Homeostatic processes are involved in the maintenance of unique neuronal phenotypes and circuit function in the face of plastic changes or injury. Neuronal homeostasis is a result of orchestrated activity of multiple gene products and, evidently, some of these can be neuron-specific. Here, we propose to use one of the best described """"""""simple"""""""" neural circuits, the pyloric central pattern generator (CPG) in the stomatogastric ganglion of the crab (Cancer borealis), to address how gene expression patterns differ across different neuron types and how changes in gene expression maintain circuit function in response to changes in activity and modulatory state. We will start with two synaptically coupled, unambiguously identifiable neuron types that are known to be crucial for the production of rhythmic motor patterns controlling foregut movements. We propose 2 conceptually overlapping aims that will lead to the unbiased genome-wide view of neuron identity and function:
Aim 1) Using sequencing-by-ligation &pyrosequencing platforms adapted to the single cell level, we will tag and quantify the majority of gene products expressed in both cholinergic (PD) and glutamatergic (LP) motoneurons, and identify which genes are differentially expressed between them, and which genes are relevant to neuronal excitability and rhythmic properties of the CPG circuit.
Aim 2) We will determine which genes are involved in homeostatic regulation and functional recovery of the stereotypic rhythmic properties of the circuit. The decentralization of the stomatogastric ganglion by deprivation of descending modulatory inputs results in silencing of pyloric motor activity. However, the isolated circuit is able to restore its excitability and rhythmic properties within 2-3 days. This recovery requires changes in gene expression that can be both cell-specific and """"""""universal"""""""". We will profile the gene expression patterns at different time points during circuit silencing and recovery of functional activity. As a result, we will identify candidate genes crucial for such functional rescue of the endogenous motor rhythms. We also hypothesize that there are evolutionarily conserved subsets of genes involved in these recovery/homeostatic mechanisms that can be shared between arthropods and mammals.
Here, we will characterize molecular mechanisms of how individual neurons maintain their specific properties and connections to meet the functional demands in a neural circuit controlling rhythmic foregut movements. Specifically we will describe homeostatic processes underlying functional recovery in a neural circuit following silencing and deprivation of modulatory inputs. Although we mainly develop these approaches in a model Cancer preparation where identifiable and experimentally accessible neurons allow such a proof of principle, the methods and related biological questions are of broad, general importance and their applicability to mammals will be tested as the project develops.
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