Synaptic Ras GTPase-activating protein 1, also known as synaptic Ras-GAP 1 or SYNGAP1, is a protein that in humans is encoded by the SYNGAP1gene.[1][2][3] SYNGAP1 is a ras GTPase-activating protein that is critical for the development of cognition and proper synapse function. Mutations in humans can cause intellectual disability or epilepsy.
SynGAP1 is a complex protein with several functions that may be regulated temporally via complex isoforms.[4] A well-documented function of SynGAP1 involves NMDA receptor-mediated synaptic plasticity and membrane insertion of AMPA receptors through the suppression of upstream signaling pathways.[5] However, SynGAP1 has also been shown to function cooperatively with Unc51.1 in axon formation.[6] One way SynGAP1 affects these processes is through the MAP kinase signaling pathway by attenuation of Ras signalling.[7] However, alternative splicing and multiple translational start sites have been shown to cause opposing effects, illustrating the importance of multiple functional domains that reside within the c- and n-termini. For example, the expression of an α1 or α2 c-terminal variant of SynGAP1 will either increase or decrease synaptic strength, respectively.[4] Overall, SynGAP1 is essential for development and survival, which is evident as knockout mice die perinatally.[8]
Dendritic spine development and maturation
SynGAP1 is shown to localize at the postsynaptic density on the dendritic spines of excitatory synapses.[2] Cultured neurons of SynGAP heterozygotic and homozygotic knockout mice display accelerated maturation of dendritic spines, including an increase in overall spine size, which produces more mushroom shaped and less stubby spines.[5][7][9] Spine heads are enlarged due to the increased phosphorylation of cofilin, leading to a decrease in F-actin severing and turnover.[10] The increased size of the dendritic spines also corresponded to an increase in membrane bound AMPARs or a decrease in silent synapses. These neurons displayed a higher frequency and larger amplitudes of miniature excitatory postsynaptic potentials (mEPSP).[9] Mice models with domain specific mutations led to neonatal hyperactivity of the hippocampal trisynaptic circuit. Mutations had the greatest impact during the first 3 weeks of development, and reversal of mutations in adults did not improve behavior and cognition.[5]
Clinical significance
Several mutations in the SYNGAP1 gene were identified as the cause of intellectual disability. Intellectual disability is sometimes associated with syndromes of other defects caused by the same gene, but SYNGAP1-associated intellectual disability is not; it is therefore called non-syndromic intellectual disability. Since neither of the parents of children with this condition have the mutation, this means it was a sporadic mutation that occurred during division of the parents' gametes (meiosis) or fertilization of the egg. It is a dominant mutation, which means that the individual will be developmentally disabled even if only one allele is mutated.[11]
Mutations in this gene have also been found associated to cases of epileptic encephalopathies. (doi: 10.1038/ng.2646)
↑ 2.02.12.2Kim JH, Liao D, Lau LF, Huganir RL (Apr 1998). "SynGAP: a synaptic RasGAP that associates with the PSD-95/SAP90 protein family". Neuron. 20 (4): 683–91. doi:10.1016/S0896-6273(00)81008-9. PMID9581761.
↑Kim JH, Lee HK, Takamiya K, Huganir RL (Feb 2003). "The role of synaptic GTPase-activating protein in neuronal development and synaptic plasticity". The Journal of Neuroscience. 23 (4): 1119–24. PMID12598599.
↑ 9.09.1Vazquez LE, Chen HJ, Sokolova I, Knuesel I, Kennedy MB (Oct 2004). "SynGAP regulates spine formation". The Journal of Neuroscience. 24 (40): 8862–72. doi:10.1523/jneurosci.3213-04.2004. PMID15470153.
↑Hamdan FF, Gauthier J, Spiegelman D, Noreau A, Yang Y, Pellerin S, Dobrzeniecka S, Côté M, Perreau-Linck E, Perreault-Linck E, Carmant L, D'Anjou G, Fombonne E, Addington AM, Rapoport JL, Delisi LE, Krebs MO, Mouaffak F, Joober R, Mottron L, Drapeau P, Marineau C, Lafrenière RG, Lacaille JC, Rouleau GA, Michaud JL (Feb 2009). "Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation". The New England Journal of Medicine. 360 (6): 599–605. doi:10.1056/NEJMoa0805392. PMC2925262. PMID19196676.
Further reading
Fantl WJ, Escobedo JA, Martin GA, Turck CW, del Rosario M, McCormick F, Williams LT (May 1992). "Distinct phosphotyrosines on a growth factor receptor bind to specific molecules that mediate different signaling pathways". Cell. 69 (3): 413–23. doi:10.1016/0092-8674(92)90444-H. PMID1374684.
Kroll J, Waltenberger J (Dec 1997). "The vascular endothelial growth factor receptor KDR activates multiple signal transduction pathways in porcine aortic endothelial cells". The Journal of Biological Chemistry. 272 (51): 32521–7. doi:10.1074/jbc.272.51.32521. PMID9405464.
Kim JH, Liao D, Lau LF, Huganir RL (Apr 1998). "SynGAP: a synaptic RasGAP that associates with the PSD-95/SAP90 protein family". Neuron. 20 (4): 683–91. doi:10.1016/S0896-6273(00)81008-9. PMID9581761.
Chen HJ, Rojas-Soto M, Oguni A, Kennedy MB (May 1998). "A synaptic Ras-GTPase activating protein (p135 SynGAP) inhibited by CaM kinase II". Neuron. 20 (5): 895–904. doi:10.1016/S0896-6273(00)80471-7. PMID9620694.
Husi H, Ward MA, Choudhary JS, Blackstock WP, Grant SG (Jul 2000). "Proteomic analysis of NMDA receptor-adhesion protein signaling complexes". Nature Neuroscience. 3 (7): 661–9. doi:10.1038/76615. PMID10862698.
Li W, Okano A, Tian QB, Nakayama K, Furihata T, Nawa H, Suzuki T (Jun 2001). "Characterization of a novel synGAP isoform, synGAP-beta". The Journal of Biological Chemistry. 276 (24): 21417–24. doi:10.1074/jbc.M010744200. PMID11278737.
Pei L, Teves RL, Wallace MC, Gurd JW (Aug 2001). "Transient cerebral ischemia increases tyrosine phosphorylation of the synaptic RAS-GTPase activating protein, SynGAP". Journal of Cerebral Blood Flow and Metabolism. 21 (8): 955–63. doi:10.1097/00004647-200108000-00008. PMID11487731.
Nagase T, Kikuno R, Ohara O (Aug 2001). "Prediction of the coding sequences of unidentified human genes. XXI. The complete sequences of 60 new cDNA clones from brain which code for large proteins". DNA Research. 8 (4): 179–87. doi:10.1093/dnares/8.4.179. PMID11572484.
Yi J, Kloeker S, Jensen CC, Bockholt S, Honda H, Hirai H, Beckerle MC (Mar 2002). "Members of the Zyxin family of LIM proteins interact with members of the p130Cas family of signal transducers". The Journal of Biological Chemistry. 277 (11): 9580–9. doi:10.1074/jbc.M106922200. PMID11782456.
Song B, Meng F, Yan X, Guo J, Zhang G (Oct 2003). "Cerebral ischemia immediately increases serine phosphorylation of the synaptic RAS-GTPase activating protein SynGAP by calcium/calmodulin-dependent protein kinase II alpha in hippocampus of rats". Neuroscience Letters. 349 (3): 183–6. doi:10.1016/S0304-3940(03)00830-9. PMID12951199.
Oh JS, Manzerra P, Kennedy MB (Apr 2004). "Regulation of the neuron-specific Ras GTPase-activating protein, synGAP, by Ca2+/calmodulin-dependent protein kinase II". The Journal of Biological Chemistry. 279 (17): 17980–8. doi:10.1074/jbc.M314109200. PMID14970204.
Song B, Yan XB, Zhang GY (Apr 2004). "PSD-95 promotes CaMKII-catalyzed serine phosphorylation of the synaptic RAS-GTPase activating protein SynGAP after transient brain ischemia in rat hippocampus". Brain Research. 1005 (1–2): 44–50. doi:10.1016/j.brainres.2004.01.032. PMID15044063.
Brandenberger R, Wei H, Zhang S, Lei S, Murage J, Fisk GJ, Li Y, Xu C, Fang R, Guegler K, Rao MS, Mandalam R, Lebkowski J, Stanton LW (Jun 2004). "Transcriptome characterization elucidates signaling networks that control human ES cell growth and differentiation". Nature Biotechnology. 22 (6): 707–16. doi:10.1038/nbt971. PMID15146197.
Jaffe H, Vinade L, Dosemeci A (Aug 2004). "Identification of novel phosphorylation sites on postsynaptic density proteins". Biochemical and Biophysical Research Communications. 321 (1): 210–8. doi:10.1016/j.bbrc.2004.06.122. PMID15358237.