Molecular Cloning of a Lobster Gα_q Protein Expressed in Neurons of Olfactory Organ and Brain

Abstract

Abstract:We have isolated from an American lobster (Homarus americanus) olfactory organ cDNA library a clone, hGaq, with >80% identity to mammalian and arthropod Gaq sequences. In brain and olfactory organ, hGcsq mRNA was expressed predominantly in neurons, including virtually all the neuronal cell body clusters of the brain. Gaq protein was also expressed broadly, appearing on western blots as a single band of 46 kDa in brain, eyestalk, pereiopod, dactyl, tail muscle, olfactory organ, and aesthetasc hairs. These results suggest that hGaq plays a role in a wide variety of signal transduction events. Its presence in the olfactory aesthetasc hairs, which are almost pure preparations of the outer dendrites of the olfactory receptor neurons, the expression of a single hGcsq mRNA species (6 kb) in the olfactory organ, and the localization of hGaq mRNA predominantly in the olfactory receptor neurons of the olfactory organ strongly suggest that one function of hGaq is to mediate olfactory transduction. Key Words: Olfaction-G protein-Signal transduction -Crustaceans-Lobster. J. Neurochem. 68, 2248-2254 (1997).Olfactory transduction can be mediated by either the cyclic adenosine 3 '-monophosphate (cAMP) or the i nositol 1 ‚4,5-trisphosphate (InsP 3) pathways, with odorants activating both in most species (Ache, 1994;Dionne and Dubin, 1994). The roles such dual transduction pathways might play depend on whether they interact within individual olfactory receptor neurons (ORNs) or whether they are separated by odor sensitivity, odor concentration dependence, or exclusive expression patterns. In mammalian ciliary membrane preparations, there is a complete separation of the odor sensitivity of the cAMP and InsP1 pathways (Boekhoff et al., 1990; Breer and Boekhoff, 1991), although ORNs in culture may show activation of both pathways by an odorant (Ronnett et al., 1991). However, the total absence of odor responses in mice lacking functional olfactory cyclic nucleotide-gated channels suggests that the (lnsP3) pathway is not a primary transduction pathway (Brunet et al., 1996). Although these conflicting results raise doubts about the role of InsP3 in olfactory transduction in mammals, results from other species are more definitive. In catfish, both pathways are activated by odorants (Huque and Bruch, 1986;Bruch and Teeter, 1990) and conductances activated by each appear to occur in virtually all catfish ORNs (Miyamoto et al., 1992). This suggests that both pathways can coexist in a single ORN. In lobster ORNs this coexistence was established in single-cell recordings of the summation of depolarizing receptor potentials caused by odor-evoked InsPproduction and hyperpolarizing receptor potentials caused by odorevoked cAMP production (McClintock and Ache, 1989b;Michel et al., 1991;Fadool and Ache, 1992;Boekhoff et al., 1994;Hatt and Ache, 1994;Michel and Ache, 1994). The discovery that virtually all odorants can cause depolarizations in one lobster ORN but hyperpolarizations in another supports the hypothesis that this interactio...

Immunolocalization of a Gαq protein to the chemosensory organs of Dipolydora quadrilobata (Polychaeta: Spionidae)

“…The results of immunolocalization experiments on D. quadrilobata agree with previous findings of Gαq localization to chemosensory structures and organs in other invertebrate species (Talluri et al 1995;McClintock et al 1997;Munger et al 2000;Mezler et al 2001;Jacquin-Joly et al 2002). Among the polychaetes, nuchal organs are typically considered to function in chemoreception based on histological, ultrastructural, and positional criteria (Storch and Schlötzer-Schrehardt 1988;Rhode 1990;Purschke 1997Purschke , 2005.…”

“…Insects appear to use only Gαq and Gαo/i for transducing chemical signals (Boekhoff et al 1990;Talluri et al 1995;Krieger and Breer 1999;Jacquin-Joly et al 2002). Overall, Gαq is one of the most commonly found G-proteins in chemosensory cells of aquatic invertebrates, and evidence also supports a role of Gαq in chemosensory signal transduction in marine invertebrates (Knol et al 1992;McClintock et al 1992McClintock et al , 1997Fadool et al 1995;Xu et al 1997;Mezler et al 2001). …”

“…f Gold labeling in gland cells (arrows). Bar 0.5 μm depolarization of the olfactory neuron (Hatt and Ache 1994;Fadool et al 1995;McClintock et al 1997;Munger et al 2000). Because the feeding palps of D. quadrilobata respond to chemical cues and contain putative chemosensory cells (Riordan and Lindsay 2002;Lindsay et al 2004), the identification of Gαq from feeding palps suggests that a G-protein-mediated chemosensory signal transduction pathway may be present in this polychaete.…”

“…Histological and activitydependent cell-labeling studies in D. quadrilobata suggest several types of palp cilia may be chemosensory (Lindsay et al 2004). Although the molecular mechanisms of chemoreception have not been well described in lophotrochozoan phyla such as the annelida, given the high degree of conservation for G-protein sequence and function among metazoan taxa examined to date (Quan and Forte 1990;Knol et al 1992;McClintock et al 1997;Xu et al 1997;Munger et al 2000;Jacquin-Joly et al 2002), we might reasonably expect that Gαq plays an important role in mediating chemosensory-based feeding behaviors in annelids. Consistent with this expectation, we report the identification of a putative chemosensory Gαq gene and describe its localization to sensory structures in the marine annelid D. quadrilobata (Polychaeta: Spionidae).…”

Characterization of a Phosphoinositide-mediated Odor Transduction Pathway Reveals Plasma Membrane Localization of an Inositol 1,4,5-Trisphosphate Receptor in Lobster Olfactory Receptor Neurons

“…Finally, PIs regulate the activity of a sodiumactivated channel that has been implicated in amplifying the transduction current in lobster ORNs (16,17). G q and phospholipase C proteins have been molecularly identified from the olfactory organ of clawed lobster (18,19). In an effort to characterize further the molecular substrate for PI signaling in lobster ORNs, we isolated cDNAs from spiny lobster olfactory organ that encode a protein conserved with IP 3 Rs, in addition to the G␣ q/11 protein.…”