Gprk2 Controls cAMP Levels in Drosophila Development

Abstract

G protein-coupled receptors mediate their biological responses through the generation of second messengers, such as cAMP. The down-regulation of their activity (desensitization) is carried out, in part, by the family of G protein-coupled receptor kinases, which phosphorylate activated receptors. The Gprk2 gene in Drosophila melanogaster is a putative member of this family. The GPRK2 protein is expressed most abundantly in the ovaries and in the mushroom bodies, the brain region that is implicated in learning and memory in insects. Many of the genes that are involved in learning in Drosophila are members of a cAMP-signaling pathway and are also expressed in the mushroom bodies. These observations suggest that the Gprk2 gene may be involved in a cAMP-mediated pathway. To investigate this possibility, we tested for a genetic interaction between Gprk2 and dunce (which encodes cAMP-specific phosphodiesterase). A mutant allele of Gprk2, called gprk2(6936), has decreased fertility as a result of reduced levels of egg laying and hatching, and developing egg chambers display defects in the formation of anterior structures. Similarly, many alleles of dunce are sterile, with an ovary phenotype that resembles gprk2(6936). Introduction of a single copy of a hypomorphic or null allele of dunce into the gprk2(6936) background suppressed all of these defects to a significant degree. Suppression was also observed when a single copy of gprk2(6936) was introduced into a dunce background. Like mutants of rutabaga (which encodes a calcium/calmodulin-dependent adenylate cyclase), gprk2(6936) has reduced levels of cAMP. Ovaries from gprk2(6936) females contain about one third of the normal amount of cAMP. In addition, in every mutant combination where fertility is increased, cAMP levels are closer to wild type levels. These results suggest that Gprk2 is functioning in a cAMP-signaling pathway and that the underlying basis of the interaction between Gprk2 and dunce is a normalization of cAMP levels.

Drosophila G-protein-coupled receptor kinase 2 regulates cAMP-dependent Hedgehog signaling

“…Extending the results of Lannutti et al (Lannutti et al, 2001), we find that the reduction of cAMP levels caused by loss of Gprk2 is a general effect, occurring not only in adult animals but during development and in cultured cells as well. Importantly, our results clearly implicate this cAMP misregulation in the impairment of Hh target gene expression.…”

“…Given the central role of Pka in Hh signaling, cAMP misregulation could have significant effects on target gene expression. Consistent with a role for Gprk2 in cAMP regulation, baseline ovarian cAMP levels were about threefold lower than normal in flies homozygous for a tissue-specific regulatory mutant allele of gprk2 (Lannutti and Schneider, 2001 del2 wandering third-instar larvae (Fig. 3A).…”

Vitellogenesis and Post-Vitellogenic Maturation of the Insect Ovarian Follicle

“…The signaling pathways, between the germline and the cells of the follicular epithelium that coordinate these processes, include the c-Jun-NH 2 -terminal kinase (JNK) pathway (Dequier et al, 2001;Dobens et al, 2001) and others that may involve GPCRs and cAMP signaling (Schneider and Spradling, 1997;Lannutti and Schneider, 2001;Pathirana et al, 2001). …”

Role of the Drosophila Non-Visual ß-Arrestin Kurtz in Hedgehog Signalling

“…The GRK family includes seven members in humans (GRK1-7) and two components in flies (Gprk1 and Gprk2). Gprk1 modulates the amplitude of the visual response, acting as a Rhodopsin kinase, whereas Gprk2 regulates the level of cAMP during Drosophila oogenesis [19]. In addition, Gprk2 and Gprk1 play a key role in the regulation of the Hedgehog (Hh) signal transduction pathway [20]–[21], where they seem to phosphorylate and activate the seven-pass transmembrane protein Smoothened (Smo) [22].…”