Nitric oxide regulates neurogenesis in adult olfactory epithelium in vitro

Nitric oxide regulates neurogenesis in the developing and adult brain. The olfactory epithelium is a site of neurogenesis in the adult and previous studies suggest a role for nitric oxide in this tissue during development. We investigated whether neuronal precursor proliferation and differentiation is regulated by nitric oxide using primary cultures of olfactory epithelial cells and an immortalized, clonal, neuronal precursor cell line derived from adult olfactory epithelium. In these cultures NOS inhibition reduced cell proliferation and stimulated neuronal differentiation, including expression of a voltage-dependent potassium conductance of the delayed rectifier type. In the neuronal precursor cell line, differentiation was associated with a significant decrease in nitric oxide release. In contrast, addition of nitric oxide stimulated proliferation and reduced neuronal differentiation. Nitric oxide regulated olfactory neurogenesis independently of added growth factors. Taken together these results indicate that nitric oxide levels can regulate cell proliferation and neuronal differentiation of olfactory precursor cells.     

Isolation and Culture of Adult Zebrafish Brain-derived Neurospheres

The zebrafish is a highly relevant model organism for understanding the cellular and molecular mechanisms involved in neurogenesis and brain regeneration in vertebrates. However, an in-depth analysis of the molecular mechanisms underlying zebrafish adult neurogenesis has been limited due to the lack of a reliable protocol for isolating and culturing neural adult stem/progenitor cells. Here we provide a reproducible method to examine adult neurogenesis using a neurosphere assay derived from zebrafish whole brain or from the telencephalon, tectum and cerebellum regions of the adult zebrafish brain. The protocol involves, first the microdissection of zebrafish adult brain, then single cell dissociation and isolation of self-renewing multipotent neural stem/progenitor cells. The entire procedure takes eight days. Additionally, we describe how to manipulate gene expression in zebrafish neurospheres, which will be particularly useful to test the role of specific signaling pathways during adult neural stem/progenitor cell proliferation and differentiation in zebrafish.     

Gene profiles within the adult subventricular zone niche: proliferation, differentiation and migration of neural progenitor cells in the ischemic brain

Focal cerebral ischemia induces neurogenesis in the subventricular zone (SVZ) of the adult human brain. Neurogenesis is controlled by proliferation, differentiation, and migration of neural progenitor cells. This article reviews emerging data that changes of cell cycle kinetics of neural progenitor cells induced by stroke contribute to increased neural progenitor cell proliferation and that gene profiles control proliferation, differentiation, and migration of neural progenitor cells within the SVZ niche. A better understanding of gene profiles that control the biological function of adult SVZ neural progenitor cells could lead to more selective and effective treatments to enhance neurogenesis during stroke recovery.     

Glial influences on neural stem cell development: cellular niches for adult neurogenesis

Neural stem cells continually generate new neurons in very limited regions of the adult mammalian central nervous system. In the neurogenic regions there are unique and highly specialized microenvironments (niches) that tightly regulate the neuronal development of adult neural stem cells. Emerging evidence suggests that glia, particularly astrocytes, have key roles in controlling multiple steps of adult neurogenesis within the niches, from proliferation and fate specification of neural progenitors to migration and integration of the neuronal progeny into pre-existing neuronal circuits in the adult brain. Identification of specific niche signals that regulate these sequential steps during adult neurogenesis might lead to strategies to induce functional neurogenesis in other brain regions after injury or degenerative neurological diseases.     

Fanconi DNA repair pathway is required for survival and long-term maintenance of neural progenitors

Although brain development abnormalities and brain cancer predisposition have been reported in some Fanconi patients, the possible role of Fanconi DNA repair pathway during neurogenesis is unclear. We thus addressed the role of fanca and fancg, which are involved in the activation of Fanconi pathway, in neural stem and progenitor cells during brain development and adult neurogenesis. Fanca(-/-) and fancg(-/-) mice presented with microcephalies and a decreased neuronal production in developing cortex and adult brain. Apoptosis of embryonic neural progenitors, but not that of postmitotic neurons, was increased in the neocortex of fanca(-/-) and fancg(-/-) mice and was correlated with chromosomal instability. In adult Fanconi mice, we showed a reduced proliferation of neural progenitor cells related to apoptosis and accentuated neural stem cells exhaustion with ageing. In addition, embryonic and adult Fanconi neural stem cells showed a reduced capacity to self-renew in vitro. Our study demonstrates a critical role for Fanconi pathway in neural stem and progenitor cells during developmental and adult neurogenesis.     

Sox11 modulates neocortical development by regulating the proliferation and neuronal differentiation of cortical intermediate precursors

Neural precursor cells play important roles in the neocortical development, but the mechanisms of neural progenitor proliferation, neuronal differentiation, and migration, as well as patterning are still unclear. Sox11, one of SoxC family members, has been reported to be essential for embryonic and adult neurogenesis. But there is no report about the roles of Sox11 in corticogenesis. In order to investigate Sox11 function during cortical development, loss of function experiment was performed in this study. Knockdown of Sox11 by Sox11 siRNA constructs resulted in a diminished neuronal differentiation, but enhanced proliferation of intermediate progenitors. Accompanied with the high expression of Sox11 in the postmitotic neurons, but low expression of Sox11 in the dividing neural progenitors, all the observations indicate that Sox11 induces neuronal differentiation during the neocortical development.     

Regulation of neuronal proliferation and differentiation by nitric oxide

Many studies have revealed the free radical nitric oxide (NO) to be an important modulator of vascular and neuronal physiology. It also plays a developmental role in regulating synapse formation and patterning. Recent studies suggest that NO may also mediate the switch from proliferation to differentiation during neurogenesis. Many mechanisms of this response are conserved between neuronal precursor cells and the cells of the vascular system, where NO can inhibit the proliferative response of endothelial and smooth-muscle cells to injury. In cultured neuroblastoma cells, NO synthase (NOS) expression is increased in the presence of various growth factors and mitogens. Subsequent production of NO leads to cessation of cell division and the acquisition of a differentiated phenotype. The inhibitory action of NO on neuroblast proliferation has also been demonstrated in vivo for vertebrate and invertebrate nervous systems, as well as in the adult brain. Potential downstream effectors of NO include the second messenger cyclic GMP, activation of the tumor-suppressor genes p53 and Rb, and the cyclin-dependent kinase inhibitor p21. These studies highlight a new role for NO in the nervous system, as a coordinator of proliferation and patterning during neural development and adult neurogenesis.     

PI3K/Akt and CREB regulate adult neural hippocampal progenitor proliferation and differentiation

The phosphoinositide 3-OH kinase (PI3K)/Akt pathway has been implicated in regulating several important cellular processes, including apoptosis, survival, proliferation, and metabolism. Using both pharmacological and genetic means, we demonstrate here that PI3K/Akt plays a crucial role in the proliferation of adult hippocampal neural progenitor cells. PI3K/Akt transduces intracellular signals from multiple mitogens, including basic fibroblast growth factor (FGF-2), Sonic hedgehog (Shh), and insulin-like growth factor 1 (IGF-1). In addition, retroviral vector-mediated over-expression of wild type Akt increased cell proliferation, while a dominant negative Akt inhibited proliferation. Furthermore, wild type Akt over-expression reduced glial (GFAP) and neuronal (beta-tubulin III) marker expression during differentiation, indicating that it inhibits cell differentiation. We also show that activation of the cAMP response element binding protein (CREB), which occurs in cells stimulated by FGF-2, is limited when Akt signaling is inhibited, demonstrating a link between Akt and CREB. Over-expression of wild type CREB increases progenitor proliferation, whereas dominant negative CREB only slightly decreases proliferation. These results indicate that PI3K/Akt signaling integrates extracellular signaling information to promote cellular proliferation and inhibit differentiation in adult neural progenitors.     

CREB signalling in neural stem/progenitor cells: recent developments and the implications for brain tumour biology

This paper discusses the evidence for the role of CREB in neural stem/progenitor cell (NSPC) function and oncogenesis and how these functions may be important for the development and growth of brain tumours. The cyclic-AMP response element binding (CREB) protein has many roles in neurons, ranging from neuronal survival to higher order brain functions such as memory and drug addiction behaviours. Recent studies have revealed that CREB also has a role in NSPC survival, differentiation and proliferation. Recent work has shown that over-expression of CREB in transgenic animals can impart oncogenic properties on cells in various tissues and that aberrant CREB expression is associated with tumours in patients. It is the central position of CREB, downstream of key developmental and growth signalling pathways, which give CREB the ability to influence a spectrum of cell activities, such as cell survival, growth and differentiation in both normal and cancer cells.     

DISC1-related signaling pathways in adult neurogenesis of the hippocampus

Disrupted-in-schizophrenia 1 (DISC1) is a multifunctional scaffold protein which plays an important role in neurogenesis and neural development in the adult brain, especially in the dentate gyrus (DG) of the hippocampus. Accumulated research has unveiled the role of DISC1 in several aspects of neural development and neurogenesis, such as neuronal maturation, proliferation, migration, positioning, differentiation, dendritic growth, axonal outgrowth, and synaptic plasticity. Studies on the function of this protein have explored multiple facets, including variants and missense mutants in genetics, proteins interactivity and signaling pathways in molecular biology, and pathogenesis and treatment targets of major mental illness, and more. In this review, we present several signaling pathways discussed in recent research, such as the AKT signaling pathway, GABA signaling pathway, GSK3β signaling pathway, Wnt signaling pathway, and NMDA-R signaling pathway. DISC1 interacts, directly or indirectly, with these signaling pathways and they co-regulate the process of adult neurogenesis in the hippocampus.     

TRIM32-dependent transcription in adult neural progenitor cells regulates neuronal differentiation

In the adult mammalian brain, neural stem cells in the subventricular zone continuously generate new neurons for the olfactory bulb. Cell fate commitment in these adult neural stem cells is regulated by cell fate-determining proteins. Here, we show that the cell fate-determinant TRIM32 is upregulated during differentiation of adult neural stem cells into olfactory bulb neurons. We further demonstrate that TRIM32 is necessary for the correct induction of neuronal differentiation in these cells. In the absence of TRIM32, neuroblasts differentiate slower and show gene expression profiles that are characteristic of immature cells. Interestingly, TRIM32 deficiency induces more neural progenitor cell proliferation and less cell death. Both effects accumulate in an overproduction of adult-generated olfactory bulb neurons of TRIM32 knockout mice. These results highlight the function of the cell fate-determinant TRIM32 for a balanced activity of the adult neurogenesis process.