The G-proteins are a family of heterotrimeric guanine nucleotide-binding proteins that play important roles in signal transduction and whose expression is regulated in a tissue-specific manner. Here we have surveyed the expression of G-protein α-subunits in mouse pancreatic islets. Degenerate oligonucleotide primers corresponding to conserved primary sequences in known Gα-subunits were used in a reverse transcriptase-polymerase chain reaction, and the amplified complementary DNA (cDNA) fragments were subcloned and sequenced. Over 100 clones were analyzed, from which we determined that islet cells express at least seven G α-subunits: G8 α, Gi1α or Gi3α, Gi2α, G11α, G14α, Gzα, and Gt2α (cone transducin). In particular, the identification of Gzα and Gt2α was of interest in that previous studies had indicated that the expression of Gzα was restricted mainly to the brain, retina, and adrenal gland, whereas Gt2α was expressed predominantly in retinal cone photoreceptors. By Western blot analysis, we estimated that the amount of Gzα protein present in mouse islets was about 40% of that in retina. To further investigate the expression of Gt2α, mouse Gt2α cDNA was cloned from a retinal library and sequenced. The cDNA was used as a probe for Northern blot analysis, and the results confirmed that mouse islets contained a substantial level of Gt2α messenger RNA (mRNA), albeit less than that found in retina (∼ 5-fold lower). Gt2α mRNA was also shown to be present in a clonal mouse pancreatic α-cell line (α TC1-6) as well as in adrenal gland, pituitary, and a clonal mouse anterior pituitary cell line (AtT20). In situ hybridization revealed that Gt2α mRNA was expressed essentially throughout the islet, suggesting that it is normally expressed in the abundant islet beta-cells and possibly others. In situ analysis also showed that Gt2α mRNA expressed in the pituitary was limited to the intermediate and anterior lobes. We conclude that islet cells express multiple G-proteins, including several that are normally expressed at high levels in certain neuronal cells.
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