Animal Evolution: Looking for the First Nervous System

SummaryThe human brain is easily the most baffling bit of biology on the planet. How did the nervous system evolve? What came first: neurons or synaptic proteins? A new paper studying the pancake-shaped Trichoplax suggests it was not the neurons

Nano-fEM: Protein localization using photo-activated localization microscopy and electron microscopy

pre-printMapping the distribution of proteins is essential for understanding the function of proteins in a cell. Fluorescence microscopy is extensively used for protein localization, but subcellular context is often absent in fluorescence images. Immuno-electron microscopy, on the other hand, can localize proteins, but the technique is limited by a lack of compatible antibodies, poor preservation of morphology and because most antigens are not exposed to the specimen surface. Correlative approaches can acquire the fluorescence image from a whole cell first, either from immunofluorescence or genetically tagged proteins. The sample is then fixed and embedded for electron microscopy, and the images are correlated 1-3. However, the low-resolution fluorescence image and the lack of fiducial markers preclude the precise localization of proteins

Molecular basis of synaptic vesicle cargo recognition by the endocytic sorting adaptor stonin 2

Journal ArticleSynaptic transmission depends on clathrin-mediated recycling of synaptic vesicles (SVs). How select SV proteins are targeted for internalization has remained elusive. Stonins are evolutionarily conserved adaptors dedicated to endocytic sorting of the SV protein synaptotagmin. Our data identify the molecular determinants for recognition of synaptotagmin by stonin 2 or its Caenorhabditis elegans orthologue UNC-41B

Axon regeneration genes identified by RNAi screening in C. elegans

pre-printAxons of the mammalian CNS lose the ability to regenerate soon after development due to both an inhibitory CNS environment and the loss of cell-intrinsic factors necessary for regeneration. The complex molecular events required for robust regeneration of mature neurons are not fully understood, particularly in vivo. To identify genes affecting axon regeneration in Caenorhabditis elegans, we performed both an RNAi-based screen for defective motor axon regeneration in unc-70/-spectrin mutants and a candidate gene screen. From these screens, we identified at least 50 conserved genes with growth-promoting or growth-inhibiting functions. Through our analysis of mutants, we shed new light on certain aspects of regeneration, including the role of-B-spectrin and membrane dynamics, the antagonistic activity of MAP kinase signaling pathways, and the role of stress in promoting axon regeneration. Many gene candidates had not previously been associated with axon regeneration and implicate new pathways of interest for therapeutic intervention

CAPS and syntaxin dock dense core vesicles to the plasma membrane in neurons

Journal ArticleDocking to the plasma membrane prepares vesicles for rapid release. Here, we describe a mechanism for dense core vesicle docking in neurons. In Caenorhabditis elegons motor neurons, dense core vesicles dock at the plasma membrane but are excluded from active zones at synapses

Open syntaxin docks synaptic vesicles

Journal ArticleSynaptic vesicles dock to the plasma membrane at synapses to facilitate rapid exocytosis. Docking was originally proposed to require the soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) proteins; however, perturbation studies suggested that docking was independent of the SNARE proteins

Protein localization in electron micrographs using fluorescence nanoscopy

Journal ArticleA complete portrait of a cell requires a detailed description of its molecular topography: proteins must be linked to particular organelles. Immuno-electron microscopy can reveal locations of proteins with nanometer resolution but is limited by the quality of fixation, the paucity of antibodies, and the inaccessibility of the antigens. Here, we describe a method for correlative fluorescence electron microscopy (fEM) for the localization of proteins in electron micrographs. Proteins tagged with Citrine or tdEos were expressed in Caenorhabditis elegans, fixed and embedded. Tagged proteins were imaged from ultrathin sections using stimulated emission depletion microscopy (STED) or photoactivated localization microscopy (PALM). Fluorescence was correlated with organelles imaged in electron micrographs from the same sections. These methods were used to successfully localize histones, a mitochondrial protein, and a presynaptic dense projection protein in electron micrographs

Neural plasticity

Journal ArticleNeural plasticity refers to functional changes in the nervous system and therefore encompasses a range of phenomena from changes at synapses observed on a microscopic scale to changes in behavior observed in the whole animal. These diverse phenomena are related since changes in synapses are believed to underlie changes in an animal's behavior (Greenough and Bailey 1988)

Mutations in β-spectrin disrupt axon outgrowth and sarcomere structure

Journal ArticleB-Spectrin is a major component of the membrane skeleton, a structure found at the plasma membrane of most animal cells. B-Spectrin and the membrane skeleton have been proposed to stabilize cell membranes, generate cell polarity, or localize specific membrane proteins. We demonstrate that the Caenorhabditis elegans homologue of B-spectrin is encoded by the unc-70 gene. unc-70 null mutants develop slowly, and the adults are paralyzed and dumpy

Caenorhabditis elegans gene unc-25 encodes glutamic acid decarboxylase and is required for synaptic transmission but not synaptic development

Journal ArticleThe neurotransmitter GABA has been proposed to play a role during nervous system development. We show that the Caenorhabditis elegans gene unc-25 encodes glutamic acid decarboxylase (GAD), the GABA biosynthetic enzyme. unc-25 is expressed specifically in GABAergic neurons. Null mutations in unc-25 eliminate the UNC-25 protein or alter amino acids conserved in all known GADs, result in a complete lack of GABA, and cause defects in all GABA-mediated behaviors