntified in the present study, but in contrast with previous reports th ere was no evidence for more isoform diversity.