Nav2 is necessary for cranial nerve development and blood pressure regulation

Abstract Background All-trans retinoic acid (atRA) is required for nervous system development, including the developing hindbrain region. Neuron navigator 2 (Nav2) was first identified as an atRA-responsive gene in human neuroblastoma cells (retinoic acid-induced in neuroblastoma 1, Rainb1), and is required for atRA-mediated neurite outgrowth. In this paper, we explore the importance of Nav2 in nervous system development and function in vivo. Results Nav2 hypomorphic homozygous mutants show decreased survival starting at birth. Nav2 mutant embryos show an overall reduction in nerve fiber density, as well as specific defects in cranial nerves IX (glossopharyngeal) and X (vagus). Nav2 hypomorphic mutant adult mice also display a blunted baroreceptor response compared to wild-type controls. Conclusions Nav2 functions in mammalian nervous system development, and is required for normal cranial nerve development and blood pressure regulation in the adult

BACE2 distribution in major brain cell types and identification of novel substrates

β-Site APP-cleaving enzyme 1 (BACE1) inhibition is considered one of the most promising therapeutic strategies for Alzheimer's disease, but current BACE1 inhibitors also block BACE2. As the localization and function of BACE2 in the brain remain unknown, it is difficult to predict whether relevant side effects can be caused by off-target inhibition of BACE2 and whether it is important to generate BACE1-specific inhibitors. Here, we show that BACE2 is expressed in discrete subsets of neurons and glia throughout the adult mouse brain. We uncover four new substrates processed by BACE2 in cultured glia: vascular cell adhesion molecule 1, delta and notch-like epidermal growth factor-related receptor, fibroblast growth factor receptor 1, and plexin domain containing 2. Although these substrates were not prominently cleaved by BACE2 in healthy adult mice, proinflammatory TNF induced a drastic increase in BACE2-mediated shedding of vascular cell adhesion molecule 1 in CSF. Thus, although under steady-state conditions the effect of BACE2 cross-inhibition by BACE1-directed inhibitors is rather subtle, it is important to consider that side effects might become apparent under physiopathological conditions that induce TNF expression

Developmental expression of 4-repeat-Tau induces neuronal aneuploidy in Drosophila tauopathy models

Tau-mediated neurodegeneration in Alzheimer's disease and tauopathies is generally assumed to start in a normally developed brain. However, several lines of evidence suggest that impaired Tau isoform expression during development could affect mitosis and ploidy in post-mitotic differentiated tissue. Interestingly, the relative expression levels of Tau isoforms containing either 3 (3R-Tau) or 4 repeats (4R-Tau) play an important role both during brain development and neurodegeneration. Here, we used genetic and cellular tools to study the link between 3R and 4R-Tau isoform expression, mitotic progression in neuronal progenitors and post-mitotic neuronal survival. Our results illustrated that the severity of Tau-induced adult phenotypes depends on 4R-Tau isoform expression during development. As recently described, we observed a mitotic delay in 4R-Tau expressing cells of larval eye discs and brains. Live imaging revealed that the spindle undergoes a cycle of collapse and recovery before proceeding to anaphase. Furthermore, we found a high level of aneuploidy in post-mitotic differentiated tissue. Finally, we showed that overexpression of wild type and mutant 4R-Tau isoform in neuroblastoma SH-SY5Y cell lines is sufficient to induce monopolar spindles. Taken together, our results suggested that neurodegeneration could be in part linked to neuronal aneuploidy caused by 4R-Tau expression during brain development

Progressive leukoencephalopathy impairs neurobehavioral development in sialin-deficient mice

Slc17a5−/− mice represent an animal model for the infantile form of sialic acid storage disease (SASD). We analyzed genetic and histological time-course expression of myelin and oligodendrocyte (OL) lineage markers in different parts of the CNS, and related this to postnatal neurobehavioral development in these mice. Sialin-deficient mice display a distinct spatiotemporal pattern of sialic acid storage, CNS hypomyelination and leukoencephalopathy. Whereas few genes are differentially expressed in the perinatal stage (p0), microarray analysis revealed increased differential gene expression in later postnatal stages (p10–p18). This included progressive upregulation of neuroinflammatory genes, as well as continuous down-regulation of genes that encode myelin constituents and typical OL lineage markers. Age-related histopathological analysis indicates that initial myelination occurs normally in hindbrain regions, but progression to more frontal areas is affected in Slc17a5−/− mice. This course of progressive leukoencephalopathy and CNS hypomyelination delays neurobehavioral development in sialin-deficient mice. Slc17a5−/− mice successfully achieve early neurobehavioral milestones, but exhibit progressive delay of later-stage sensory and motor milestones. The present findings may contribute to further understanding of the processes of CNS myelination as well as help to develop therapeutic strategies for SASD and other myelination disorders

In vivo evidence for ligand-specific receptor activation in the central CRF system, as measured by local cerebral glucose utilization.

Corticotropin-releasing factor (CRF) is well known for its role in the hypothalamic-pituitary-adrenocortical (HPA) axis and its involvement in stress and anxiety. CRF acts via two main receptor subtypes, CRF(1) and CRF(2). Other endogenous CRF-related peptide ligands are the Urocortins 1 and 2 and Stresscopin. While CRF is thought to mediate its anxiogenic-like properties through CRF(1), the role of CRF(2) and its endogenous ligands Urocortin 2 and Stresscopin are less clear, with a suggested role in mediating the delayed effects of stress. Measurement of local cerebral glucose utilization (LCGU) provides an estimate of neuronal activity, and is of potential use as a translational tool in comparison to FDG PET. We hypothesized that comparison of the patterns of metabolic changes induced by CRF-related peptides could provide further information on their role in the brain. The present studies examined the effects of CRF-related peptides on LCGU, and the role of CRF(1) and CRF(2) in the CRF-induced LCGU response. CRF induced increases in LCGU in hypothalamic, thalamic, cerebellar and hippocampal regions, and further studies using antagonists or mutant mice lacking a functional CRF(1) receptor clearly suggested a role for CRF(2) in this effect. Urocortin 1 increased LCGU in a dissected hindbrain region. However, central administration of the CRF(2)-selective agonists Urocortin 2 and Stresscopin failed to affect LCGU, which may suggest ligand-dependent receptor activation within the CRF system. The present data supports a role for CRF(2) in the regulation of neuronal glucose metabolism

<it>Nav2 </it>is necessary for cranial nerve development and blood pressure regulation

Abstract Background All-trans retinoic acid (atRA) is required for nervous system development, including the developing hindbrain region. Neuron navigator 2 (Nav2) was first identified as an atRA-responsive gene in human neuroblastoma cells (retinoic acid-induced in neuroblastoma 1, Rainb1), and is required for atRA-mediated neurite outgrowth. In this paper, we explore the importance of Nav2 in nervous system development and function in vivo. Results Nav2 hypomorphic homozygous mutants show decreased survival starting at birth. Nav2 mutant embryos show an overall reduction in nerve fiber density, as well as specific defects in cranial nerves IX (glossopharyngeal) and X (vagus). Nav2 hypomorphic mutant adult mice also display a blunted baroreceptor response compared to wild-type controls. Conclusions Nav2 functions in mammalian nervous system development, and is required for normal cranial nerve development and blood pressure regulation in the adult.</p

Disruption of Murine Mus81 Increases Genomic Instability and DNA Damage Sensitivity but Does Not Promote Tumorigenesis

The Mus81-Eme1 endonuclease is implicated in the efficient rescue of broken replication forks in Saccharomyces cerevisiae and Schizosaccharomyces pombe. We have used gene targeting to study the function of the Mus81-Eme1 endonuclease in mammalian cells. Mus81-deficient mice develop normally and are fertile. Surprisingly, embryonic fibroblasts from Mus81(−/−) animals fail to proliferate in vitro. This proliferation defect can be rescued by expression of the papillomavirus E6 protein that promotes degradation of p53. When grown in culture, Mus81(−/−) cells have elevated levels of DNA damage, acquire chromosomal aberrations, and are hypersensitive to agents that generate DNA cross-links. In contrast to the situation in yeast, murine Mus81 is not required for replication restart following camptothecin treatment. Mus81(−/−) mice and cells are hypersensitive to DNA cross-linking agents. Cross-link-induced double-strand break formation is normal in Mus81(−/−) cells, but the resolution of repair intermediates is not. The persistence of Rad51 foci in Mus81(−/−) cells suggests that Mus81 acts at a late step in the repair of cross-link-induced lesions. Despite these defects, Mus81(−/−) mice do not show increased predisposition to lymphoma or any other malignancy in the first year of life

Modelling Alzheimer's disease in multiple transgenic mice

We have reported transgenic mice with neuronal overexpression of the clinical mutant beta -amyloid precursor protein (APP) known as London, which develop an AD-related phenotype [Moechers, Dewachter, Lorent, Reverse, Baekelandt, Nadiu, Tesseur, Spittaels, Van den Haute, Checler, et al. (1999) J. Biol. Chem. 274, 6483-6492]. Characterized early symptoms (3-9 months) include disturbed behaviour, neophobia, aggression, hypersensitivity to kainic acid, hyposensitivity to N-methyl-D-aspartate, defective cognition and memory, and decreased long-term potentiation. Late in life, at 12-15 months, amyloid plaques develop in the brain and correlate with increased levels of beta -amyloid (A beta )40/42 (the 40- and 42-amino-acid forms of A beta). The formation of amyloid plaques is dissociated in time from and not involved in the early phenotype. Hyperphosphorylated protein tau is present but no tangle pathology is observed. In double-transgenic mice, i.e. APP/London x Presenilin 1, the increased production of A beta 42 results in amyloid plaques developing by the age of 6 months. Transgenic mice with overexpression of either human apolipoprotein E4 (ApoE4) or human protein tau in central neurons develop severe axonopathy in the brain and spinal cord. Progressive degeneration of nerves and muscles is demonstrated by motor problems, wasting and premature death. Tau is hyperphosphorylated but there is no formation of filaments or neurofibrillary tangles. The tangle aspect of AD pathology is still missing from all current transgenic amyloid models. Its implementation will require insight into the cellular signalling pathways which regulate the microtubule-stabilizing function by phosphorylation of neuronal tau

Mammalian Navigators are Microtubule Plus-End Tracking Proteins that can Reorganize the Cytoskeleton to Induce Neurite-Like Extensions

Mammalian microtubule plus-end tracking proteins (+TlPs) specifically associate with the ends of growing microtubules. +TlPs are involved in many cellular processes, including mitosis, cell migration and neurite extension. Navigators are mammalian homologues of the C. elegans unc-53 protein, an ATPase that has been linked to the migration and Outgrowth of muscles, axons and excretory canals. Here we show that all three mammalian Navigators are +TlPs, consistent with a previous on Navigator 1 (NAV1) (Martinez-Lopez et al., Mol Cell Neurosci 2005:28:599-612). Overexpression of GFP-tagged Navigators causes displacement of CAP_GLY-motif containing +TlPs, Such as CLIP-170, from microtubule ends, suggesting that the Navigator-binding, sites on microtubule ends overlap with those of the CAP_GLY-motif proteins. In interphase cells, mammalian Navigators also prominently localize to centrosomes, a localization that does not depend on an intact microtubule network. Fluorescence recovery after photobleaching (FRAP) experiments indicate that NAV1 associates with intracellular structures other than microtubules or centrosomes. Expression of GFP-tagged Navigators induces the formation of neurite-like extensions in non-neuronal cells, showing that Navigators can dominantly alter cytoskeletal behavior. For NAV1 this function depends on its ATPase activity; it is not achieved by a classical type of MT bundling and stabilization. Combined our data suggest that Navigators are +TlPs that call reorganize the cytoskeleton to guide cell shape changes. Our data are consistent with a role for Navigators in neurite outgrowth. Cell Motil