The major cell classes of the brain differ in their developmental processes, metabolism, signaling, and function To better understand the functions and interactions of the cell types that comprise these classes, we acutely purified representative populations of neurons, astrocytes, oligodendrocyte precursor cells, newly formed oligodendrocytes, myelinating oligodendrocytes, microglia, endothelial cells, and pericytes from mouse cerebral cortex We generated a transcriptome database for these eight cell types by RNA sequencing and used a sensitive algorithm to detect alternative splicing events in each cell type Bioinformatic analyses identified thousands of new cell type-enriched genes and splicing isoforms that will provide novel markers for cell identification, tools for genetic manipulation, and insights into the biology of the brain For example, our data provide clues as to how neurons and astrocytes differ in their ability to dynamically regulate glycolytic flux and lactate generation attributable to unique splicing of PKM2, the gene encoding the glycolytic enzyme pyruvate kinase This dataset will provide a powerful new resource for understanding the development and function of the brain To ensure the widespread distribution of these datasets, we have created a user-friendly website (http://webstanfordedu/group/barres_lab/brain_rnaseqhtml) that provides a platform for analyzing and comparing transciption and alternative splicing profiles for various cell classes in the brain

https://www.jneurosci.org/content/jneuro/34/36/11929.full.pdf

An RNA-Sequencing Transcriptome and Splicing Database of Glia, Neurons, and Vascular Cells of the Cerebral Cortex

Neuronal growth cones navigate over long distances along specific pathways to find their correct targets. The mechanisms and molecules that direct this pathfinding are the topics of this review. Growth cones appear to be guided by at least four different mechanisms: contact attraction, chemoattraction, contact repulsion, and chemorepulsion. Evidence is accumulating that these mechanisms act simultaneously and in a coordinated manner to direct pathfinding and that they are mediated by mechanistically and evolutionarily conserved ligand-receptor systems.

The Molecular Biology of Axon Guidance

After injury to the adult central nervous system (CNS), injured axons cannot regenerate past the lesion. In this review, we present evidence that this is due to the formation of a glial scar. Chondroitin and keratan sulphate proteoglycans are among the main inhibitory extracellular matrix molecules that are produced by reactive astrocytes in the glial scar, and they are believed to play a crucial part in regeneration failure. We will focus on this role, as well as considering the behaviour of regenerating neurons in the environment of CNS injury.

/pdf/regeneration-beyond-the-glial-scar-tnk3lt4e77.pdf

Regeneration beyond the glial scar

Endocytic mechanisms control the lipid and protein composition of the plasma membrane, thereby regulating how cells interact with their environments. Here, we review what is known about mammalian endocytic mechanisms, with focus on the cellular proteins that control these events. We discuss the well-studied clathrin-mediated endocytic mechanisms and dissect endocytic pathways that proceed independently of clathrin. These clathrin-independent pathways include the CLIC/GEEC endocytic pathway, arf6-dependent endocytosis, flotillin-dependent endocytosis, macropinocytosis, circular doral ruffles, phagocytosis, and trans-endocytosis. We also critically review the role of caveolae and caveolin1 in endocytosis. We highlight the roles of lipids, membrane curvature-modulating proteins, small G proteins, actin, and dynamin in endocytic pathways. We discuss the functional relevance of distinct endocytic pathways and emphasize the importance of studying these pathways to understand human disease processes.

Mechanisms of Endocytosis

Conserved signaling pathways that activate the mitogen-activated protein kinases (MAPKs) are involved in relaying extracellular stimulations to intracellular responses. The MAPKs coordinately regulate cell proliferation, differentiation, motility, and survival, which are functions also known to be mediated by members of a growing family of MAPK-activated protein kinases (MKs; formerly known as MAPKAP kinases). The MKs are related serine/threonine kinases that respond to mitogenic and stress stimuli through proline-directed phosphorylation and activation of the kinase domain by extracellular signal-regulated kinases 1 and 2 and p38 MAPKs. There are currently 11 vertebrate MKs in five subfamilies based on primary sequence homology: the ribosomal S6 kinases, the mitogen- and stress-activated kinases, the MAPK-interacting kinases, MAPK-activated protein kinases 2 and 3, and MK5. In the last 5 years, several MK substrates have been identified, which has helped tremendously to identify the biological role of the members of this family. Together with data from the study of MK-knockout mice, the identities of the MK substrates indicate that they play important roles in diverse biological processes, including mRNA translation, cell proliferation and survival, and the nuclear genomic response to mitogens and cellular stresses. In this article, we review the existing data on the MKs and discuss their physiological functions based on recent discoveries.

/pdf/erk-and-p38-mapk-activated-protein-kinases-a-family-of-xi88207cal.pdf

Erk and p38 mapk-activated protein kinases: a family of protein kinases with diverse biological functions

Sulfated proteoglycans in astroglial barriers inhibit neurite outgrowth in vitro

This invention relates, e.g., to a method for promoting CNS axon regeneration, comprising (1) inhibiting the expression or activity in a neuron of one or more of the members of the Kruppel-like transcription factor (KLF) family that suppress axon growth (e.g., KLF 1, 2, 3, 4, 5, 9, 12, 13, 14, 15 and/or 16), and/or (2) stimulating the expression or activity in a neuron of one or more of the members of the KLF family that promote axon growth (e.g., KLF 6 and/or 7).

/pdf/klf-family-members-regulate-intrinsic-axon-regeneration-3sgzssid9n.pdf

Klf family members regulate intrinsic axon regeneration ability

Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow.

/pdf/microtubule-stabilization-reduces-scarring-and-causes-axon-19yw2yvfjo.pdf

Microtubule Stabilization Reduces Scarring and Causes Axon Regeneration After Spinal Cord Injury

The 8D9 antigen, a cell surface protein isolated from chicken brain that is related to the L1 class of cell adhesion molecules, is shown to contain an activity that promotes the attachment of neurons and the outgrowth of neurites from chicken tecta and mouse cerebellum. When purified 8D9 antigen is attached to a nitrocellulose-coated substrate, neurons rapidly attach and extend unfasciculated neurites. Little or no attachment of astroglia, oligodendroglia, and fibroblast-like cells to the 8D9 antigen is observed. We propose that a function of the 8D9 antigen is that of a neurite extension-promoting substrate in axon fascicles and in regeneration of peripheral nerves.

https://www.pnas.org/content/pnas/84/21/7753.full.pdf

Vance Lemmon

Papers

Sulfated proteoglycans in astroglial barriers inhibit neurite outgrowth in vitro

Klf family members regulate intrinsic axon regeneration ability

Microtubule Stabilization Reduces Scarring and Causes Axon Regeneration After Spinal Cord Injury

An L1-like molecule, the 8D9 antigen, is a potent substrate for neurite extension.

L1-mediated axon outgrowth occurs via a homophilic binding mechanism