Dystroglycan Adds More Sugars to the Midline Cocktail

In this issue of Neuron, Wright et al. (2012) identify two novel mediators of α-dystroglycan glycosylation in mouse and unravel a novel function of glycosylated dystroglycan in axon guidance by providing evidence for direct binding of α-DG to the midline chemorepellent Slit2

Robo3-Driven Axon Midline Crossing Conditions Functional Maturation of a Large Commissural Synapse

SummaryDuring the formation of neuronal circuits, axon pathfinding decisions specify the location of synapses on the correct brain side and in correct target areas. We investigated a possible link between axon midline crossing and the subsequent development of output synapses formed by these axons. Conditional knockout of Robo3 in the auditory system forced a large commissural synapse, the calyx of Held, to be exclusively formed on the wrong, ipsilateral side. Ipsilateral calyx of Held synapses showed strong transmission defects, with reduced and desynchronized transmitter release, fewer fast-releasable vesicles, and smaller and more variable presynaptic Ca2+ currents. Transmission defects were not observed in a downstream inhibitory synapse, and some defects persisted into adulthood. These results suggest that axon midline crossing conditions functional maturation of commissural synapses, thereby minimizing the impact of mislocalized synapses on information processing. This mechanism might be relevant to human disease caused by mutations in the ROBO3 gene

Adult Mouse Subventricular Zone Stem and Progenitor Cells Are Sessile and Epidermal Growth Factor Receptor Negatively Regulates Neuroblast Migration

Background: The adult subventricular zone (SVZ) contains stem and progenitor cells that generate neuroblasts throughout life. Although it is well accepted that SVZ neuroblasts are migratory, recent evidence suggests their progenitor cells may also exhibit motility. Since stem and progenitor cells are proliferative and multipotential, if they were also able to move would have important implications for SVZ neurogenesis and its potential for repair. Methodology/Principal Findings: We studied whether SVZ stem and/or progenitor cells are motile in transgenic GFP+ slices with two photon time lapse microscopy and post hoc immunohistochemistry. We found that stem and progenitor cells; mGFAP-GFP+ cells, bright nestin-GFP+ cells and Mash1+ cells were stationary in the SVZ and rostral migratory stream (RMS). In our search for motile progenitor cells, we uncovered a population of motile bIII-tubulin+ neuroblasts that expressed low levels of epidermal growth factor receptor (EGFr). This was intriguing since EGFr drives proliferation in the SVZ and affects migration in other systems. Thus we examined the potential role of EGFr in modulating SVZ migration. Interestingly, EGFr low neuroblasts moved slower and in more tortuous patterns than EGFr-negative neuroblasts. We next questioned whether EGFr stimulation affects SVZ cell migration by imaging Gad65-GFP+ neuroblasts in the presence of transforming growth factor alpha (TGF-a), an EGFr-selective agonist. Indeed, acute exposure to TGF-a decreased the percentage of motile cells by approximately 40%

Roles of db-cAMP, IBMX and RA in Aspects of Neural Differentiation of Cord Blood Derived Mesenchymal-Like Stem Cells

Mesenchymal stem cells (MSCs) have multilineage differentiation potential which includes cell lineages of the central nervous system; hence MSCs might be useful in the treatment of neurodegenerative diseases such as Parkinson's disease. Although mesenchymal stem cells have been shown to differentiate into the neural lineage, there is still little knowledge about the underlying mechanisms of differentiation particularly towards specialized neurons such as dopaminergic neurons. Here, we show that MSCs derived from human umbilical cord blood (MSChUCBs) are capable of expressing tyrosine hydroxylase (TH) and Nurr1, markers typically associated with DA neurons. We also found differential phosphorylation of TH isoforms indicating the presence of post-translational mechanisms possibly activating and modifying TH in MSChUCB. Furthermore, functional dissection of components in the differentiation medium revealed that dibutyryl-cAMP (db-cAMP), 3-isobutyl-1-methylxanthine (IBMX) and retinoic acid (RA) are involved in the regulation of Nurr1 and Neurofilament-L expression as well as in the differential phosphorylation of TH. We also demonstrate a possible inhibitory role of the protein kinase A signaling pathway in the phosphorylation of specific TH isoforms

Delayed Onset of Experimental Autoimmune Encephalomyelitis in Olig1 Deficient Mice

BACKGROUND: Olig1 is a basic helix-loop-helix (bHLH) transcription factor that is essential for oligodendrogenesis and efficient remyelination. However, its role in neurodegenerative disorders has not been well-elucidated. METHODOLOGY/PRINCIPAL FINDINGS: Here we investigated the effects of Olig1 deficiency on experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). We show that the mean disease onset of myelin oligodendrocyte glycoprotein (MOG)-induced EAE in Olig1(-/-) mice is significantly slower than wide-type (WT) mice (19.8 ± 2.2 in Olig1(-/-) mice and 9.5 ± 0.3 days in WT mice). In addition, 10% of Olig1(-/-) mice did not develop EAE by the end of the observation periods (60 days). The severity of EAE, the extent of demyelination, and the activation of microglial cells and astrocytes in spinal cords, were significantly milder in Olig1(-/-) mice compared with WT mice in the early stage. Moreover, the visual function, as assessed by the second-kernel of multifocal electroretinograms, was better preserved, and the number of degenerating axons in the optic nerve was significantly reduced in Olig1(-/-) mice. Interestingly, Olig1 deficiency had no effect on T cell response capability, however, it reduced the expression of myelin proteins such as MOG, myelin basic protein (MBP) and myelin-associated glycoprotein (MAG). The expression of Olig2 remained unchanged in the optic nerve and brain, and it was reduced in the spinal cord of Olig1(-/-) mice. CONCLUSIONS/SIGNIFICANCE: Our results suggest that the Olig1 signaling pathways may be involved in the incidence rate and the severity of neurological symptoms in MS

A New Role for TIMP-1 in Modulating Neurite Outgrowth and Morphology of Cortical Neurons

BACKGROUND:Tissue inhibitor of metalloproteinases-1 (TIMP-1) displays pleiotropic activities, both dependent and independent of its inhibitory activity on matrix metalloproteinases (MMPs). In the central nervous system (CNS), TIMP-1 is strongly upregulated in reactive astrocytes and cortical neurons following excitotoxic/inflammatory stimuli, but no information exists on its effects on growth and morphology of cortical neurons. PRINCIPAL FINDINGS:We found that 24 h incubation with recombinant TIMP-1 induced a 35% reduction in neurite length and significantly increased growth cones size and the number of F-actin rich microprocesses. TIMP-1 mediated reduction in neurite length affected both dendrites and axons after 48 h treatment. The effects on neurite length and morphology were not elicited by a mutated form of TIMP-1 inactive against MMP-1, -2 and -3, and still inhibitory for MMP-9, but were mimicked by a broad spectrum MMP inhibitor. MMP-9 was poorly expressed in developing cortical neurons, unlike MMP-2 which was present in growth cones and whose selective inhibition caused neurite length reductions similar to those induced by TIMP-1. Moreover, TIMP-1 mediated changes in cytoskeleton reorganisation were not accompanied by modifications in the expression levels of actin, betaIII-tubulin, or microtubule assembly regulatory protein MAP2c. Transfection-mediated overexpression of TIMP-1 dramatically reduced neuritic arbour extension in the absence of detectable levels of released extracellular TIMP-1. CONCLUSIONS:Altogether, TIMP-1 emerges as a modulator of neuronal outgrowth and morphology in a paracrine and autrocrine manner through the inhibition, at least in part, of MMP-2 and not MMP-9. These findings may help us understand the role of the MMP/TIMP system in post-lesion pre-scarring conditions

Shared and differential features of Robo3 expression pattern in amniotes

In Bilaterians, commissural neurons project their axons across the midline of the nervous system to target neurons on the opposite side. In mammals, midline crossing at the level of the hindbrain and spinal cord requires the Robo3 receptor which is transiently expressed by all commissural neurons. Unlike other Robo receptors, mammalian Robo3 receptors do not bind Slit ligands and promote midline crossing. Surprisingly, not much is known about Robo3 distribution and mechanism of action in other vertebrate species. Here, we have use whole-mount immunostaining, tissue clearing and light-sheet fluorescent microscopy to study Robo3 expression pattern in multiple embryonic tissue from diverse representatives of amniotes at distinct stages, including squamate (African house snake), birds (chicken, duck, pigeon, ostrich, emu and zebra finch), early postnatal marsupial mammals (fat-tailed dunnart), and eutherian mammals (mouse and human). The analysis of this rich and unique repertoire of amniote specimen reveals conserved features of Robo3 expression in midbrain, hindbrain and spinal cord commissural circuits, which together with subtle but meaningful modifications could account for species-specific evolution of sensory-motor and cognitive capacities. Our results also highlight important differences of precerebellar nuclei development across amniotes. This article is protected by copyright. All rights reserved

Development of the neurons controlling fertility in humans: new insights from 3D imaging and transparent fetal brains

Fertility in mammals is controlled by hypothalamic neurons that secrete gonadotropin-releasing hormone (GnRH). These neurons differentiate in the olfactory placodes during embryogenesis and migrate from the nose to the hypothalamus before birth. Information regarding this process in humans is sparse. Here, we adapted new tissue-clearing and whole-mount immunohistochemical techniques to entire human embryos/fetuses to meticulously study this system during the first trimester of gestation in the largest series of human fetuses examined to date. Combining these cutting-edge techniques with conventional immunohistochemistry, we provide the first chronological and quantitative analysis of GnRH neuron origins, differentiation and migration, as well as a 3D atlas of their distribution in the fetal brain. We reveal not only that the number of GnRH-immunoreactive neurons in humans is significantly higher than previously thought, but that GnRH cells migrate into several extrahypothalamic brain regions in addition to the hypothalamus. Their presence in these areas raises the possibility that GnRH has non-reproductive roles, creating new avenues for research on GnRH functions in cognitive, behavioral and physiological processes