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Gene expression regulation by C. elegans SAM-10

ABSTRACT: Little is known about transcriptional control of neurite branching or presynaptic differentiation, events that occur relatively late in neuronal development. Using the C. elegans mechanosensory circuit as an in vivo model, we show that SAM-10, an ortholog of mammalian Single-Stranded DNA binding Protein (SSDP), functions cell-autonomously in the nucleus to regulate synaptic differentiation as well as positioning of a single neurite branch. PLM mechanosensory neurons in sam-10 mutants exhibit abnormal placement of the neurite branch point, and defective synaptogenesis, characterized by an overextended synaptic varicosity, underdeveloped synaptic morphology and disrupted co-localization of active zone and synaptic vesicles. SAM-10 functions coordinately with LDB-1 (Lim Domain Binding protein-1), demonstrated by our observations that 1) mutations in either gene show similar defects in PLM neurons; and 2) LDB-1 is required for SAM-10 nuclear localization. SAM-10 regulates PLM synaptic differentiation by suppressing transcription of prk-2, which encodes an ortholog of the mammalian Pim kinase family. PRK-2-mediated activities of SAM-10 are specifically involved in PLM synaptic differentiation, but not other sam-10 phenotypes such as neurite branching. Thus, these data reveal a novel transcriptional signaling pathway that regulates neuronal specification of neurite branching and presynaptic differentiation.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE25285 | GEO | 2010/11/12

SECONDARY ACCESSION(S): PRJNA134831

REPOSITORIES: GEO

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Project description:Little is known about transcriptional control of neurite branching or presynaptic differentiation, events that occur relatively late in neuronal development. Using the C. elegans mechanosensory circuit as an in vivo model, we show that SAM-10, an ortholog of mammalian Single-Stranded DNA binding Protein (SSDP), functions cell-autonomously in the nucleus to regulate synaptic differentiation as well as positioning of a single neurite branch. PLM mechanosensory neurons in sam-10 mutants exhibit abnormal placement of the neurite branch point, and defective synaptogenesis, characterized by an overextended synaptic varicosity, underdeveloped synaptic morphology and disrupted co-localization of active zone and synaptic vesicles. SAM-10 functions coordinately with LDB-1 (Lim Domain Binding protein-1), demonstrated by our observations that 1) mutations in either gene show similar defects in PLM neurons; and 2) LDB-1 is required for SAM-10 nuclear localization. SAM-10 regulates PLM synaptic differentiation by suppressing transcription of prk-2, which encodes an ortholog of the mammalian Pim kinase family. PRK-2-mediated activities of SAM-10 are specifically involved in PLM synaptic differentiation, but not other sam-10 phenotypes such as neurite branching. Thus, these data reveal a novel transcriptional signaling pathway that regulates neuronal specification of neurite branching and presynaptic differentiation. Animals were grown on fresh 8P plates (Wormbook.org) until gravid. Eggs were collected by bleaching and hatched in M9 buffer overnight. L1 animals were fed on fresh food for 2 hours at room temperature, harvested and separated from worm debris using a 25μm mesh. RNA was isolated using a standard Trizol protocol. RNA preps were stored at -80C. Quality of RNA preps was first estimated using Agilent 2100 Bioanalyzer. RNA was then reverse-transcribed using the Genisphere Array 350 kit, which generate tagged cDNA. Resulted products are hybridized to the microarrays. Four independent high quality RNA preps (RIN>=7) were chosen for microarray assay using long oligomer-based spotted microarray (Washington University, St. Louis, MO). For dye-swap controls, we ran a technical replicate hybridization for each pair of samples in which the dyes are reversed. Gene spots with “found/good” signals (defined by ScanArray, channel flag 3) in all scans were chosen for gene expression analysis.

Project description:This is a model of one presynaptic and one postsynaptic cell, as described in the article: Gamma oscillation by synaptic inhibition in a hippocampal interneuronal network model. Wang XJ, Buzsáki G. J Neurosci. 1996 Oct 15;16(20):6402-13. PMID:8815919; Abstract: Fast neuronal oscillations (gamma, 20-80 Hz) have been observed in the neocortex and hippocampus during behavioral arousal. Using computer simulations, we investigated the hypothesis that such rhythmic activity can emerge in a random network of interconnected GABAergic fast-spiking interneurons. Specific conditions for the population synchronization, on properties of single cells and the circuit, were identified. These include the following: (1) that the amplitude of spike afterhyperpolarization be above the GABAA synaptic reversal potential; (2) that the ratio between the synaptic decay time constant and the oscillation period be sufficiently large; (3) that the effects of heterogeneities be modest because of a steep frequency-current relationship of fast-spiking neurons. Furthermore, using a population coherence measure, based on coincident firings of neural pairs, it is demonstrated that large-scale network synchronization requires a critical (minimal) average number of synaptic contacts per cell, which is not sensitive to the network size. By changing the GABAA synaptic maximal conductance, synaptic decay time constant, or the mean external excitatory drive to the network, the neuronal firing frequencies were gradually and monotonically varied. By contrast, the network synchronization was found to be high only within a frequency band coinciding with the gamma (20-80 Hz) range. We conclude that the GABAA synaptic transmission provides a suitable mechanism for synchronized gamma oscillations in a sparsely connected network of fast-spiking interneurons. In turn, the interneuronal network can presumably maintain subthreshold oscillations in principal cell populations and serve to synchronize discharges of spatially distributed neurons. The presynaptic and postsynaptic cell have identical parameters and the variables in each cell are identified by using _pre or _post as a postfix to their names. The presynaptic cell influences the postsynaptic one via the synapse (variables and parameters: I_syn, E_syn, g_syn, F, theta_syn, alpha, beta). The applied current to the presynaptic cell, I_app_pre, is set to 2 microA/cm2 for 10 ms as in figure 1C of the article. The dependence of the postsynaptic cell on directly applied current can be investigated in isolation by setting I_app_pre to 0 and altering I_app_post. Originally created by libAntimony v1.4 (using libSBML 3.4.1)

Project description:The prevailing model behind synapse development and specificity is that a multitude of adhesion molecules engage in transsynaptic interactions to induce pre- and post-synaptic assembly. How these extracellular interactions translate into intracellular signal transduction for synaptic assembly remains unclear. One such complex formed by immunoglobulin superfamily member 21 (IgSF21) and neurexin2α regulates GABAergic synapse development in the mouse brain, but the precise molecular mechanisms underlying this activity remain unclear. Here, we reveal that the interaction between presynaptic Nrxn2α and postsynaptic IgSF21 is a high-affinity receptor-ligand interaction and identify a binding interface in the IgSF21-Nrxn2α complex. Despite being expressed in both dendritic and somatic regions, IgSF21 preferentially regulates dendritic GABAergic presynaptic differentiation whereas another canonical Nrxn ligand, neuroligin2 (Nlgn2), regulates primarily perisomatic presynaptic differentiation. To explore mechanisms that could underly this compartment specificity, we targeted multiple signaling pathways pharmacologically while monitoring the synaptogenic activity of IgSF21 and Nlgn2. Interestingly, both IgSF21 and Nlgn2 require c-jun N-terminal kinase (JNK)-mediated signaling, whereas Nlgn2, but not IgSF21, additionally requires CaMKII and Src kinase activity. JNK inhibition diminished de novo presynaptic differentiation without affecting the maintenance of formed synapses. We further found that Nrxn2α knockout brains exhibit altered synaptic JNK activity in a sex-specific fashion, suggesting functional linkage between Nrxns and JNK in vivo. Thus, our study elucidates the structural and functional relationship of IgSF21 with Nrxn2α and distinct signaling pathways for IgSF21 and Nlgn downstream of Nrxn2α. We therefore propose a revised hypothesis that Nrxns act as molecular hubs to specify synaptic properties not only through their multiple extracellular ligands but also through distinct intracellular signaling pathways of these ligands.

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Gene expression regulation by C. elegans SAM-10

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