Dendritic morphology determines many aspects of neuronal function, including action potential propagation and information processing. However, the question remains as to how distinct neuronal dendrite branching patterns are established. Here, we report that postsynaptic density-95 (PSD-95), a protein involved in dendritic spine maturation and clustering of synaptic signaling proteins, plays a novel role in regulating dendrite outgrowth and branching, independent of its synaptic functions. In immature neurons, overexpression of PSD-95 decreases the proportion of primary dendrites that undergo additional branching, resulting in a marked reduction of secondary dendrite number. Conversely, knocking down PSD-95 protein in immature neurons increases secondary dendrite number. The effect of PSD-95 is activity-independent and is antagonized by cypin, a nonsynaptic protein that regulates PSD-95 localization. Binding of cypin to PSD-95 correlates with formation of stable dendrite branches. Finally, overexpression of PSD-95 in COS-7 cells disrupts microtubule organization, indicating that PSD-95 may modulate microtubules to regulate dendritic branching. Whereas many factors have been identified which regulate dendrite number, our findings provide direct evidence that proteins primarily involved in synaptic functions can also play developmental roles in shaping how a neuron patterns its dendrite branches.

An interdependent relationship between the vascular and nervous systems begins during the earliest stages of development and persists through the mammalian lifespan. Accordingly, the process of adult neurogenesis involves the coordinated response of both systems to maintain a specialized microenvironment (niche) that tips the scale towards maintenance or regeneration, as needed. Understanding the nature and regulation of this balance will provide a foundation on which the potential for molecular-and stem cell-based therapies can be developed to treat prevalent CNS diseases and disorders. The vasculature is cited as a prominent feature within the adult subventricular zone and subgranular zone, known adult neural stem cell niches, helping to retain neural stem and progenitor cell potential. The vascular compartment within the neural stem cell niche has the unique opportunity to not only regulate neural stem and progenitor cells through direct contact with, and paracrine signaling from, endothelial and mural cells that make up blood vessels, but also integrates systemic signals into the local microenvironment via distribution of soluble factors from blood circulation to regulate stem cell niche behavior. Understanding the intricate role that the vasculature plays to influence neural stem cells in the context of niche regulation will help to bridge the gap from bench to bedside for the development of regeneration-based therapies for the CNS. Keywords adult neural stem cell; endothelial-derived factors; vascular endotheliumOnly recently has the discovery of adult neurogenesis overturned the long-standing dogma describing the adult mammalian brain as a static organ. With the discoveries of postnatal neurogenesis and the existence of adult neural stem cells (NSCs) [1][2][3][4], a field once limited by the postnatal 'static brain' model is now breaking ground at a rapid pace. Although well characterized within the developing embryo, the concept of adult neurogenesis is still relatively new, gaining attention and capturing the interest of biologists and clinicians. The possible therapeutic benefits of treating neurological disorders and disease via adult stem cell-based therapies represent an open door to novel approaches and treatments. However, to truly harness the therapeutic potential of stem cell-based therapies, a solid understanding of the intrinsic and extrinsic mechanisms surrounding NSC regulation needs to be met.

Fundamental to understanding how tissues function is understanding how the cells that compose them communicate. In most tissues and organs, cells do not exist as homotypic monolayers but rather coexist as multiple different cell types in close proximity to one another. In some cases, these relationships are random and have no functional significance; others are symbiotic, where the presence and proximity of a neighboring cell are vital to another cell's quiescence, specification, maturation, function, survival, and so on. Although biochemical, genetic, genomic, and proteomic methods have revealed a wealth of molecules known to participate in cell signaling pathways, many such signaling networks have been established using in vitro systems, and thus it is still unclear how cells within a threedimensional (3D), functional tissue environment use these pathways.This question and the increasing importance of 3D microenvironments in cancer (Håkanson et al. 2011) and stem cell biology (Doetsch et al. 1997;Shen et al. 2008;Tavazoie et al. 2008;Kazanis et al. 2010) SummaryIntercellular signaling is a fundamental requirement for complex biological system function and survival. Communication between adjoining cells is largely achieved via gap junction channels made up of multiple subunits of connexin proteins, each with unique selectivity and regulatory properties. Intercellular communication via gap junction channels facilitates transmission of an array of cellular signals, including ions, macromolecules, and metabolites that coordinate physiological processes throughout tissues and entire organisms. Although current methods used to quantify connexin expression rely on number or area density measurements in a field of view, they lack cellular assignment, distance measurement capabilities (both within the cell and to extracellular structures), and complete automation. We devised an automated computational approach built on a contour expansion algorithm platform that allows connexin protein detection and assignment to specific cells within complex tissues. In addition, parallel implementation of the contour expansion algorithm allows for high-throughput analysis as the complexity of the biological sample increases. This method does not depend specifically on connexin identification and can be applied more widely to the analysis of numerous immunocytochemical markers as well as to identify particles within tissues such as nanoparticles, gene delivery vehicles, or even cellular fragments such as exosomes or microparticles. (J Histochem Cytochem 61:283-293, 2013)