Toriyama, M. et al. Shootin1: a protein involved in the organization of an asymmetric signal for neuronal polarization. J. Cell Biol. 175, 147-157

Division of Signal Transduction, Nara Institute of Science and Technology, Ikoma 630-0192, Japan.
The Journal of Cell Biology (Impact Factor: 9.83). 11/2006; 175(1):147-57. DOI: 10.1083/jcb.200604160
Source: PubMed

ABSTRACT Neurons have the remarkable ability to polarize even in symmetrical in vitro environments. Although recent studies have shown that asymmetric intracellular signals can induce neuronal polarization, it remains unclear how these polarized signals are organized without asymmetric cues. We describe a novel protein, named shootin1, that became up-regulated during polarization of hippocampal neurons and began fluctuating accumulation among multiple neurites. Eventually, shootin1 accumulated asymmetrically in a single neurite, which led to axon induction for polarization. Disturbing the asymmetric organization of shootin1 by excess shootin1 disrupted polarization, whereas repressing shootin1 expression inhibited polarization. Overexpression and RNA interference data suggest that shootin1 is required for spatially localized phosphoinositide-3-kinase activity. Shootin1 was transported anterogradely to the growth cones and diffused back to the soma; inhibiting this transport prevented its asymmetric accumulation in neurons. We propose that shootin1 is involved in the generation of internal asymmetric signals required for neuronal polarization.

Download full-text


Available from: Tadayuki Shimada, Aug 27, 2014
20 Reads
  • Source
    • "The polarization of neurons is essential for the proper wiring of the nervous system, and abnormal polarization is associated with several neuropsychiatric diseases, including schizophrenia [6] and autism [7], [8]. The precise mechanism of this neuronal symmetry breaking remains an open question, but several pathways in the process have recently been elucidated [9]–[15]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: As neurons develop, several immature processes (i.e., neurites) grow out of the cell body. Over time, each neuron breaks symmetry when only one of its neurites grows much longer than the rest, becoming an axon. This symmetry breaking is an important step in neurodevelopment, and aberrant symmetry breaking is associated with several neuropsychiatric diseases, including schizophrenia and autism. However, the effects of neurite count in neuronal symmetry breaking have never been studied. Existing models for neuronal polarization disagree: some predict that neurons with more neurites polarize up to several days later than neurons with fewer neurites, while others predict that neurons with different neurite counts polarize synchronously. We experimentally find that neurons with different neurite counts polarize synchronously. We also show that despite the significant differences among the previously proposed models, they all agree with our experimental findings when the expression levels of the proteins responsible for symmetry breaking increase with neurite count. Consistent with these results, we observe that the expression levels of two of these proteins, HRas and shootin1, significantly correlate with neurite count. This coordinated symmetry breaking we observed among neurons with different neurite counts may be important for synchronized polarization of neurons in developing organisms.
    PLoS ONE 02/2013; 8(2):e54905. DOI:10.1371/journal.pone.0054905 · 3.23 Impact Factor
  • Source
    • "To our knowledge, there is no optimal vector system available which has a regulation component dependent on disease-severity along with heart muscle-specific gene expression [19]. Therefore, we sought to create a heart-failure-specific gene therapy system using the B-type natriuretic peptide (BNP) promoter [20], RNA polymerase II-mediated short hairpin RNA (shRNA) [21] and an AAV serotype 9 (AAV9) vector [22]. As BNP expression level is reported to be a most reliable marker of disease severity [23] in heart failure, and its basal expression level is quite low in normal hearts and practically negligible in other organs, BNP promoter activity may afford control over therapeutic gene expression in both a disease-severity-dependent- and heart-muscle-specific manner. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The targeting of Ca(2+) cycling has emerged as a potential therapy for the treatment of severe heart failure. These approaches include gene therapy directed at overexpressing sarcoplasmic reticulum (SR) Ca(2+) ATPase, or ablation of phospholamban (PLN) and associated protein phosphatase 1 (PP1) protein complexes. We previously reported that PP1β, one of the PP1 catalytic subunits, predominantly suppresses Ca(2+) uptake in the SR among the three PP1 isoforms, thereby contributing to Ca(2+) downregulation in failing hearts. In the present study, we investigated whether heart-failure-inducible PP1β-inhibition by adeno-associated viral-9 (AAV9) vector mediated gene therapy is beneficial for preventing disease progression in genetic cardiomyopathic mice. We created an adeno-associated virus 9 (AAV9) vector encoding PP1β short-hairpin RNA (shRNA) or negative control (NC) shRNA. A heart failure inducible gene expression system was employed using the B-type natriuretic protein (BNP) promoter conjugated to emerald-green fluorescence protein (EmGFP) and the shRNA sequence. AAV9 vectors (AAV9-BNP-EmGFP-PP1βshRNA and AAV9-BNP-EmGFP-NCshRNA) were injected into the tail vein (2×10(11) GC/mouse) of muscle LIM protein deficient mice (MLPKO), followed by serial analysis of echocardiography, hemodynamic measurement, biochemical and histological analysis at 3 months. In the MLPKO mice, BNP promoter activity was shown to be increased by detecting both EmGFP expression and the induced reduction of PP1β by 25% in the myocardium. Inducible PP1βshRNA delivery preferentially ameliorated left ventricular diastolic function and mitigated adverse ventricular remodeling. PLN phosphorylation was significantly augmented in the AAV9-BNP-EmGFP-PP1βshRNA injected hearts compared with the AAV9-BNP-EmGFP-NCshRNA group. Furthermore, BNP production was reduced, and cardiac interstitial fibrosis was abrogated at 3 months. Heart failure-inducible molecular targeting of PP1β has potential as a novel therapeutic strategy for heart failure.
    PLoS ONE 04/2012; 7(4):e35875. DOI:10.1371/journal.pone.0035875 · 3.23 Impact Factor
  • Source
    • "The rule of one axon and multiple dendrites still operates under the restriction that the Sema3A-exposed neurite could not become the axon. Spontaneous axon formation away from the Sema3A may depend on stochastic local elevation of cAMP/PKA (Shelly et al., 2007) and local activation and accumulation of putative axon determinants (Shi et al., 2003; Yoshimura et al., 2005; Jacobson et al., 2006; Toriyama et al., 2006; Shelly et al., 2007), amplified by local autocatalytic process. The accompanying long-range suppression of cAMP (Shelly et al., 2010) would further ensure the low cAMP level (and the reciprocal high cGMP level) and the dendrite differentiation of the Sema3A-exposed neurite. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Semaphorin 3A (Sema3A) is a secreted factor known to guide axon/dendrite growth and neuronal migration. We found that it also acts as a polarizing factor for axon/dendrite development in cultured hippocampal neurons. Exposure of the undifferentiated neurite to localized Sema3A suppressed its differentiation into axon and promoted dendrite formation, resulting in axon formation away from the Sema3A source, and bath application of Sema3A to polarized neurons promoted dendrite growth but suppressed axon growth. Fluorescence resonance energy transfer (FRET) imaging showed that Sema3A elevated the cGMP but reduced cAMP and protein kinase A (PKA) activity, and its axon suppression is attributed to the downregulation of PKA-dependent phosphorylation of axon determinants LKB1 and GSK-3β. Downregulating Sema3A signaling in rat embryonic cortical progenitors via in utero electroporation of siRNAs against the Sema3A receptor neuropilin-1 also resulted in polarization defects in vivo. Thus, Sema3A regulates the earliest step of neuronal morphogenesis by polarizing axon/dendrite formation.
    Neuron 08/2011; 71(3):433-46. DOI:10.1016/j.neuron.2011.06.041 · 15.05 Impact Factor
Show more