Project description:One of the biggest challenges in biology is to understand how activity at the cellular level of neurons, as a result of their mutual interactions, leads to the observed behavior of an organism responding to a variety of environmental stimuli. Investigating the intermediate or mesoscopic level of organization in the nervous system is a vital step towards understanding how the integration of micro-level dynamics results in macro-level functioning. The coordination of many different co-occurring processes at this level underlies the command and control of overall network activity. In this paper, we have considered the somatic nervous system of the nematode Caenorhabditis elegans, for which the entire neuronal connectivity diagram is known. We focus on the organization of the system into modules, i.e., neuronal groups having relatively higher connection density compared to that of the overall network. We show that this mesoscopic feature cannot be explained exclusively in terms of considerations such as, optimizing for resource constraints (viz., total wiring cost) and communication efficiency (i.e., network path length). Even including information about the genetic relatedness of the cells cannot account for the observed modular structure. Comparison with other complex networks designed for efficient transport (of signals or resources) implies that neuronal networks form a distinct class. This suggests that the principal function of the network, viz., processing of sensory information resulting in appropriate motor response, may be playing a vital role in determining the connection topology. Using modular spectral analysis we make explicit the intimate relation between function and structure in the nervous system. This is further brought out by identifying functionally critical neurons purely on the basis of patterns of intra- and inter-modular connections. Our study reveals how the design of the nervous system reflects several constraints, including its key functional role as a processor of information.

Project description:Background: With its fully sequenced genome and simple, well-defined nervous system, the nematode C. elegans offers a unique opportunity to correlate gene expression with neuronal differentiation. The lineal origin, cellular morphology and synaptic connectivity of each of the 302 neurons are known. In many instances, specific behaviors can be attributed to particular neurons or circuits. Here we describe microarray-based methods that monitor gene expression in C. elegans neurons and thereby link comprehensive profiles of neuronal transcription to key developmental and functional attributes of the nervous system. Results: We employed complementary microarray-based strategies to profile gene expression in the embryonic and larval nervous systems. In the MAPCeL (Micro-Array Profiling C. elegans Cells) method, we used Fluorescence Activated Cell Sorting (FACS) to isolate GFP-tagged embryonic neurons for microarray analysis. To profile the larval nervous system, we used the mRNA-tagging technique in which an epitope-labeled mRNA binding protein (FLAG-PAB-1) was transgenically expressed in neurons for immunoprecipitation of cell-specific transcripts. These combined approaches identified approximately 2,500 mRNAs that are highly enriched in either the embryonic or larval C. elegans nervous system. These data are validated in part by the detection of gene classes (e.g. transcription factors, ion channels, synaptic vesicle components) with established roles in neuronal development or function. In addition to utilizing these profiling approaches to define stage specific gene expression, we also applied the mRNA-tagging method to fingerprint a specific neuron type, the A-class group of cholinergic motor neurons, during early larval development. A comparison of these data to a MAPCeL profile of embryonic A-class motor neurons identified genes with common functions in both types of A-class motor neurons as well as transcripts with roles specific to each motor neuron type. Conclusion: We describe microarray-based strategies for generating expression profiles of embryonic and larval C. elegans neurons. These methods can be applied to particular neurons at specific developmental stages and therefore provide an unprecedented opportunity to obtain spatially and temporally defined snapshots of gene expression in a simple model nervous system. Keywords: nervous system, development

Project description:Background: With its fully sequenced genome and simple, well-defined nervous system, the nematode C. elegans offers a unique opportunity to correlate gene expression with neuronal differentiation. The lineal origin, cellular morphology and synaptic connectivity of each of the 302 neurons are known. In many instances, specific behaviors can be attributed to particular neurons or circuits. Here we describe microarray-based methods that monitor gene expression in C. elegans neurons and thereby link comprehensive profiles of neuronal transcription to key developmental and functional attributes of the nervous system. Results: We employed complementary microarray-based strategies to profile gene expression in the embryonic and larval nervous systems. In the MAPCeL (Micro-Array Profiling C. elegans Cells) method, we used Fluorescence Activated Cell Sorting (FACS) to isolate GFP-tagged embryonic neurons for microarray analysis. To profile the larval nervous system, we used the mRNA-tagging technique in which an epitope-labeled mRNA binding protein (FLAG-PAB-1) was transgenically expressed in neurons for immunoprecipitation of cell-specific transcripts. These combined approaches identified approximately 2,500 mRNAs that are highly enriched in either the embryonic or larval C. elegans nervous system. These data are validated in part by the detection of gene classes (e.g. transcription factors, ion channels, synaptic vesicle components) with established roles in neuronal development or function. In addition to utilizing these profiling approaches to define stage specific gene expression, we also applied the mRNA-tagging method to fingerprint a specific neuron type, the A-class group of cholinergic motor neurons, during early larval development. A comparison of these data to a MAPCeL profile of embryonic A-class motor neurons identified genes with common functions in both types of A-class motor neurons as well as transcripts with roles specific to each motor neuron type. Conclusion: We describe microarray-based strategies for generating expression profiles of embryonic and larval C. elegans neurons. These methods can be applied to particular neurons at specific developmental stages and therefore provide an unprecedented opportunity to obtain spatially and temporally defined snapshots of gene expression in a simple model nervous system. Experiment Overall Design: Our goal is to profile gene expression throughout the nervous system of the model organism Caenorhabditis elegans. As a first goal, we profiled the entire nervous system at two developmental timepoints. To isolate transcripts from embryonic neurons we employed the MAPCeL (Microarray Profiling C. elegans Cells) technique in which pan-neuronal GFP+ cells are captured by FACS for RNA isolation. Since postembryonic cells are unattainable via this method, we used mRNA-tagging to isolated pan-neural RNAs from larval animals. In short, an epitope tagged poly-A binding protein (FLAG-PAB-1) was driven in all neurons using the F25B3.3 promoter. Following formaldehyde cross-linking, animals were passed through a French press and Dounce homogenized to isolate a cell-free extract. Anti-FLAG antibodies were incubated with the cell-free extract to capture FLAG-PAB bound RNAs. After elution and reversal of the crosslinks, RNAs are isolated by TriZOL extraction. We also identified transcripts enriched in a subset of C. elegans larval neurons, the A-class neurons (using unc-4::3xFLAG::PAB-1). Experiment Overall Design: 3 sets of experiments normalized separately by RMA Experiment Overall Design: larval references of sets 2 and 3 originate from the same hybridizations (accompanying CEL files are identical)

Dataset Information

Visualizing the organization and differentiation of the male-specific nervous system of C. elegans.

Publications

Visualizing the organization and differentiation of the male-specific nervous system of C. elegans.

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