1,720,960 research outputs found
Hypothalamic stem cells: towards a cellular approach to neuroendocrine diseases?
No full textThe mammalian hypothalamus is involved in regulating numerous physiological
functions; however, the molecular pathways that mediate hypothalamic
development are largely unknown. The study of neural stem cells (NSC) offers a
useful model to investigate such mechanisms. Neurospheres of NSC from both
fetal and adult rat hypothalami able to differentiate into glia and neurons with
neuroendocrine markers, have been recently isolated. However, we have setup a
stable cell line of NSC from E12 fetal mouse hypothalamus. The cell line (AC1)
grows as a monolayer in a defined medium enriched in FGF-2 and EGF. AC1
cells express stemness, neuronal, but not astrocytic markers. The study on AC1
cells has been focused on the expression of hypothalamic patterning genes and
the ability to develop neuroendocrine lineages in vitro. AC1 cells may therefore
help to elucidate specific physiological hypothalamic processes and offer a
valuable tool to develop a future cellular approach to neuroendocrine disorders
(i.e., diabetes insipidus, obesity, Prader-Willi syndrome, etc.)
SELADIN-1/DHCR24 GENE OVEREXPRESSION DECREASES MIGRATION OF IMMATURE IMMORTALIZED NEURONS
No full textDHCR24 (3beta-hydroxysterol delta24-reductase) is a key enzyme to form cholesterol from desmosterol; interestingly, high levels of desmosterol are present during fetal brain development. DHCR24 is also called Seladin-1 (for Selective Alzheimer’s Disease Indicator-1, Sel-1) since it is down-regulated in the brain regions more susceptible to this disease. Moreover, it has been implicated in tumor progression, neuroprotection and oxidative stress, suggesting a prosurvival and antiapoptotic action.
In the present study we investigated the expression of Sel-1 in immortalized neurons derived from mature (GT1-7) and immature (GN11) endocrine neurons and a possible role in the neuronal maturation and motility. We found that GT1-7 cells present 100 times higher levels of Sel-1 mRNA and protein compared to GN11 cells as well as a different intracellular distribution. Accordingly, an higher relative amount of desmosterol was present in GN11 cells. In a first series of functional experiments, we found that cyclodextrin-mediated membrane cholesterol/desmosterol substitution did not affect the motility of GN11 cells. By transfection of GN11 cells with a Seladin-1-GFP construct we observed an increase of the cholesterol and a decrease of the desmosterol content, a distribution of the protein similar to mature GT1-7 cells as well as a neurite growth stimulation. Moreover, by microchemotaxis assay, we found that transfected cells showed a decrease of their motility.
In conclusions, these results are suggestive of a possible role of Seladin-1/DHCR24 on some event of neuronal development/differentiation, through a control of the intracellular cholesterol/desmosterol ratio
GnRH and GnRH receptors in the pathophysiology of the human female reproductive system
Full text linkBACKGROUND: Human reproduction depends on an intact hypothalamic-pituitary-gonadal (HPG) axis. Hypothalamic gonadotrophin-releasing hormone (GnRH) has been recognized, since its identification in 1971, as the central regulator of the production and release of the pituitary gonadotrophins that, in turn, regulate the gonadal functions and the production of sex steroids. The characteristic peculiar development, distribution and episodic activity of GnRH-producing neurons have solicited an interdisciplinary interest on the etiopathogenesis of several reproductive diseases. The more recent identification of a GnRH/GnRH receptor (GnRHR) system in both the human endometrium and ovary has widened the spectrum of action of the peptide and of its analogues beyond its hypothalamic function.
METHODS: An analysis of research and review articles published in international journals until June 2015 has been carried out to comprehensively summarize both the well established and the most recent knowledge on the physiopathology of the GnRH system in the central and peripheral control of female reproductive functions and diseases.
RESULTS: This review focuses on the role of GnRH neurons in the control of the reproductive axis. New knowledge is accumulating on the genetic programme that drives GnRH neuron development to ameliorate the diagnosis and treatment of GnRH deficiency and consequent delayed or absent puberty. Moreover, a better understanding of the mechanisms controlling the episodic release of GnRH during the onset of puberty and the ovulatory cycle has enabled the pharmacological use of GnRH itself or its synthetic analogues (agonists and antagonists) to either stimulate or to block the gonadotrophin secretion and modulate the functions of the reproductive axis in several reproductive diseases and in assisted reproduction technology. Several inputs from other neuronal populations, as well as metabolic, somatic and age-related signals, may greatly affect the functions of the GnRH pulse generator during the female lifespan; their modulation may offer new possible strategies for diagnostic and therapeutic interventions. A GnRH/GnRHR system is also expressed in female reproductive tissues (e.g. endometrium and ovary), both in normal and pathological conditions. The expression of this system in the human endometrium and ovary supports its physiological regulatory role in the processes of trophoblast invasion of the maternal endometrium and embryo implantation as well as of follicular development and corpus luteum functions. The GnRH/GnRHR system that is expressed in diseased tissues of the female reproductive tract (both benign and malignant) is at present considered an effective molecular target for the development of novel therapeutic approaches for these pathologies. GnRH agonists are also considered as a promising therapeutic approach to counteract ovarian failure in young female patients undergoing chemotherapy.
CONCLUSIONS: Increasing knowledge about the regulation of GnRH pulsatile release, as well as the therapeutic use of its analogues, offers interesting new perspectives in the diagnosis, treatment and outcome of female reproductive disorders, including tumoral and iatrogenic diseases
VEGF and SEMA3A selectively control different stages of GnRH neuron development independently of blood vessels
No full textGonadotropin-releasing hormone (GnRH) neurons are neuroendocrine cells that are born outside the brain and migrate along olfactory and vomeronasal axons to reach the hypothalamus, where they regulate sexual reproduction. By combining genetic mouse models with cell and molecular approaches, we show here that the development of the GnRH neuronal system relies on the synergistic action of two distinct neuropilin-mediated signalling pathways. Thus, the vascular endothelial growth factor isoform VEGF164 signals through NRP1 to promote the survival of migrating GnRH neurons via PI3K and ERK1/2 activation; unexpectedly, we found that this pathway operates independently of KDR, the VEGF receptor previously implicated in neuronal survival. Concomitantly, SEMA3A signals through NRP1 and, unconventionally, NRP2, to pattern the axonal scaffold that guides the migrating GnRH neurons. The combined loss of VEGF164 and SEMA3A therefore precludes the establishment of the GnRH neuronal system, demonstrating that VEGF164 and SEMA3A cooperate to coordinate neuronal migration with survival
Characterization of a stable cell line of mouse fetal hypothalamic neural stem cells
No full textThe mammalian hypothalamus is involved in regulating several physiological functions; many of these functions are exerted by the neuroendocrine system. The neuroendocrine hypothalamus contains two distinct subsystems, the parvicellular and magnocellular neuronal systems, however, the molecular pathways that mediate the development of such neurons are largely unknown. The study of neural stem cells (NSC) offers a useful model to investigate such mechanisms. Neurospheres of NSC from both fetal and adult rat hypothalami, able to differentiate into glia and neurons, have been recently isolated but the proportion of stem cells in neurosphere is low and they cannot directly observed and studied.
The present communication describes the setup and the characterization of a pure stable cell line of NSC from E12 fetal mouse hypothalamus. The cell line (named AC1) grows as a monolayer in continuous expansion, by symmetrical division, in a defined medium enriched in FGF-2 and EGF. AC1 cells express stemness (nestin, Sox-2 and Pax-6), neuronal, but not astrocytic, markers; moreover, the expression of hypothalamic patterning genes (Sim1, Sim2, Arnt2, Brn2) has been also confirmed. After prolonged expansion, they remain able to differentiate efficiently into neurons and astrocytes in vitro. In normal culture conditions, AC1 were found to express POMC and CRH; however, detectable transcripts for TRH, GHRH and somatostatin were evident after short-term induction of neuronal differentiation. The ability of AC1 cells to develop neuroendocrine lineages in vitro will help to elucidate the mechanisms involved in the specific differentiation of neurohormonal hypothalamic neurons as well as other physiological hypothalamic developmental processes. In perspective, AC1 cells, would offer a new valuable tool to develop future cellular approaches to neuroendocrine disorders (i.e., diabetes insipidus, obesity, Prader-Willi syndrome, etc.)
A novel role for neuritin (cpg15) : the regulation of neuronal migration
No full textNeuritin (Nrn1 or cpg15) is a GPI-anchored protein, originally identified as a candidate plasticity-related gene associated with neurite elongation in several areas of the nervous system. Nrn1 expression is highly up-regulated by neuronal activity, and neurotrophins (BDNF and NT-3). Nrn1 acts in a non-cell autonomous manner to coordinately regulate growth of apposing dendritic and axonal arbors, and to promote synaptic maturation. During PC12 cells differentiation, NGF up-regulates Nrn1 expression, and this enhances the differentiating effects of NGF on PC12 cells favoring the extension of longer neuritis. It has therefore been hypothesized that Nrn1 acts as a downstream effector in promoting neurite outgrowth. Interestingly, Nrn1 expression peaks during neuronal development and particularly in the embryonic proliferative zones. These areas are characterized by an active neuronal migration, a critical event in the development of the nervous system. Neurons and precursor cells migrate using molecular mechanisms which often resembles those involved in neurite outgrowth. Cytoskeletal dynamics, cell adhesion, and chemoattraction/repulsion are all involved both in neuronal migration and neurite extension. A preliminary microarray analysis performed on Gn11 neurons (a model widely utilized to study neuronal migration) showed Nrn1 as one of the more abundant genes expressed in this cell line. Therefore, our goal was to investigate whether Nrn1 regulates neuronal migration. This was performed selecting two similar cell lines, characterized by a different migratory behavior: Gn11 cells (migrating neurons) and GT1-7 cells (non migrating neurons), and analysing their Nrn1 mRNA and protein expression levels. Interestingly, Nrn1 expression is much higher in migrating Gn11 neurons than in non-migrating GT1-7 neurons. In Boyden microchemotaxis and wound-healing assays, the migratory ability of Gn11 neurons is reduced when Nrn1 expression is silenced, while it is increased when Nrn1 is over-expressed. ICC and Western blot analyses of post-translational modifications of tubulin known to be associated with differently dynamic microtubules show an enrichment of stable microtubules in Nrn1 silenced neurons that likely reflects the diminished migratory capability of the cells. These results demonstrate that the migratory properties of Gn11 cells may be altered by modulating Nrn1 levels and strongly suggest, for the first time, that Nrn1 is a regulator of neuronal migration
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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