Abstract

A novel splice variant of RGS 9 was isolated from a rat hypothalamus, human retina, and a human kidney (Wilm’s) tumor. This variant, termed RGS 9L, differs from the retinal form (termed RGS 9S) identified previously in that it contains a 211- (rat) or 205- (human) amino acid proline-rich domain on the carboxyl terminus. The pattern of RGS 9 mRNA splicing was tissue specific, with striatum, hypothalamus- and nucleus accumbens expressing RGS 9L, whereas retina and pineal expressed RGS 9S almost exclusively. This pattern of mRNA splicing seemed to be highly conserved between human and rodents, suggesting cell-specific differences in the function of these variants. Transient expression of RGS 9L augmented basal and β-adrenergic receptor-stimulated adenylyl cyclase activity while suppressing dopamine D₂receptor-mediated inhibition. Furthermore, RGS 9L expression greatly accelerated the decay of dopamine D₂ receptor-induced GIRK current. These results indicate RGS 9L inhibits heterotrimeric G_i function in vivo, probably by acting as a GTPase-activating protein. The human RGS 9 gene was localized to chromosome 17 q23–24 by radiation hybrid and fluorescent in situ hybridization analyses. The RGS 9 gene is within a previously defined locus for retinitis pigmentosa (RP 17), a disease that has been linked to genes in the rhodopsin/transducin/cGMP signaling pathway.