A Gs-RhoGEF interaction: An old G protein finds a new job.

The heterotrimeric G proteins are known to have a variety of downstream effectors, but Gs was long thought to be specifically coupled to adenylyl cyclases. A new study indicates that activated Gs can also directly interact with a guanine nucleotide exchange factor for Rho family small GTPases, PDZ-RhoGEF. This novel interaction mediates activation of the small G protein Cdc42 by Gs-coupled GPCRs, inducing cytoskeletal rearrangements and formation of filopodia-like structures. Furthermore, overexpression of a minimal PDZ-RhoGEF fragment can down-regulate cAMP signaling, suggesting that this effector competes with canonical signaling. This first demonstration that the Gαs subfamily regulates activity of Rho GTPases extends our understanding of Gαs activity and establishes RhoGEF coupling as a universal Gα function.

The regulatory G protein signaling complex, Gß5-R7, promotes glucose- and extracellular signal-stimulated insulin secretion.

G protein-coupled receptors (GPCRs) are important modulators of glucose-stimulated insulin secretion, essential for maintaining energy homeostasis. Here we investigated the role of Gß5-R7, a protein complex consisting of the atypical G protein ß subunit Gß5 and a regulator of G protein signaling of the R7 family. Using the mouse insulinoma MIN6 cell line and pancreatic islets, we investigated the effects of G protein subunit ß 5 (Gnb5) knockout on insulin secretion. Consistent with previous work, Gnb5 knockout diminished insulin secretion evoked by the muscarinic cholinergic agonist Oxo-M. We found that the Gnb5 knockout also attenuated the activity of other GPCR agonists, including ADP, arginine vasopressin, glucagon-like peptide 1, and forskolin, and, surprisingly, the response to high glucose. Experiments with MIN6 cells cultured at different densities provided evidence that Gnb5 knockout eliminated the stimulatory effect of cell adhesion on Oxo-M-stimulated glucose-stimulated insulin secretion; this effect likely involved the adhesion GPCR GPR56. Gnb5 knockout did not influence cortical actin depolymerization but affected protein kinase C activity and the 14-3-3ϵ substrate. Importantly, Gnb5-/- islets or MIN6 cells had normal total insulin content and released normal insulin amounts in response to K+-evoked membrane depolarization. These results indicate that Gß5-R7 plays a role in the insulin secretory pathway downstream of signaling via all GPCRs and glucose. We propose that the Gß5-R7 complex regulates a phosphorylation event participating in the vesicular trafficking pathway downstream of G protein signaling and actin depolymerization but upstream of insulin granule release.

Inflammasome Activation Induces Pyroptosis in the Retina Exposed to Ocular Hypertension Injury.

Mechanical stress and hypoxia during episodes of ocular hypertension (OHT) trigger glial activation and neuroinflammation in the retina. Glial activation and release of pro-inflammatory cytokines TNFα and IL-1ß, complement, and other danger factors was shown to facilitate injury and loss of retinal ganglion cells (RGCs) that send visual information to the brain. However, cellular events linking neuroinflammation and neurotoxicity remain poorly characterized. Several pro-inflammatory and danger signaling pathways, including P2X7 receptors and Pannexin1 (Panx1) channels, are known to activate inflammasome caspases that proteolytically activate gasdermin D channel-formation to export IL-1 cytokines and/or induce pyroptosis. In this work, we used molecular and genetic approaches to map and characterize inflammasome complexes and detect pyroptosis in the OHT-injured retina. Acute activation of distinct inflammasome complexes containing NLRP1, NLRP3 and Aim2 sensor proteins was detected in RGCs, retinal astrocytes and Muller glia of the OHT-challenged retina. Inflammasome-mediated activation of caspases-1 and release of mature IL-1ß were detected within 6 h and peaked at 12-24 h after OHT injury. These coincided with the induction of pyroptotic pore protein gasdermin D in neurons and glia in the ganglion cell layer (GCL) and inner nuclear layer (INL). The OHT-induced release of cytokines and RGC death were significantly decreased in the retinas of Casp1-/-Casp4(11)del, Panx1-/- and in Wild-type (WT) mice treated with the Panx1 inhibitor probenecid. Our results showed a complex spatio-temporal pattern of innate immune responses in the retina. Furthermore, they indicate an active contribution of neuronal NLRP1/NLRP3 inflammasomes and the pro-pyroptotic gasdermin D pathway to pathophysiology of the OHT injury. These results support the feasibility of inflammasome modulation for neuroprotection in OHT-injured retinas.

Pannexin 1 sustains the electrophysiological responsiveness of retinal ganglion cells.

Pannexin 1 (Panx1) forms ATP-permeable membrane channels that play a key role in purinergic signaling in the nervous system in both normal and pathological conditions. In the retina, particularly high levels of Panx1 are found in retinal ganglion cells (RGCs), but the normal physiological function in these cells remains unclear. In this study, we used patch clamp recordings in the intact inner retina to show that evoked currents characteristic of Panx1 channel activity were detected only in RGCs, particularly in the OFF-type cells. The analysis of pattern electroretinogram (PERG) recordings indicated that Panx1 contributes to the electrical output of the retina. Consistently, PERG amplitudes were significantly impaired in the eyes with targeted ablation of the Panx1 gene in RGCs. Under ocular hypertension and ischemic conditions, however, high Panx1 activity permeated cell membranes and facilitated the selective loss of RGCs or stably transfected Neuro2A cells. Our results show that high expression of the Panx1 channel in RGCs is essential for visual function in the inner retina but makes these cells highly sensitive to mechanical and ischemic stresses. These findings are relevant to the pathophysiology of retinal disorders induced by increased intraocular pressure, such as glaucoma.

Teaching an Old Drug New Tricks: Agonism, Antagonism, and Biased Signaling of Pilocarpine through M3 Muscarinic Acetylcholine Receptor.

Pilocarpine is a prototypical drug used to treat glaucoma and dry mouth and is classified as either a full or partial muscarinic agonist. Here, we report several unexpected results pertaining to its interaction with muscarinic M3 receptor (M3R). We found that pilocarpine was 1000 times less potent in stimulating mouse-eye pupil constriction than muscarinic agonists oxotremorin-M (Oxo-M) or carbachol (CCh), although all three ligands have similar Kd values for M3R. In contrast to CCh or Oxo-M, pilocarpine does not induce Ca2+ mobilization via endogenous M3R in human embryonic kidney cell line 293T (HEK293T) or mouse insulinoma (MIN6) cells. Pilocarpine also fails to stimulate insulin secretion and, instead, antagonizes the insulinotropic effect of Oxo-M and CCh-induced Ca2+ upregulation; however, in HEK293T or Chinese hamster ovary-K1 cells overexpressing M3R, pilocarpine induces Ca2+ transients like those recorded with another cognate G protein-coupled muscarinic receptor, M1R. Stimulation of cells overexpressing M1R or M3R with CCh resulted in a similar reduction in phosphatidylinositol 4,5-bisphosphate (PIP2). In contrast to CCh, pilocarpine stimulated PIP2 hydrolysis only in cells overexpressing M1R but not M3R. Moreover, pilocarpine blocked CCh-stimulated PIP2 hydrolysis in M3R-overexpressing cells, thus, it acted as an antagonist. Pilocarpine activates extracellular regulated kinase 1/2 in MIN6 cells. The stimulatory effect on extracellular regulated kinase (ERK1/2) was blocked by the Src family kinase inhibitor PP2, indicating that the action of pilocarpine on endogenous M3R is biased toward ß-arrestin. Taken together, our findings show that pilocarpine can act as either an agonist or antagonist of M3R, depending on the cell type, expression level, and signaling pathway downstream of this receptor.

Regulator of G-protein signaling Gß5-R7 is a crucial activator of muscarinic M3 receptor-stimulated insulin secretion.

In pancreatic ß cells, muscarinic cholinergic receptor M3 (M3R) stimulates glucose-induced secretion of insulin. Regulator of G-protein signaling (RGS) proteins are critical modulators of GPCR activity, yet their role in ß cells remains largely unknown. R7 subfamily RGS proteins are stabilized by the G-protein subunit Gß5, such that the knockout of the Gnb5 gene results in degradation of all R7 subunits. We found that Gnb5 knockout in mice or in the insulin-secreting MIN6 cell line almost completely eliminates insulinotropic activity of M3R. Moreover, overexpression of Gß5-RGS7 strongly promotes M3R-stimulated insulin secretion. Examination of this noncanonical mechanism in Gnb5-/- MIN6 cells showed that cAMP, diacylglycerol, or Ca2+ levels were not significantly affected. There was no reduction in the amplitude of free Ca2+ responses in islets from the Gnb5-/- mice, but the frequency of Ca2+ oscillations induced by cholinergic agonist was lowered by more than 30%. Ablation of Gnb5 impaired M3R-stimulated phosphorylation of ERK1/2. Stimulation of the ERK pathway in Gnb5-/- cells by epidermal growth factor restored M3R-stimulated insulin release to near normal levels. Identification of the novel role of Gß5-R7 in insulin secretion may lead to a new therapeutic approach for improving pancreatic ß-cell function.-Wang, Q., Pronin, A. N., Levay, K., Almaca, J., Fornoni, A., Caicedo, A., Slepak, V. Z. Regulator of G-protein signaling Gß5-R7 is a crucial activator of muscarinic M3 receptor-stimulated insulin secretion.

Emerging roles of the single EF-hand Ca2+ sensor tescalcin in the regulation of gene expression, cell growth and differentiation.

Tescalcin (TESC, also known as calcineurin-homologous protein 3, CHP3) is a 24-kDa EF-hand Ca2+-binding protein that has recently emerged as a regulator of cell differentiation and growth. The TESC gene has also been linked to human brain abnormalities, and high expression of tescalcin has been found in several cancers. The expression level of tescalcin changes dramatically during development and upon signal-induced cell differentiation. Recent studies have shown that tescalcin is not only subjected to up- or down-regulation, but also has an active role in pathways that drive cell growth and differentiation programs. At the molecular level, there is compelling experimental evidence showing that tescalcin can directly interact with and regulate the activities of the Na+/H+ exchanger NHE1, subunit 4 of the COP9 signalosome (CSN4) and protein kinase glycogen-synthase kinase 3 (GSK3). In hematopoetic precursor cells, tescalcin has been shown to couple activation of the extracellular signal-regulated kinase (ERK) cascade to the expression of transcription factors that control cell differentiation. The purpose of this Commentary is to summarize recent efforts that have served to characterize the biochemical, genetic and physiological attributes of tescalcin, and its unique role in the regulation of various cellular functions.

Regulator of G Protein Signaling 7 (RGS7) Can Exist in a Homo-oligomeric Form That Is Regulated by Gαo and R7-binding Protein.

RGS (regulator of G protein signaling) proteins of the R7 subfamily (RGS6, -7, -9, and -11) are highly expressed in neurons where they regulate many physiological processes. R7 RGS proteins contain several distinct domains and form obligatory dimers with the atypical Gß subunit, Gß5 They also interact with other proteins such as R7-binding protein, R9-anchoring protein, and the orphan receptors GPR158 and GPR179. These interactions facilitate plasma membrane targeting and stability of R7 proteins and modulate their activity. Here, we investigated RGS7 complexes using in situ chemical cross-linking. We found that in mouse brain and transfected cells cross-linking causes formation of distinct RGS7 complexes. One of the products had the apparent molecular mass of ∼150 kDa on SDS-PAGE and did not contain Gß5 Mass spectrometry analysis showed no other proteins to be present within the 150-kDa complex in the amount close to stoichiometric with RGS7. This finding suggested that RGS7 could form a homo-oligomer. Indeed, co-immunoprecipitation of differentially tagged RGS7 constructs, with or without chemical cross-linking, demonstrated RGS7 self-association. RGS7-RGS7 interaction required the DEP domain but not the RGS and DHEX domains or the Gß5 subunit. Using transfected cells and knock-out mice, we demonstrated that R7-binding protein had a strong inhibitory effect on homo-oligomerization of RGS7. In contrast, our data indicated that GPR158 could bind to the RGS7 homo-oligomer without causing its dissociation. Co-expression of constitutively active Gαo prevented the RGS7-RGS7 interaction. These results reveal the existence of RGS protein homo-oligomers and show regulation of their assembly by R7 RGS-binding partners.

Elemental sulfur and acetate can support life of a novel strictly anaerobic haloarchaeon.

Archaea domain is comprised of many versatile taxa that often colonize extreme habitats. Here, we report the discovery of strictly anaerobic extremely halophilic euryarchaeon, capable of obtaining energy by dissimilatory reduction of elemental sulfur using acetate as the only electron donor and forming sulfide and CO2 as the only products. This type of respiration has never been observed in hypersaline anoxic habitats and is the first example of such metabolic capability in the entire Archaea domain. We isolated and cultivated these unusual organisms, selecting one representative strain, HSR2, for detailed characterization. Our studies including physiological tests, genome sequencing, gene expression, metabolomics and [(14)C]-bicarbonate assimilation assays revealed that HSR2 oxidized acetate completely via the tricarboxylic acid cycle. Anabolic assimilation of acetate occurred via activated glyoxylate bypass and anaplerotic carboxylation. HSR2 possessed sulfurtransferase and an array of membrane-bound polysulfide reductase genes, all of which were expressed during the growth. Our findings suggest the biogeochemical contribution of haloarchaea in hypersaline anoxic environments must be reconsidered.

Helix 8 and the i3 loop of the muscarinic M3 receptor are crucial sites for its regulation by the Gß5-RGS7 complex.

The muscarinic M3 receptor (M3R) is a Gq-coupled receptor and is known to interact with many intracellular regulatory proteins. One of these molecules is Gß5-RGS7, the permanently associated heterodimer of G protein ß-subunit Gß5 and RGS7, a regulator of G protein signaling. Gß5-RGS7 can attenuate M3R-stimulated release of Ca(2+) from intracellular stores or enhance the influx of Ca(2+) across the plasma membrane. Here we show that deletion of amino acids 304-345 from the central portion of the i3 loop renders M3R insensitive to regulation by Gß5-RGS7. In addition to the i3 loop, interaction of M3R with Gß5-RGS7 requires helix 8. According to circular dichroism spectroscopy, the peptide corresponding to amino acids 548-567 in the C-terminus of M3R assumes an α-helical conformation. Substitution of Thr553 and Leu558 with Pro residues disrupts this α-helix and abolished binding to Gß5-RGS7. Introduction of the double Pro substitution into full-length M3R (M3R(TP/LP)) prevents trafficking of the receptor to the cell surface. Using atropine or other antagonists as pharmacologic chaperones, we were able to increase the level of surface expression of the TP/LP mutant to levels comparable to that of wild-type M3R. However, M3R-stimulated calcium signaling is still severely compromised. These results show that the interaction of M3R with Gß5-RGS7 requires helix 8 and the central portion of the i3 loop.

Expression of olfactory signaling genes in the eye.

PURPOSE: To advance our understanding how the outer eye interacts with its environment, we asked which cellular receptors are expressed in the cornea, focusing on G protein-coupled receptors. METHODS: Total RNA from the mouse cornea was subjected to next-generation sequencing using the Illumina platform. The data was analyzed with TopHat and CuffLinks software packages. Expression of a representative group of genes detected by RNA-seq was further analyzed by RT-PCR and in situ hybridization using RNAscope technology and fluorescent microscopy. RESULTS: We generated more than 46 million pair-end reads from mouse corneal RNA. Bioinformatics analysis revealed that the mouse corneal transcriptome reconstructed from these reads represents over 10,000 gene transcripts. We identified 194 GPCR transcripts, of which 96 were putative olfactory receptors. RT-PCR analysis confirmed the presence of several olfactory receptors and related genes, including olfactory marker protein and the G protein associated with olfaction, Gαolf. In situ hybridization showed that mRNA for olfactory marker protein, Gαolf and possibly some olfactory receptors were found in the corneal epithelial cells. In addition to the corneal epithelium, Gαolf was present in the ganglionic and inner nuclear layers of the retina. One of the olfactory receptors, Olfr558, was present primarily in vessels of the eye co-stained with antibodies against alpha-smooth muscle actin, indicating expression in arterioles. CONCLUSIONS: Several species of mRNA encoding putative olfactory receptors and related genes are expressed in the mouse cornea and other parts of the eye indicating they may play a role in sensing chemicals in the ocular environment.

Differential effects of the Gß5-RGS7 complex on muscarinic M3 receptor-induced Ca2+ influx and release.

The G protein ß subunit Gß5 uniquely forms heterodimers with R7 family regulators of G protein signaling (RGS) proteins (RGS6, RGS7, RGS9, and RGS11) instead of Gγ. Although the Gß5-RGS7 complex attenuates Ca(2+) signaling mediated by the muscarinic M3 receptor (M3R), the route of Ca(2+) entry (i.e., release from intracellular stores and/or influx across the plasma membrane) is unknown. Here, we show that, in addition to suppressing carbachol-stimulated Ca(2+) release, Gß5-RGS7 enhanced Ca(2+) influx. This novel effect of Gß5-RGS7 was blocked by nifedipine and 2-aminoethoxydiphenyl borate. Experiments with pertussis toxin, an RGS domain-deficient mutant of RGS7, and UBO-QIC {L-threonine,(3R)-N-acetyl-3-hydroxy-L-leucyl-(aR)-a-hydroxybenzenepropanoyl-2,3-idehydro-N-methylalanyl-L-alanyl-N-methyl-L-alanyl-(3R)-3-[[(2S,3R)-3-hydroxy-4- methyl-1-oxo-2-[(1-oxopropyl)amino]pentyl]oxy]-L-leucyl-N,O-dimethyl-,(7→1)-lactone (9CI)}, a novel inhibitor of Gq, showed that Gß5-RGS7 modulated a Gq-mediated pathway. These studies indicate that Gß5-RGS7, independent of RGS7 GTPase-accelerating protein activity, couples M3R to a nifedipine-sensitive Ca(2+) channel. We also compared the action of Gß5-RGS7 on M3R-induced Ca(2+) influx and release elicited by different muscarinic agonists. Responses to Oxo-M [oxotremorine methiodide N,N,N,-trimethyl-4-(2-oxo-1-pyrrolidinyl)-2-butyn-1-ammonium iodide] were insensitive to Gß5-RGS7. Pilocarpine responses consisted of a large release and modest influx components, of which the former was strongly inhibited whereas the latter was insensitive to Gß5-RGS7. McN-A-343 [(4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride] was the only compound whose total Ca(2+) response was enhanced by Gß5-RGS7, attributed to, in part, by the relatively small Ca(2+) release this partial agonist stimulated. Together, these results show that distinct agonists not only have differential M3R functional selectivity, but also confer specific sensitivity to the Gß5-RGS7 complex.

Regulation of Cop9 signalosome activity by the EF-hand Ca2+-binding protein tescalcin.

The Ca(2+)-binding protein tescalcin is known to be involved in hematopoietic cell differentiation; however, this mechanism is poorly understood. Here, we identify CSN4 (subunit 4 of the COP9 signalosome) as a novel binding partner of tescalcin. The COP9 signalosome (CSN) is a multiprotein complex that is essential for development in all eukaryotes. This interaction is selective, Ca(2+)-dependent and involves the PCI domain of CSN4 subunit. We then investigated tescalcin and CSN activity in human erythroleukemia HEL and promyelocytic leukemia K562 cells and find that phorbol 12-myristate 13-acetate (PMA)-induced differentiation, resulting in the upregulation of tescalcin, coincides with reduced deneddylation of cullin-1 (Cul1) and stabilization of p27(Kip1) - molecular events that are associated with CSN activity. The knockdown of tescalcin led to an increase in Cul1 deneddylation, expression of F-box protein Skp2 and the transcription factor c-Jun, whereas the levels of cell cycle regulators p27(Kip1) and p53 decreased. These effects are consistent with the hypothesis that tescalcin might play a role as a negative regulator of CSN activity towards Cul1 in the process of induced cell differentiation.

Molecular pathways of pannexin1-mediated neurotoxicity.

Pannexin1 (Panx1) forms non-selective membrane channels, structurally similar to gap junction hemichannels, and are permeable to ions, nucleotides, and other small molecules below 900 Da. Panx1 activity has been implicated in paracrine signaling and inflammasome regulation. Recent studies in different animal models showed that overactivation of Panx1 correlates with a selective demise of several types of neurons, including retinal ganglion cells, brain pyramidal, and enteric neurons. The list of Panx1 activators includes extracellular ATP, glutamate, high K(+), Zn(2+), fibroblast growth factors (FGFs),pro-inflammatory cytokines, and elevation of intracellular Ca(2+). Most of these molecules are released following mechanical, ischemic, or inflammatory injury of the CNS, and rapidly activate the Panx1 channel. Prolonged opening of Panx1 channel induced by these "danger signals" triggers a cascade of neurotoxic events capable of killing cells. The most vulnerable cell type are neurons that express high levels of Panx1. Experimental evidence suggests that Panx1 channels mediate at least two distinct neurotoxic processes: increased permeability of the plasma membrane and activation of the inflammasome in neurons and glia. Importantly, both pharmacological and genetic inactivation of Panx1 suppresses both these processes, providing a marked protection in several disease and injury models. These findings indicate that external danger signals generated after diverse types of injuries converge to activate Panx1. In this review we discuss molecular mechanisms associated with Panx1 toxicity and the crosstalk between different pathways.

From mechanosensitivity to inflammatory responses: new players in the pathology of glaucoma.

PURPOSE OF THE STUDY: Many blinding diseases of the inner retina are associated with degeneration and loss of retinal ganglion cells (RGCs). Recent evidence implicates several new signaling mechanisms as causal agents associated with RGC injury and remodeling of the optic nerve head. Ion channels such as Transient receptor potential vanilloid isoform 4 (TRPV4), pannexin-1 (Panx1) and P2X7 receptor are localized to RGCs and act as potential sensors and effectors of mechanical strain, ischemia and inflammatory responses. Under normal conditions, TRPV4 may function as an osmosensor and a polymodal molecular integrator of diverse mechanical and chemical stimuli, whereas P2X7R and Panx1 respond to stretch- and/or swelling-induced adenosine triphosphate release from neurons and glia. Ca(2+) influx, induced by stimulation of mechanosensitive ion channels in glaucoma, is proposed to influence dendritic and axonal remodeling that may lead to RGC death while (at least initially) sparing other classes of retinal neuron. The secondary phase of the retinal glaucoma response is associated with microglial activation and an inflammatory response involving Toll-like receptors (TLRs), cluster of differentiation 3 (CD3) immune recognition molecules associated with the T-cell antigen receptor, complement molecules and cell type-specific release of neuroactive cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß). The retinal response to mechanical stress thus involves a diversity of signaling pathways that sense and transduce mechanical strain and orchestrate both protective and destructive secondary responses. CONCLUSIONS: Mechanistic understanding of the interaction between pressure-dependent and independent pathways is only beginning to emerge. This review focuses on the molecular basis of mechanical strain transduction as a primary mechanism that can damage RGCs. The damage occurs through Ca(2+)-dependent cellular remodeling and is associated with parallel activation of secondary ischemic and inflammatory signaling pathways. Molecules that mediate these mechanosensory and immune responses represent plausible targets for protecting ganglion cells in glaucoma, optic neuritis and retinal ischemia.

Microbial life in the Lake Medee, the largest deep-sea salt-saturated formation.

Deep-sea hypersaline anoxic lakes (DHALs) of the Eastern Mediterranean represent some of the most hostile environments on our planet. We investigated microbial life in the recently discovered Lake Medee, the largest DHAL found to-date. Medee has two unique features: a complex geobiochemical stratification and an absence of chemolithoautotrophic Epsilonproteobacteria, which usually play the primary role in dark bicarbonate assimilation in DHALs interfaces. Presumably because of these features, Medee is less productive and exhibits reduced diversity of autochthonous prokaryotes in its interior. Indeed, the brine community almost exclusively consists of the members of euryarchaeal MSBL1 and bacterial KB1 candidate divisions. Our experiments utilizing cultivation and [(14)C]-assimilation, showed that these organisms at least partially rely on reductive cleavage of osmoprotectant glycine betaine and are engaged in trophic cooperation. These findings provide novel insights into how prokaryotic communities can adapt to salt-saturated conditions and sustain active metabolism at the thermodynamic edge of life.

Partaking of Archaea to biogeochemical cycling in oxygen-deficient zones of meromictic saline Lake Faro (Messina, Italy).

We used a combination of molecular and microbiological approaches to determine the activity, abundance and diversity of archaeal populations inhabiting meromictic saline Lake Faro (Messina, Italy). Analysis of archaeal 16S rRNA, amoA, accA and hbd genes and transcripts revealed that sub- and anoxic layers of Lake Faro are primarily inhabited by the organisms related to the clusters of Marine Group I.1a of Thaumarchaeota frequently recovered from oxygen-depleted marine ecosystems. These organisms dominated the metabolically active archaea down to the bottom of the lake, indicating their adaptation to recurrent changes in the levels of water column hypoxia. The upper microaerobic layer of Lake Faro redoxcline has the maximal rates of dark primary production much lower than those of other previously studied pelagic redoxclines, but comparable to the values of meso- and bathypelagic areas of Mediterranean Sea. Application of bacterial inhibitors, especially azide, significantly declined the CO2 fixation rates in the low interface and monimolimnion, whereas archaea-specific inhibitor had effect only in upper part of the redoxcline. Based on these findings, we hypothesize that dark bicarbonate fixation in suboxic zone of Lake Faro results mainly from archaeal activity which is affected by the predicted lack in oxygen in lower layers.

Evidence for multiple phototransduction pathways in a reef-building coral.

Photosensitive behaviors and circadian rhythms are well documented in reef-building corals and their larvae, but the mechanisms responsible for photoreception have not been described in these organisms. Here we report the cloning, immunolocalization, and partial biochemical characterization of three opsins and four G proteins expressed in planulae of the Caribbean elkhorn coral, Acropora palmata. All three opsins (acropsins 1-3) possess conserved seven-pass transmembrane structure, and localize to distinct regions of coral planulae. Acropsin 1 was localized in the larval endoderm, while acropsin 2 was localized in solitary cells of the ectoderm. These rod-like cells displayed a remarkably polarized distribution, concentrated in the aboral end. We also cloned four A. palmata G protein alpha subunits. Three were homologs of vertebrate Gi, Go, and Gq. The fourth is presumably a novel G protein, which displays only 40% identity with the nearest known G protein, and we termed it Gc for "cnidarian". We show that Gc and Gq can be activated by acropsins in a light-dependent manner in vitro. This indicates that at least acropsins 1 and 3 can form functional photoreceptors and potentially may play a role in color preference during settlement, vertical positioning and other light-guided behaviors observed in coral larvae.

Subcellular localization of regulator of G protein signaling RGS7 complex in neurons and transfected cells.

The R7 family of regulators of G protein signaling (RGS) is involved in many functions of the nervous system. This family includes RGS6, RGS7, RGS9, and RGS11 gene products and is defined by the presence of the characteristic first found in Disheveled, Egl-10, Pleckstrin (DEP), DEP helical extension (DHEX), Gγ-like, and RGS domains. Herein, we examined the subcellular localization of RGS7, the most broadly expressed R7 member. Our immunofluorescence studies of retinal and dorsal root ganglion neurons showed that RGS7 concentrated at the plasma membrane of cell bodies, in structures resembling lamellipodia or filopodia along the processes, and at the dendritic tips. At the plasma membrane of dorsal root ganglia neurons, RGS7 co-localized with its known binding partners R7 RGS binding protein (R7BP), Gαo, and Gαq. More than 50% of total RGS7-specific immunofluorescence was present in the cytoplasm, primarily within numerous small puncta that did not co-localize with R7BP. No specific RGS7 or R7BP immunoreactivity was detected in the nuclei. In transfected cell lines, ectopic RGS7 had both diffuse cytosolic and punctate localization patterns. RGS7 also localized in centrosomes. Structure-function analysis showed that the punctate localization was mediated by the DEP/DHEX domains, and centrosomal localization was dependent on the DHEX domain.