Heterozygous mice with Ric-8 mutation exhibit impaired spatial memory and decreased anxiety

Targeted deletion of RIC8A in mouse neural precursor cells interferes with the development of the brain, eyes, and muscles

Autosomal recessive disorders such as Fukuyama congenital muscular dystrophy, Walker-Warburg syndrome, and the muscle-eye-brain disease are characterized by defects in the development of patient's brain, eyes, and skeletal muscles. These syndromes are accompanied by brain malformations like type II lissencephaly in the cerebral cortex with characteristic overmigrations of neurons through the breaches of the pial basement membrane. The signaling pathways activated by laminin receptors, dystroglycan and integrins, control the integrity of the basement membrane, and their malfunctioning may underlie the pathologies found in the rise of defects reminiscent of these syndromes. Similar defects in corticogenesis and neuromuscular disorders were found in mice when RIC8A was specifically removed from neural precursor cells. RIC8A regulates a subset of G-protein α subunits and in several model organisms, it has been reported to participate in the control of cell division, signaling, and migration. Here, we studied the role of RIC8A in the development of the brain, muscles, and eyes of the neural precursor-specific conditional Ric8a knockout mice. The absence of RIC8A severely affected the attachment and positioning of radial glial processes, Cajal-Retzius' cells, and the arachnoid trabeculae, and these mice displayed additional defects in the lens, skeletal muscles, and heart development. All the discovered defects might be linked to aberrancies in cell adhesion and migration, suggesting that RIC8A has a crucial role in the regulation of cell-extracellular matrix interactions and that its removal leads to the phenotype characteristic to type II lissencephaly-associated diseases. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 374-390, 2018.

Regulation, Signaling, and Physiological Functions of G-Proteins

Heterotrimeric guanine-nucleotide-binding regulatory proteins (G-proteins) mainly relay the information from G-protein-coupled receptors (GPCRs) on the plasma membrane to the inside of cells to regulate various biochemical functions. Depending on the targeted cell types, tissues, and organs, these signals modulate diverse physiological functions. The basic schemes of heterotrimeric G-proteins have been outlined. In this review, we briefly summarize what is known about the regulation, signaling, and physiological functions of G-proteins. We then focus on a few less explored areas such as the regulation of G-proteins by non-GPCRs and the physiological functions of G-proteins that cannot be easily explained by the known G-protein signaling pathways. There are new signaling pathways and physiological functions for G-proteins to be discovered and further interrogated. With the advancements in structural and computational biological techniques, we are closer to having a better understanding of how G-proteins are regulated and of the specificity of G-protein interactions with their regulators.

The CREB Transcription Factor Controls Transcriptional Activity of the Human RIC8B Gene

Proper regulation of gene expression is essential for normal development, cellular growth, and differentiation. Differential expression profiles of mRNA coding for vertebrate Ric-8B during embryo and adult stages have been observed. In addition, Ric-8B is expressed in few cerebral nuclei subareas. These facts point to a dynamic control of RIC8B gene expression. In order to understand the transcriptional regulation of this gene, we searched for cis-elements in the sequence of the human RIC8B promoter region, identifying binding sites for the basic/leucine zipper (bZip) CREB transcription factor family (CRE sites) and C/EBP transcription factor family (C/EBP sites). CRE sites were found clustered near the transcription start site, while the C/EBP sites were found clustered at around 300 bp upstream the CRE sites. Here, we demonstrate the ability of CREB1 and C/EBPβ to bind their respective elements identified in the RIC8B promoter. Comparative protein-DNA interaction analyses revealed only the proximal elements as high affinity sites for CREB1 and only the distal elements as high affinity sites for C/EBPβ. Chromatin immunoprecipitation analyses, carried out using a human neuroblastoma cell line, confirmed the preferential association of CREB to the proximal region of the RIC8B promoter. By performing luciferase reporter assays, we found the CRE sites as the most relevant elements for its transcriptional activity. Taken together, these data show the existence of functional CREB and C/EBP binding sites in the human RIC8B gene promoter, a particular distribution of these sites and demonstrate a relevant role of CREB in stimulating transcriptional activity of this gene. J. Cell. Biochem. 117: 1797-1805, 2016. © 2016 Wiley Periodicals, Inc.

Expression Pattern and Localization Dynamics of Guanine Nucleotide Exchange Factor RIC8 during Mouse Oogenesis

Targeting of G proteins to the cell cortex and their activation is one of the triggers of both asymmetric and symmetric cell division. Resistance to inhibitors of cholinesterase 8 (RIC8), a guanine nucleotide exchange factor, activates a certain subgroup of G protein α-subunits in a receptor independent manner. RIC8 controls the asymmetric cell division in Caenorhabditis elegans and Drosophila melanogaster, and symmetric cell division in cultured mammalian cells, where it regulates the mitotic spindle orientation. Although intensely studied in mitosis, the function of RIC8 in mammalian meiosis has remained unknown. Here we demonstrate that the expression and subcellular localization of RIC8 changes profoundly during mouse oogenesis. Immunofluorescence studies revealed that RIC8 expression is dependent on oocyte growth and cell cycle phase. During oocyte growth, RIC8 is abundantly present in cytoplasm of oocytes at primordial, primary and secondary preantral follicle stages. Later, upon oocyte maturation RIC8 also populates the germinal vesicle, its localization becomes cell cycle dependent, and it associates with chromatin and the meiotic spindle. After fertilization, RIC8 protein converges to the pronuclei and is also detectable at high levels in the nucleolus precursor bodies of both maternal and paternal pronucleus. During first cleavage of zygote RIC8 localizes in the mitotic spindle and cell cortex of forming blastomeres. In addition, we demonstrate that RIC8 co-localizes with its interaction partners Gα_i1/2:GDP and LGN in meiotic/mitotic spindle, cell cortex and polar bodies of maturing oocytes and zygotes. Downregulation of Ric8 by siRNA leads to interferred translocation of Gα_i1/2 to cortical region of maturing oocytes and reduction of its levels. RIC8 is also expressed at high level in female reproductive organs e.g. oviduct. Therefore we suggest a regulatory function for RIC8 in mammalian gametogenesis and fertility.

Activators of G protein signaling in the kidney

Heterotrimeric G proteins play a crucial role in regulating signal processing to maintain normal cellular homeostasis, and subtle perturbations in its activity can potentially lead to the pathogenesis of renal disorders or diseases. Cell-surface receptors and accessory proteins, which normally modify and organize the coupling of individual G protein subunits, contribute to the regulation of heterotrimeric G protein activity and their convergence and/or divergence of downstream signaling initiated by effector systems. Activators of G protein signaling (AGS) are a family of accessory proteins that intervene at multiple distinct points during the activation-inactivation cycle of G proteins, even in the absence of receptor stimulation. Perturbations in the expression of individual AGS proteins have been reported to modulate signal transduction pathways in a wide array of diseases and disorders within the brain, heart, immune system, and more recently, the kidney. This review will provide an overview of the expression profile, localization, and putative biologic role of the AGS family in the context of normal and diseased states of the kidney.

Localization and expression profile of Group I and II Activators of G-protein Signaling in the kidney

Activators of G-protein Signaling (AGS) are a family of accessory proteins that were discovered as modulators of heterotrimeric G-protein subunits. The primary aim of the present study was to localize Group I and II AGS proteins and determine the renal expression profile using immunohistochemistry and quantitative RT-PCR, respectively, during normal and injured states of the kidney. Group I AGS1 was found to be predominantly localized to the proximal tubule, Group II AGS3 and AGS5 were exclusively localized to the distal tubular segments, and Group II AGS6 was ubiquitously expressed in every nephron segment of the rodent kidney. In rat kidneys following ischemia-reperfusion injury (IRI), Group I AGS1 mRNA was dramatically increased after 24 h by fivefold (P < 0.05), whereas Group II AGS3 and AGS4 mRNA was significantly decreased at the same time point (P < 0.05). No significant change in the transcript levels were detected at other time points for any of the AGS genes between control and IRI groups. In polycystic diseased kidneys, mRNA levels for AGS3, AGS4 and AGS6 was significantly increased (P < 0.05) by 75-80 % in PCK rat kidneys. The identification of Group I and II AGS mRNA and protein in the kidney may provide insight into the potential mechanism of action during normal and varying states of renal disease or injury.

Implications of non-canonical G-protein signaling for the immune system

Heterotrimeric guanine nucleotide-binding proteins (G proteins), which consist of three subunits α, β, and γ, function as molecular switches to control downstream effector molecules activated by G protein-coupled receptors (GPCRs). The GTP/GDP binding status of Gα transmits information about the ligand binding state of the GPCR to intended signal transduction pathways. In immune cells heterotrimeric G proteins impact signal transduction pathways that directly, or indirectly, regulate cell migration, activation, survival, proliferation, and differentiation. The cells of the innate and adaptive immune system abundantly express chemoattractant receptors and lesser amounts of many other types of GPCRs. But heterotrimeric G-proteins not only function in classical GPCR signaling, but also in non-canonical signaling. In these pathways the guanine exchange factor (GEF) exerted by a GPCR in the canonical pathway is replaced or supplemented by another protein such as Ric-8A. In addition, other proteins such as AGS3-6 can compete with Gβγ for binding to GDP bound Gα. This competition can promote Gβγ signaling by freeing Gβγ from rapidly rebinding GDP bound Gα. The proteins that participate in these non-canonical signaling pathways will be briefly described and their role, or potential one, in cells of the immune system will be highlighted.

Activators of G protein signaling exhibit broad functionality and define a distinct core signaling triad

Activators of G protein signaling (AGS), initially discovered in the search for receptor-independent activators of G protein signaling, define a broad panel of biologic regulators that influence signal transfer from receptor to G-protein, guanine nucleotide binding and hydrolysis, G protein subunit interactions, and/or serve as alternative binding partners for Gα and Gβγ independently of the classic heterotrimeric Gαβγ. AGS proteins generally fall into three groups based upon their interaction with and regulation of G protein subunits: group I, guanine nucleotide exchange factors (GEF); group II, guanine nucleotide dissociation inhibitors; and group III, entities that bind to Gβγ. Group I AGS proteins can engage all subclasses of G proteins, whereas group II AGS proteins primarily engage the Gi/Go/transducin family of G proteins. A fourth group of AGS proteins with selectivity for Gα16 may be defined by the Mitf-Tfe family of transcription factors. Groups I-III may act in concert, generating a core signaling triad analogous to the core triad for heterotrimeric G proteins (GEF + G proteins + effector). These two core triads may function independently of each other or actually cross-integrate for additional signal processing. AGS proteins have broad functional roles, and their discovery has advanced new concepts in signal processing, cell and tissue biology, receptor pharmacology, and system adaptation, providing unexpected platforms for therapeutic and diagnostic development.

Atypical protein kinase Cλ is critical for growth factor receptor-induced dorsal ruffle turnover and cell migration

Gα13, a member of the heterotrimeric G proteins, is critical for actin cytoskeletal reorganization and cell migration. Previously we have shown that Gα13 is essential for both G protein-coupled receptor and receptor tyrosine kinase-induced actin cytoskeletal reorganization such as dynamic dorsal ruffle turnover and cell migration. Ric-8A, a non-receptor guanine nucleotide exchange factor for some heterotrimeric G proteins, is critical for coupling receptor tyrosine kinases to Gα13. Here, we show that PDGF can induce phosphorylation of Ric-8A. Atypical protein kinase Cλ (aPKCλ) is required for Ric-8A phosphorylation. Furthermore, aPKCλ is required for PDGF-induced dorsal ruffle turnover and cell migration as demonstrated by both down-regulation of aPKCλ protein levels in cells by RNA interference and by studies in aPKCλ knock-out cells. Moreover, phosphorylation of Ric-8A modulates its subcellular localization. Hence, aPKCλ is critical for PDGF-induced actin cytoskeletal reorganization and cell migration.

Ablation of RIC8A function in mouse neurons leads to a severe neuromuscular phenotype and postnatal death

Resistance to inhibitors of cholinesterase 8 (RIC8) is a guanine nucleotide exchange factor required for the intracellular regulation of G protein signalling. RIC8 activates different Gα subunits via non-canonical pathway, thereby amplifying and prolonging the G protein mediated signal. In order to circumvent the embryonic lethality associated with the absence of RIC8A and to study its role in the nervous system, we constructed Ric8a conditional knockout mice using Cre/loxP technology. Introduction of a synapsin I promoter driven Cre transgenic mouse strain (SynCre) into the floxed Ric8a (Ric8a (F/F) ) background ablated RIC8A function in most differentiated neuron populations. Mutant SynCre (+/-) Ric8 (lacZ/F) mice were born at expected Mendelian ratio, but they died in early postnatal age (P4-P6). The mutants exhibited major developmental defects, like growth retardation and muscular weakness, impaired coordination and balance, muscular spasms and abnormal heart beat. Histological analysis revealed that the deficiency of RIC8A in neurons caused skeletal muscle atrophy and heart muscle hypoplasia, in addition, the sinoatrial node was misplaced and its size reduced. However, we did not observe gross morphological changes in brains of SynCre (+/-) Ric8a (lacZ/F) mutants. Our results demonstrate that in mice the activity of RIC8A in neurons is essential for survival and its deficiency causes a severe neuromuscular phenotype.

Ric-8A, a guanine nucleotide exchange factor for heterotrimeric G proteins, is critical for cranial neural crest cell migration

The neural crest (NC) is a transient embryonic structure induced at the border of the neural plate. NC cells extensively migrate towards diverse regions of the embryo, where they differentiate into various derivatives, including most of the craniofacial skeleton and the peripheral nervous system. The Ric-8A protein acts as a guanine nucleotide exchange factor for several Gα subunits, and thus behaves as an activator of signaling pathways mediated by heterotrimeric G proteins. Using in vivo transplantation assays, we demonstrate that Ric-8A levels are critical for the migration of cranial NC cells and their subsequent differentiation into craniofacial cartilage during Xenopus development. NC cells explanted from Ric-8A morphant embryos are unable to migrate directionally towards a source of the Sdf1 peptide, a potent chemoattractant for NC cells. Consistently, Ric-8A knock-down showed anomalous radial migratory behavior, displaying a strong reduction in cell spreading and focal adhesion formation. We further show that during in vivo and in vitro neural crest migration, Ric-8A localizes to the cell membrane, in agreement with its role as a G protein activator. We propose that Ric-8A plays essential roles during the migration of cranial NC cells, possibly by regulating cell adhesion and spreading.

Dictyostelium Ric8 is a nonreceptor guanine exchange factor for heterotrimeric G proteins and is important for development and chemotaxis

Heterotrimeric G proteins couple external signals to the activation of intracellular signal transduction pathways. Agonist-stimulated guanine nucleotide exchange activity of G-protein-coupled receptors results in the exchange of G-protein-bound GDP to GTP and the dissociation and activation of the complex into Gα-GTP and a Gβγ dimer. In Dictyostelium, a basal chemotaxis pathway consisting of heterotrimeric and monomeric G proteins is sufficient for chemotaxis. Symmetry breaking and amplification of chemoattractant sensing occurs between heterotrimeric G protein signaling and Ras activation. In a pull-down screen coupled to mass spectrometry, with Gα proteins as bait, we have identified resistant to inhibitors of cholinesterase 8 (Ric8) as a nonreceptor guanine nucleotide exchange factor for Gα-protein. Ric8 is not essential for the initial activation of heterotrimeric G proteins or Ras by uniform chemoattractant; however, it amplifies Gα signaling, which is essential for Ras-mediated symmetry breaking during chemotaxis and development.

Ric-8a, a guanine nucleotide exchange factor for heterotrimeric G proteins, regulates bergmann glia-basement membrane adhesion during cerebellar foliation

The cerebellum consists of an intricate array of lobules that arises during the process of foliation. Foliation not only increases surface area, but may also facilitate organization of cerebellar neural circuitry. Defects in cerebellar foliation are associated with a number of diseases. Yet, little is known about how foliation, a process involving large-scale and simultaneous movement of several different cell types, is coordinated by cell-cell signaling at the molecular level. Here we show that Ric-8a, a guanine nucleotide exchange factor in the G-protein-coupled receptor pathway, is specifically required in Bergmann glia during cerebellar foliation. We find that ric-8a mutation in mice results in disorganized Bergmann glial scaffolding, defective granule cell migration, and disrupted Purkinje cell positioning. These abnormalities result from primary defects in Bergmann glia since mutations in granule cells do not show similar effects. They first arise during late embryogenesis, at the onset of foliation, when ric-8a mutant Bergmann glia fail to maintain adhesion to the basement membrane specifically at emerging fissures. This suggests that Ric-8a is essential for the enhanced Bergmann glia-basement membrane adhesion required for fissure formation. Indeed, we find that ric-8a-deficient cerebellar glia show decreased affinity for basement membrane components. We also find that weakening Bergmann glia-basement membrane interaction by β1 integrin deletion results in a similar phenotype. These results thus reveal a novel role of Ric-8a in modulating Bergmann glia-basement membrane adhesion during foliation, and provide new insights into the signaling pathways that coordinate cellular movement during cerebellar morphogenesis.

Assembly and function of the regulator of G protein signaling 14 (RGS14)·H-Ras signaling complex in live cells are regulated by Gαi1 and Gαi-linked G protein-coupled receptors

Regulator of G protein signaling 14 (RGS14) is a multifunctional scaffolding protein that integrates heterotrimeric G protein and H-Ras signaling pathways. RGS14 possesses an RGS domain that binds active Gα(i/o)-GTP subunits to promote GTP hydrolysis and a G protein regulatory (GPR) motif that selectively binds inactive Gα(i1/3)-GDP subunits to form a stable heterodimer at cellular membranes. RGS14 also contains two tandem Ras/Rap binding domains (RBDs) that bind H-Ras. Here we show that RGS14 preferentially binds activated H-Ras-GTP in live cells to enhance H-Ras cellular actions and that this interaction is regulated by inactive Gα(i1)-GDP and G protein-coupled receptors (GPCRs). Using bioluminescence resonance energy transfer (BRET) in live cells, we show that RGS14-Luciferase and active H-Ras(G/V)-Venus exhibit a robust BRET signal at the plasma membrane that is markedly enhanced in the presence of inactive Gα(i1)-GDP but not active Gα(i1)-GTP. Active H-Ras(G/V) interacts with a native RGS14·Gα(i1) complex in brain lysates, and co-expression of RGS14 and Gα(i1) in PC12 cells greatly enhances H-Ras(G/V) stimulatory effects on neurite outgrowth. Stimulation of the Gα(i)-linked α(2A)-adrenergic receptor induces a conformational change in the Gα(i1)·RGS14·H-Ras(G/V) complex that may allow subsequent regulation of the complex by other binding partners. Together, these findings indicate that inactive Gα(i1)-GDP enhances the affinity of RGS14 for H-Ras-GTP in live cells, resulting in a ternary signaling complex that is further regulated by GPCRs.

Ric-8: different cellular roles for a heterotrimeric G-protein GEF

Signaling via heterotrimeric G-proteins is evoked by agonist-mediated stimulation of seven transmembrane spanning receptors (GPCRs). During the last decade it has become apparent that Gα subunits can be activated by receptor-independent mechanisms. Ric-8 belongs to a highly conserved protein family that regulates heterotrimeric G-protein function, acting as a non-canonical guanine nucleotide exchange factors (GEF) over a subset of Gα subunits. In this review we discuss the roles of Ric-8 in the regulation of diverse cell functions, emphasizing the contribution of its multiple domain protein structure in these diverse functions.

NCAM180 Regulates Ric8A Membrane Localization and Potentiates β-Adrenergic Response

Cooperation between receptors allows integrated intracellular signaling leading to appropriate physiological responses. The Neural Cell Adhesion Molecule (NCAM) has three main isoforms of 120, 140 and 180 kDa, with adhesive and signaling properties, but their respective functions remains to be fully identified. Here we show that the human NCAM180 intracellular domain is a novel interactor of the human guanosine exchange factor (GEF) Ric8A using the yeast two hybrid system and immunoprecipitation. Furthermore, NCAM, Ric8A and G_αs form a tripartite complex. Colocalization experiments by confocal microscopy revealed that human NCAM180 specifically induces the recruitment of Ric8A to the membrane. In addition, using an in vitro recombinant system, and in vivo by comparing NCAM knock-out mouse brain to NCAM heterozygous and wild type brains, we show that NCAM expression dose dependently regulates Ric8A redistribution in detergent resistent membrane microdomains (DRM). Previous studies have demonstrated essential roles for Ric8 in G_α protein activity at G protein coupled receptors (GPCR), during neurotransmitter release and for asymmetric cell division. We observed that inhibition of Ric8A by siRNA or its overexpression, decreases or increases respectively, cAMP production following β-adrenergic receptor stimulation. Furthermore, in human HEK293T recombinant cells, NCAM180 potentiates the G_αs coupled β-adrenergic receptor response, in a Ric8A dependent manner, whereas NCAM120 or NCAM140 do not. Finally, in mouse hippocampal neurons expressing endogenously NCAM, NCAM is required for the agonist isoproterenol to induce cAMP production, and this requirement depends on Ric8A. These data illustrate a functional crosstalk between a GPCR and an IgCAM in the nervous system.

Resistance to inhibitors of cholinesterase-8A (Ric-8A) is critical for growth factor receptor-induced actin cytoskeletal reorganization

Heterotrimeric G proteins are critical transducers of cellular signaling. In addition to their classic roles in relaying signals from G protein-coupled receptors (GPCRs), heterotrimeric G proteins also mediate physiological functions from non-GPCRs. Previously, we have shown that Gα(13), a member of the heterotrimeric G proteins, is essential for growth factor receptor-induced actin cytoskeletal reorganization such as dynamic dorsal ruffle turnover and cell migration. These Gα(13)-mediated dorsal ruffle turnover and cell migration by growth factors acting on their receptor tyrosine kinases (RTKs) are independent of GPCRs. However, the mechanism by which RTKs signal to Gα(13) is not known. Here, we show that cholinesterase-8A (Ric-8A), a nonreceptor guanine nucleotide exchange factor for some heterotrimeric G proteins, is critical for coupling RTKs to Gα(13). Down-regulation of Ric-8A protein levels in cells by RNA interference slowed down platelet-derived growth factor (PDGF)-induced dorsal ruffle turnover and inhibited PDGF-initiated cell migration. PDGF was able to increase the activity of Ric-8A in cells. Furthermore, purified Ric-8A proteins interact directly with purified Gα(13) protein in a nucleotide-dependent manner. Deficiency of Ric-8A prevented the translocation of Gα(13) to the cell cortex. Hence, Ric-8A is critical for growth factor receptor-induced actin cytoskeletal reorganization.

Cloning and spatiotemporal expression of RIC-8 in Xenopus embryogenesis

RIC-8 is a highly conserved protein that promotes G protein signaling as it acts as a Guanine nucleotide Exchanging Factor (GEF) over a subset of Gα subunits. In invertebrates, RIC-8 plays crucial roles in synaptic transmission as well as in asymmetric cell division. As a first step to address further studies on RIC-8 function in vertebrates, here we have cloned a ric-8 gene from Xenopus tropicalis (xtric-8) and determined its spatiotemporal expression pattern throughout embryogenesis. The xtric-8 transcript is expressed maternally and zygotically and, as development proceeds, it shows a dynamic expression pattern. At early developmental stages, xtric-8 is expressed in the animal hemisphere, whereas its expression is later restricted to neural tissues, such as the neural tube and the brain, as well as in the eye and neural crest-derived structures, including those of the craniofacial region. Together, our findings suggest that RIC-8 functions are related to the development of the nervous system.

Nucleotide exchange factor RIC-8 is indispensable in mammalian early development

The guanine nucleotide exchange factor RIC-8 is a conserved protein essential for the asymmetric division in the early embryogenesis in different organisms. The function of RIC-8 in mammalian development is not characterized so far. In this study we map the expression of RIC-8 during the early development of mouse. To elucidate the RIC-8 function we used Ric-8(-/-) mutant embryos. The Ric-8(-/-) embryos reach the gastrulation stage but do not develop further and die at E6.5-E8.5. We characterized the Ric-8(-/-) embryonic phenotype by morphological and marker gene analyses. The gastrulation is initiated in Ric-8(-/-) embryos but their growth is retarded, epiblast and mesoderm disorganized. Additionally, the basement membrane is defective, amnion folding and the formation of allantois are interfered, also the cavitation. Furthermore, the orientation of the Ric-8(-/-) embryo in the uterus was abnormal. Our study reveals that the activity of RIC-8 protein is irreplaceable for the correct gastrulation of mouse embryo.

Activation of the regulator of G protein signaling 14-Gαi1-GDP signaling complex is regulated by resistance to inhibitors of cholinesterase-8A

RGS14 is a brain scaffolding protein that integrates G protein and MAP kinase signaling pathways. Like other RGS proteins, RGS14 is a GTPase activating protein (GAP) that terminates Gαi/o signaling. Unlike other RGS proteins, RGS14 also contains a G protein regulatory (also known as GoLoco) domain that binds Gαi1/3-GDP in cells and in vitro. Here we report that Ric-8A, a nonreceptor guanine nucleotide exchange factor (GEF), functionally interacts with the RGS14-Gαi1-GDP signaling complex to regulate its activation state. RGS14 and Ric-8A are recruited from the cytosol to the plasma membrane in the presence of coexpressed Gαi1 in cells, suggesting formation of a functional protein complex with Gαi1. Consistent with this idea, Ric-8A stimulates dissociation of the RGS14-Gαi1-GDP complex in cells and in vitro using purified proteins. Purified Ric-8A stimulates dissociation of the RGS14-Gαi1-GDP complex to form a stable Ric-8A-Gαi complex in the absence of GTP. In the presence of an activating nucleotide, Ric-8A interacts with the RGS14-Gαi1-GDP complex to stimulate both the steady-state GTPase activity of Gαi1 and binding of GTP to Gαi1. However, sufficiently high concentrations of RGS14 competitively reverse these stimulatory effects of Ric-8A on Gαi1 nucleotide binding and GTPase activity. This observation correlates with findings that show RGS14 and Ric-8A share an overlapping binding region within the last 11 amino acids of Gαi1. As further evidence that these proteins are functionally linked, native RGS14 and Ric-8A coexist within the same hippocampal neurons. These findings demonstrate that RGS14 is a newly appreciated integrator of unconventional Ric-8A and Gαi1 signaling.

Predictably irrational: assaying cognitive inflexibility in mouse models of schizophrenia

The development of sophisticated, translatable mouse-based assays modeling the behavioral manifestations of neuropsychiatric diseases, such as schizophrenia, has lagged the advances in molecular and genomic techniques. Our laboratory has made efforts to fill this gap by investing in the development of novel assays, including adapting a touchscreen-based method for measuring cognitive and executive functions for use in mice. As part of these efforts, a recent study by Brigman et al. (2009) investigated the effects of subchronic phencyclidine treatment on mouse touchscreen-based pairwise visual discrimination and reversal learning. Here, we summarize the results of that study, and place them in the larger context of ongoing efforts to develop valid mouse "models" of schizophrenia, with a focus on reversal learning and other measures of cognitive flexibility. Touchscreen-based systems could provide a tractable platform for fully utilizing the mouse to elucidate the pathophysiology of cognitive inflexibility in schizophrenia and other neuropsychiatric disorders.

Genome-wide expression profiling of placentas in the p57Kip2 model of pre-eclampsia

Pre-eclampsia affects 6-10% of pregnancies and is one of the primary causes of premature birth. It is widely accepted that inappropriate placental development, combined with environmental factors, plays a major role in disease pathogenesis. The p57(Kip2) mouse is the only mouse model of pre-eclampsia that recapitulates the full spectrum of symptoms of the human disease, including placental abnormalities, hypertension, proteinuria and premature labour. In addition, pregnant females expressing wild-type levels of p57(Kip2) develop pre-eclampsia when carrying fetuses that lack p57(Kip2) expression. This demonstrates that either the fetus or the placenta causes the disease. Here, taking advantage of the unique genetics of the p57(Kip2) mouse, we have used full genome expression profiling to define the placental aspect of the p57(Kip2) phenotype at a molecular level and to conduct an unbiased search for factors involved in pre-eclampsia pathogenesis. During this analysis, we found that although mutant embryos demonstrate altered placental architecture and have histological changes indicative of reduced utero-placental blood flow, the p57(Kip2) pregnant females do not demonstrate hypertension or renal pathology. This suggests a model in which placental abnormalities cause pre-eclampsia only given other environmental variables. On the basis of this model, we expect that misregulation of molecular factors, while not able to cause a full spectrum of disease symptoms in this context, still occurs in these p57(Kip2) mutant mice. Our studies suggest a role for environmental factors in the p57(Kip2) pre-eclampsia phenotype and have identified several candidates for pre-eclampsia predisposition in this model, including known regulators of blood pressure, inflammation and apoptosis.