Development of the mammalian axial skeleton requires signaling through the G i subfamily of heterotrimeric G proteins

Laboratory of Neurobiology, National Institute of Environmental Health Sciences, National Institutes of Health/Department of Health and Human Services, Durham, NC 27709.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2012; 109(52). DOI: 10.1073/pnas.1219810110
Source: PubMed


129/SvEv mice with a loss-of-function mutation in the heterotrimeric G protein α-subunit gene Gnai3 have fusions of ribs and lumbar vertebrae, indicating a requirement for Gα(i) (the "inhibitory" class of α-subunits) in somite derivatives. Mice with mutations of Gnai1 or Gnai2 have neither defect, but loss of both Gnai3 and one of the other two genes increases the number and severity of rib fusions without affecting the lumbar fusions. No myotome defects are observed in Gnai3/Gnai1 double-mutant embryos, and crosses with a conditional allele of Gnai2 indicate that Gα(i) is specifically required in cartilage precursors. Penetrance and expressivity of the rib fusion phenotype is altered in mice with a mixed C57BL/6 × 129/SvEv genetic background. These phenotypes reveal a previously unknown role for G protein-coupled signaling pathways in development of the axial skeleton.

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    • "Furthermore with this approach an up regulation of the remaining isoform may be prevented. Whereas an appropriate Gαi2-model is available [13] the corresponding Gαi3-mouse model has not been created so far. "
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    ABSTRACT: G-protein-coupled receptors (GPCRs) are the most abundant receptors in the heart and therefore are common targets for cardiovascular therapeutics. The activated GPCRs transduce their signals via heterotrimeric G-proteins. The four major families of G-proteins identified so far are specified through their α-subunit: Gαi, Gαs, Gαq and G12/13. Gαi-proteins have been reported to protect hearts from ischemia reperfusion injury. However, determining the individual impact of Gαi2 or Gαi3 on myocardial ischemia injury has not been clarified yet. Here, we first investigated expression of Gαi2 and Gαi3 on transcriptional level by quantitative PCR and on protein level by immunoblot analysis as well as by immunofluorescence in cardiac tissues of wild-type, Gαi2-, and Gαi3-deficient mice. Gαi2 was expressed at higher levels than Gαi3 in murine hearts, and irrespective of the isoform being knocked out we observed an up regulation of the remaining Gαi-protein. Myocardial ischemia promptly regulated cardiac mRNA and with a slight delay protein levels of both Gαi2 and Gαi3, indicating important roles for both Gαi isoforms. Furthermore, ischemia reperfusion injury in Gαi2- and Gαi3-deficient mice exhibited opposite outcomes. Whereas the absence of Gαi2 significantly increased the infarct size in the heart, the absence of Gαi3 or the concomitant upregulation of Gαi2 dramatically reduced cardiac infarction. In conclusion, we demonstrate for the first time that the genetic ablation of Gαi proteins has protective or deleterious effects on cardiac ischemia reperfusion injury depending on the isoform being absent.
    PLoS ONE 05/2014; 9(5):e98325. DOI:10.1371/journal.pone.0098325 · 3.23 Impact Factor
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    • "Second, they reveal a critical requirement for the G-γ5 subtype in the second wave of cardiac development contributing to the formation of the right ventricle and outflow tract. Since the cardiac defects resulting from loss of the G-γ5 subtype are much more severe than individual or combinatorial disruption of any of the G-α subtypes [17]–[21], these results suggest a separate requirement for G-βγ5 signaling above and beyond that of any G-α pathway in this process. Although the mechanism is still being investigated, we hypothesize that G-βγ5 signaling may represent a point of convergence for G-protein-coupled, integrin, and fibroblast growth factor receptor signaling pathways that are critical for the expansion or survival of cardiac progenitor cells within the second heart field. "
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    ABSTRACT: Heterotrimeric G-proteins modulate many processes essential for embryonic development including cellular proliferation, migration, differentiation, and survival. Although most research has focused on identifying the roles of the various αsubtypes, there is growing recognition that similarly divergent βγ dimers also regulate these processes. In this paper, we show that targeted disruption of the mouse Gng5 gene encoding the γ5 subtype produces embryonic lethality associated with severe head and heart defects. Collectively, these results add to a growing body of data that identify critical roles for the γ subunits in directing the assembly of functionally distinct G-αβγ trimers that are responsible for regulating diverse biological processes. Specifically, the finding that loss of the G-γ5 subtype is associated with a reduced number of cardiac precursor cells not only provides a causal basis for the mouse phenotype but also raises the possibility that G-βγ5 dependent signaling contributes to the pathogenesis of human congenital heart problems.
    PLoS ONE 03/2014; 9(3):e90970. DOI:10.1371/journal.pone.0090970 · 3.23 Impact Factor
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    • "C57BL/6, and B6.SJL-Ptprca Pepcb/BoyJ mice were obtained from Jackson Laboratory. Gnai2fl/fl mice and Gnai3-/- mice on a mixed background have been described [6]. Both strains were each backcrossed 11 times on to C57BL/6. "
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    ABSTRACT: B lymphocytes are compartmentalized within lymphoid organs. The organization of these compartments depends upon signaling initiated by G-protein linked chemoattractant receptors. To address the importance of the G-proteins Gαi2 and Gαi3 in chemoattractant signaling we created mice lacking both proteins in their B lymphocytes. While bone marrow B cell development and egress is grossly intact; mucosal sites, splenic marginal zones, and lymph nodes essentially lack B cells. There is a partial block in splenic follicular B cell development and a 50-60% reduction in splenic B cells, yet normal numbers of splenic T cells. The absence of Gαi2 and Gαi3 in B cells profoundly disturbs the architecture of lymphoid organs with loss of B cell compartments in the spleen, thymus, lymph nodes, and gastrointestinal tract. This results in a severe disruption of B cell function and a hyper-IgM like syndrome. Beyond the pro-B cell stage, B cells are refractory to chemokine stimulation, and splenic B cells are poorly responsive to antigen receptor engagement. Gαi2 and Gαi3 are therefore critical for B cell chemoattractant receptor signaling and for normal B cell function. These mice provide a worst case scenario of the consequences of losing chemoattractant receptor signaling in B cells.
    PLoS ONE 08/2013; 8(8):e72596. DOI:10.1371/journal.pone.0072596 · 3.23 Impact Factor
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