Gephyrin and the postsynaptic GABAergic complex

Although gephyrin is an important postsynaptic scaffolding protein at GABAergic synapses, the role of gephyrin for GABAergic synapse formation and/or maintenance is still under debate. In order to address this question, I manipulated the gephyrin expression levels by using small hairpin RNAs (shRNAs) to decrease gephyrin expression, by overexpressing a gephyrin-EGFP fusion protein to decrease the gephyrin clustering and by overexpression of wild type gephyrin in cultured hippocampal pyramidal cells to detect their effects on synapses. I found that decreased postsynaptic gephyrin clustering led to not only decreased postsynaptic GABA(A) receptor clusters but also decreased GABAergic innervation. It is concluded that gephyrin plays a critical role for the stability of GABAergic synapses. ^ Further more, I showed that altering the levels of expression/clustering of gephyrin also affects glutamatergic synapses. Decreasing gephyrin clusters led to increased size but not density of both the postsynaptic glutamatergic PSD-95 clusters and the presynaptic glutamatergic terminals contacting the pyramidal cells. Overexpression of gephyrin led to a slight decrease in size but not in density of both PSD-95 clusters and presynaptic glutamatergic terminals. However, the size or density of the glutamate GluR1-AMPA, or NR1-NMDA receptor clusters was not affected. It is concluded that the expression and clustering of gephyrin, a postsynaptic GABAergic scaffold protein, also plays a role in the control of the size of glutamatergic contacts. ^ I also showed that GRIP1c4-7 is a short splice form of GRIP1a, present in rat genome. The N-terminal sequence specifies its membrane localization. GRIP1c4-7 and GRIP1a/b interact with gephyrin by co-precipitation from rat brain extracts and from extracts of HEK293 cells. Moreover, purified gephyrin binds to purified GRIP1c4-7 or GRIP1a/b as shown by an affinity pull down assay, indicating that these molecules directly interact with each other. Postsynaptic gephyrin clusters colocalized with GRIP1c4-7 and GRIP1a/b clusters in cultured hippocampal neurons. These results indicate that GRIP1 proteins could be involved in the trafficking and recycling of postsynaptic gephyrin at GABAergic synapses. ^ By using gamma2-GABAAR shRNAs, an approach which is different from the knockout mice, we have shown that gamma2 subunit is important for the clustering of beta2/3-GABAARs and gephyrin. More importantly, we have shown that disrupting normal postsynaptic gamma2-GABAAR clustering leads to a significant reduction in the GABAergic innervation. The studies were done in cultured hippocampal pyramidal cells. I further extended the research to in vivo studies by transfecting neurons with in utero electroporation where I found that decreased GABA(A)R clustering and GABAergic innervation of pyramidal neurons in the post-natal rat cerebral cortex after in utero transfection of these neurons with the gamma2 shRNAs. All these results support the hypothesis that γ2 subunit is essential for the postsynaptic clustering of the GABAAR and the postsynaptic clustering of GABAAR is essential for the stability of the GABAergic synapses. ^ All these studies put together show: (I) gephyrin is critical for the postsynaptic clustering of many GABAARs; (II) γ2-GABA AR clustering is critical for the postsynaptic clustering of gephyrin and (III) the postsynaptic clustering of GABAAR and gephryin is cirtical for the stability of the presynaptic GABAergic innervation.

Gephyrin and the postsynaptic GABAergic complex

Although gephyrin is an important postsynaptic scaffolding protein at GABAergic synapses, the role of gephyrin for GABAergic synapse formation and/or maintenance is still under debate. In order to address this question, I manipulated the gephyrin expression levels by using small hairpin RNAs (shRNAs) to decrease gephyrin expression, by overexpressing a gephyrin-EGFP fusion protein to decrease the gephyrin clustering and by overexpression of wild type gephyrin in cultured hippocampal pyramidal cells to detect their effects on synapses. I found that decreased postsynaptic gephyrin clustering led to not only decreased postsynaptic GABA(A) receptor clusters but also decreased GABAergic innervation. It is concluded that gephyrin plays a critical role for the stability of GABAergic synapses. ^ Further more, I showed that altering the levels of expression/clustering of gephyrin also affects glutamatergic synapses. Decreasing gephyrin clusters led to increased size but not density of both the postsynaptic glutamatergic PSD-95 clusters and the presynaptic glutamatergic terminals contacting the pyramidal cells. Overexpression of gephyrin led to a slight decrease in size but not in density of both PSD-95 clusters and presynaptic glutamatergic terminals. However, the size or density of the glutamate GluR1-AMPA, or NR1-NMDA receptor clusters was not affected. It is concluded that the expression and clustering of gephyrin, a postsynaptic GABAergic scaffold protein, also plays a role in the control of the size of glutamatergic contacts. ^ I also showed that GRIP1c4-7 is a short splice form of GRIP1a, present in rat genome. The N-terminal sequence specifies its membrane localization. GRIP1c4-7 and GRIP1a/b interact with gephyrin by co-precipitation from rat brain extracts and from extracts of HEK293 cells. Moreover, purified gephyrin binds to purified GRIP1c4-7 or GRIP1a/b as shown by an affinity pull down assay, indicating that these molecules directly interact with each other. Postsynaptic gephyrin clusters colocalized with GRIP1c4-7 and GRIP1a/b clusters in cultured hippocampal neurons. These results indicate that GRIP1 proteins could be involved in the trafficking and recycling of postsynaptic gephyrin at GABAergic synapses. ^ By using gamma2-GABAAR shRNAs, an approach which is different from the knockout mice, we have shown that gamma2 subunit is important for the clustering of beta2/3-GABAARs and gephyrin. More importantly, we have shown that disrupting normal postsynaptic gamma2-GABAAR clustering leads to a significant reduction in the GABAergic innervation. The studies were done in cultured hippocampal pyramidal cells. I further extended the research to in vivo studies by transfecting neurons with in utero electroporation where I found that decreased GABA(A)R clustering and GABAergic innervation of pyramidal neurons in the post-natal rat cerebral cortex after in utero transfection of these neurons with the gamma2 shRNAs. All these results support the hypothesis that γ2 subunit is essential for the postsynaptic clustering of the GABAAR and the postsynaptic clustering of GABAAR is essential for the stability of the GABAergic synapses. ^ All these studies put together show: (I) gephyrin is critical for the postsynaptic clustering of many GABAARs; (II) γ2-GABA AR clustering is critical for the postsynaptic clustering of gephyrin and (III) the postsynaptic clustering of GABAAR and gephryin is cirtical for the stability of the presynaptic GABAergic innervation.

The Plant Nucleoskeleton: Ultrastructural Organization and Identification of NuMA Homologues in the Nuclear Matrix and Mitotic Spindle of Plant Cells

In the present work we investigate the structural organization of the nucleoskeleton ofAllium cepameristematic root cells. Resinless sections reveal for the first time a residual filamentous network in plant nuclei. This network is composed of branched knobbed filaments with associated globular structures, connected to the lamina and to the dense aggregates of different sizes. Results of immunoblotting show that many components of this network are homologues of intermediate filament-type proteins. NuMA, a coiled-coil protein related to intermediate filaments, found in animal cells, can also be detected in this plant nuclear matrix system. Immunofluorescence reveals a diffuse distribution of the animal NuMA homologues in plant nuclear core filaments in interphase. Resinless immunoelectron microscopy further reveals a distribution along the extended filaments and the dense aggregates. During mitosis, in contrast to the accumulation at the poles in animal cells, NuMA homologues in plant onion cells show a diffuse pattern, which may correspond to the spindle matrix. Our data are the first report of the conservation in plants of NuMA proteins, which may be involved in both nuclear and mitotic spindle organizations.This work has been supported by the Spanish DGES (ProjectsPB95-0117 and PB96-0909). The Spanish Agency of Co-operation(AECI) through the Spanish-Chinese Intergovernmental Agreementhas financed Dr. W. Yu.Peer reviewe

Phospho-dependent ubiquitination and degradation of PAR-1 regulates synaptic morphology and tau-mediated Aβ toxicity in Drosophila

The conserved kinases PAR-1/MARK are critically involved in processes such as asymmetric cell division, cell polarity and neuronal differentiation. Their deregulation has been implicated in diseases including Alzheimer's disease and cancer. Given the importance of PAR-1/MARK in health and disease, their activities need to be tightly controlled. However, little is known about the molecular mechanisms underlying their regulation in vivo. Here we show that in Drosophila, a phosphorylation-dependent ubiquitination mechanism restrains PAR-1 activation. Active PAR-1 generated by LKB1-controlled phosphorylation is targeted for ubiquitination and degradation by SCF (Skp, Cullin, F-box containing complex) (Slimb), whose action is antagonized by the deubiquitinating enzyme fat facets. This newly identified PAR-1-modifying module critically regulates synaptic morphology and tau-mediated postsynaptic toxicity of amyloid precursor protein (APP)/Aβ-42, the causative agents of Alzheimer's disease, at the Drosophila neuromuscular junction. Our results provide new insights into the regulation of PAR-1 in various physiological processes and offer new therapeutic strategies for diseases involving PAR-1/MARK deregulation

Spontaneous and light-induced photon emission from intact brains of chick embryos

Photon emission (PE) and light-induced photon emission(LPE) of intact brains isolated from chick embryos have been measured by using the single photon counting device. Experimental results showed that the intensity level of photon emission was detected to be higher from intact brain than from the medium in which the brain was immerged during measuring, and the emission intensity was related to the developmental stages, the healthy situation of the measured embryos, and the freshness of isolated brains as well. After white light illumination, a short-life delayed emission from intact brains was observed, and its relaxation behavior followed a hyperbolic rather than an exponential law. According to the hypothesis of biophoton emission originating from a delocalized coherent electromagnetic field and Frohlich’ s idea of coherent long-range interactions in biological systems, discussions were made on the significance of photon emission in studying cell communication, biological regulation, living system’s relevance to its environment, and also on the relations between the detected photon emission and the coherent electromagnetic field. The detected photon emission should be comprehended in the manner of the interactions between the intrinsic fields within the living systems and their environmental external fields

Gephyrin clustering is required for the stability of GABAergic synapses

Although gephyrin is an important postsynaptic scaffolding protein at GABAergic synapses, the role of gephyrin for GABAergic synapse formation and/or maintenance is still under debate. We report here that knocking down gephyrin expression with small hairpin RNAs (shRNAs) in cultured hippocampal pyramidal cells decreased both the number of gephyrin and GABA(A) receptor clusters. Similar results were obtained by disrupting the clustering of endogenous gephyrin by overexpressing a gephyrin-EGFP fusion protein that formed aggregates with the endogenous gephyrin. Disrupting postsynaptic gephyrin clusters also had transsynaptic effects leading to a significant reduction of GABAergic presynaptic boutons contacting the transfected pyramidal cells. Consistent with the morphological decrease of GABAergic synapses, electrophysiological analysis revealed a significant reduction in both the amplitude and frequency of the spontaneous inhibitory postsynaptic currents (sIPSCs). However, no change in the whole-cell GABA currents was detected, suggesting a selective effect of gephyrin on GABA(A) receptor clustering at postsynaptic sites. It is concluded that gephyrin plays a critical role for the stability of GABAergic synapses