Injury-induced neurogenesis in the mammalian forebrain

It has been accepted that new neurons are added to the olfactory bulb and the hippocampal dentate gyrus throughout life in the healthy adult mammalian brain. Recent studies have clarified that brain insult raises the proliferation of neural stem cells/neural progenitor cells existing in the subventricular zone and the subgranular zone, which become sources of new neurons for the olfactory bulb and the dentate gyrus, respectively. Interestingly, convincing data has shown that brain insult invokes neurogenesis in various brain regions, such as the hippocampal cornu ammonis region, striatum, and cortex. These reports suggest that neural stem cells/neural progenitor cells, which can be activated by brain injury, might be broadly located in the adult brain or that new neurons may migrate widely from the neurogenic regions. This review focuses on brain insult-induced neurogenesis in the mammalian forebrain, especially in the neocortex.     

Moving towards a paradigm: common mechanisms of chemotactic signaling in Dictyostelium and mammalian leukocytes

Chemotaxis, or directed migration of cells along a chemical gradient, is a highly coordinated process that involves gradient sensing, motility, and polarity. Most of our understanding of chemotaxis comes from studies of cells undergoing amoeboid-type migration, in particular the social amoeba Dictyostelium discoideum and leukocytes. In these amoeboid cells the molecular events leading to directed migration can be conceptually divided into four interacting networks: receptor/G protein, signal transduction, cytoskeleton, and polarity. The signal transduction network occupies a central position in this scheme as it receives direct input from the receptor/G protein network, as well as feedback from the cytoskeletal and polarity networks. Multiple overlapping modules within the signal transduction network transmit the signals to the actin cytoskeleton network leading to biased pseudopod protrusion in the direction of the gradient. The overall architecture of the networks, as well as the individual signaling modules, is remarkably conserved between Dictyostelium and mammalian leukocytes, and the similarities and differences between the two systems are the subject of this review.     

Mechanism of neurogenesis in adult avian brain

Adult neurogenesis in birds offers unique opportunities to study basic questions addressing the birth, migration and differentiation of neurons. Neurons in adult canaries originate from discrete proliferative regions on the walls of the lateral ventricles. They migrate away from their site of birth, initially at high rates, along the processes of radical cells. The rates of dispersal diminish as the young neurons invade regions devoid of radial fibers, probably under the guidance of other cues. The discrete sites of birth in the ventricular zone generate neurons that end up differentiating throughout the telencephalon. New neurons may become interneurons or projection neurons; the latter connect two song control nuclei between neostriatum and archistriatum. Radial cells, that in mammals disappear as neurogenesis comes to an end, persist in the adult avian brain. The presence of radial cells may be key to adult neurogenesis. Not only do they serve as guides for initial dispersal, they also divide and may be the progenitors of new neurons.     

Mechanism of neurogenesis in adult avian brain

Summary Adult neurogenesis in birds offers unique opportunities to study basic questions addressing the birth, migration and differentiation of neurons. Neurons in adult canaries originate from discrete proliferative regions on the walls of the lateral ventricles. They migrate away from their site of birth, initially at high rates, along the processes of radial cells. The rates of dispersal diminish as the young neurons invade regions devoid of radial fibers, probably under the guidance of other cues. The discrete sites of birth in the ventricular zone generate neurons that end up differentiating throughout the telencephelon. New neurons may become interneurons or projection neurons; the latter connect two song control nuclei between neostriatum and archistriatum. Radial cells, that in mammals disappear as neurogenesis comes to an end, persist in the adult avian brain. The presence of radial cells may be key to adult neurogenesis. Not only do they serve as guides for initial dispersal, they also divide and may be the progenitors of new neurons.     

Insulin/IGF signalling in neurogenesis

No Abstract. . Received 25 January 2006; received after revision 29 March 2006; accepted 2 May 2006     

Tumor suppressive pathways in the control of neurogenesis

The generation of specialized neural cells in the developing and postnatal central nervous system is a highly regulated process, whereby neural stem cells divide to generate committed neuronal progenitors, which then withdraw from the cell cycle and start to differentiate. Cell cycle checkpoints play a major role in regulating the balance between neural stem cell expansion and differentiation. Loss of tumor suppressors involved in checkpoint control can lead to dramatic alterations of neurogenesis, thus contributing to neoplastic transformation. Here we summarize and critically discuss the existing literature on the role of tumor suppressive pathways and their regulatory networks in the control of neurogenesis and transformation.     

Ultrastructural visualization of Cabot rings in pernicious anemia

Summary Using the ammoniacal silver stain, Cabot rings were identified in peripheral blood erythrocytes from patients with severe untreated pernicious anemia. Ultrastructural studies of these erythrocytes showed silver deposits in partial loops and figure-eight forms, indicating that arginine rich histone may be a prominent component of the Cabot ring.Supported in part by the Elizabeth Roodvoets Memorial Grant for Cancer Research of the American Cancer Society (No. CI-79) and by National Cancer Institute Grant USPHS No. CA 14428-02.     

Interkinetic nuclear migration: beyond a hallmark of neurogenesis

Interkinetic nuclear migration (INM) is an oscillatory nuclear movement that is synchronized with the progression of the cell cycle. The efforts of several researchers, following the first report of INM in 1935, have revealed many of the molecular mechanisms of this fascinating phenomenon linking the timing of the cell cycle and nuclear positioning in tissue. Researchers are now faced with a more fundamental question: is INM important for tissue, particularly brain, development? In this review, I summarize the current understanding of the regulatory mechanisms governing INM, investigations involving several different tissues and species, and possible explanations for how nuclear movement affects cell-fate determination and tissue formation.     

Sphingolipids in mammalian cell signalling

Sphingolipids and their metabolites, ceramide, sphingosine and sphingosine-1-phosphate, are involved in a variety of cellular processes including differentiation, cellular senescence, apoptosis and proliferation. Ceramide is the main second messenger, and is produced by sphingomyelinase-induced hydrolysis of sphingomyelin and by de novo synthesis. Many stimuli, e.g. growth factors, cytokines, G protein-coupled receptor agonists and stress (UV irradiation) increase cellular ceramide levels. Sphingomyelin in the plasma membrane is located primarily in the outer (extracellular) leaflet of the bilayer, whilst sphingomyelinases are found at the inner (cytosolic) face and within lysosomes/endosomes. Such cellular compartmentalisation restricts the site of ceramide production and subsequent interaction with target proteins. Glycosphingolipids and sphingomyelin together with cholesterol are major components of specialised membrane microdomains known as lipid rafts, which are involved in receptor aggregation and immune responses. Many signalling molecules, for example Src family tyrosine kinases and glycosylinositolphosphate-anchored proteins, are associated with rafts, and disruption of these domains affects cellular responses such as apoptosis. Sphingosine and sphingosine-1-phosphate derived from ceramide are also signalling molecules. In particular, sphingosine-1-phosphate is involved in proliferation, differentiation and apoptosis. Sphingosine-1-phosphate can act both extracellularly through endothelial-differentiating gene (EDG) family G protein-coupled receptors and intracellularly through direct interactions with target proteins. The importance of sphingolipid signalling in cardiovascular development has been reinforced by recent reports implicating EDG receptors in the regulation of embryonic cardiac and vascular morphogenesis. Received 16 May 2001; received after revision 29 June 2001; accepted 3 July 2001     

Ultrastructural visualization of Cabot rings in pernicious anemia.

Using the ammoniacal silver stain, Cabot rings were identified in peripheral blood erythrocytes from patients with severe untreated pernicious anemia. Ultrastructural studies of these erythrocytes showed silver deposits in partial loops and figure-eight forms, indicating that arginine rich histone may be a prominent component of the Cabot ring.     

Fluorophores as visualization aides in agar growth media

Summary A survey of 26 fluorophores revealed 5 which were non-inhibitory toStaphylococcus aureus andEscherichia coli and produced low background and high colony fluorescence.     

Regulation of cyclin-Cdk activity in mammalian cells

Cell cycle progression is driven by the coordinated regulation of the activities of cyclin-dependent kinases (Cdks). Of the several mechanisms known to regulate Cdk activity in response to external signals, regulation of cyclin gene expression, post-translational modification of Cdks by phosphorylation-dephosphorylation cascades, and the interaction of cyclin/Cdk complexes with protein inhibitors have been thoroughly studied. During recent years, much attention has also been given to mechanisms that regulate protein degradation by the ubiquitin/proteasome pathway, as well as to the regulation of subcellular localization of the proteins that comprise the intrinsic cell cycle clock. The purpose of the present review is to summarize the most important aspects of the various mechanisms implicated in cell cycle regulation.     

Improved visualization of wall ultrastructure inSaccharomyces cerevisiae

Riassunto Usando fissativi contenenti TAPO é stata migliorata la visualizzazione dei componenti strutturali della parete cellulare diSaccharomyces cerevisiae; questa é stata paragonato con quella osservata precedentemente inCandida albicans.

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Acknowledgment. The author thanks Mr.B. Pasquetti and Mr.M. Mari for their excellent technical assistence.     

Y-family DNA polymerases in mammalian cells

Eukaryotic genomes are replicated with high fidelity to assure the faithful transmission of genetic information from one generation to the next. The accuracy of replication relies heavily on the ability of replicative DNA polymerases to efficiently select correct nucleotides for the polymerization reaction and, using their intrinsic exonuclease activities, to excise mistakenly incorporated nucleotides. Cells also possess a variety of specialized DNA polymerases that, by a process called translesion DNA synthesis (TLS), help overcome replication blocks when unrepaired DNA lesions stall the replication machinery. This review considers the properties of the Y-family (a subset of specialized DNA polymerases) and their roles in modulating spontaneous and genotoxic-induced mutations in mammals. We also review recent insights into the molecular mechanisms that regulate PCNA monoubiquitination and DNA polymerase switching during TLS and discuss the potential of using Y-family DNA polymerases as novel targets for cancer prevention and therapy.