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H M Cooper

Publications and source records attributed to H M Cooper.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of neogenin-expressing neural progenitor populations and migrating neuroblasts in the embryonic mouse forebrain.

Many studies have demonstrated a role for netrin-1-deleted in colorectal cancer (DCC) interactions in both axon guidance and neuronal migration. Neogenin, a member of the DCC receptor family, has recently been shown to be a chemorepulsive axon guidance receptor for the repulsive guidance molecule (RGM) family of guidance cues [Rajagopalan S, Deitinghoff L, Davis D, Conrad S, Skutella T, Chedotal A, Mueller B, Strittmatter S (2004) Neogenin mediates the action of repulsive guidance molecule. Nat Cell Biol 6:755-762]. Here we show that neogenin is present on neural progenitors, including neurogenic radial glia, in the embryonic mouse forebrain suggesting that neogenin expression is a hallmark of neural progenitor populations. Neogenin-positive progenitors were isolated from embryonic day 14.5 forebrain using flow cytometry and cultured as neurospheres. Neogenin-positive progenitors gave rise to neurospheres displaying a high proliferative and neurogenic potential. In contrast, neogenin-negative forebrain cells did not produce long-term neurosphere cultures and did not possess a significant neurogenic potential. These observations argue strongly for a role for neogenin in neural progenitor biology. In addition, we also observed neogenin on parvalbumin- and calbindin-positive interneuron neuroblasts that were migrating through the medial and lateral ganglionic eminences, suggesting a role for neogenin in tangential migration. Therefore, neogenin may be a multi-functional receptor regulating both progenitor activity and neuroblast migration in the embryonic forebrain.

Animals↗
PubMed2006

Light-induced Fos expression in the suprachiasmatic nucleus of the four-striped field mouse, Rhabdomys pumilio: A southern African diurnal rodent.

Previous studies have suggested that nocturnal and diurnal species of rodents differ in their circadian responses to light including phase shifts and early gene expression. Rhabdomys pumilio, the four-striped field mouse, is diurnal both in nature and in the laboratory. We studied in this species the response of the suprachiasmatic nucleus (SCN) to light stimuli at different time periods using light-induced expression of Fos as marker of neuronal activity. Fos induction in the SCN was investigated using immunohistochemistry and quantitative image analysis. The animals were exposed to a 15 min light pulse with monochromatic green light at different circadian times throughout a 24-h cycle. Animals maintained in constant darkness served as controls. R. pumilio exhibited an endogenous Fos rhythm in the SCN during constant darkness with highest expression during the subjective day at circadian time (CT) 2 and CT10. Photic stimulation resulted in significant Fos induction in the SCN at CT6, CT14, CT18 and CT22, compared to controls kept in constant darkness, with a peak of expression at CT22, i.e. during late subjective night, mainly due to expression in the ventral SCN. In tract tracing experiments based on the use of cholera toxin subunit B, we found that retinal fibres innervate mainly the contralateral ventral SCN. The intergeniculate leaflet received bilateral retinal innervation with overlap between ipsilateral and contralateral fibres. Altogether the data show that the rodent R. pumilio is a unique diurnal model for chronobiological studies.

Animals↗
PubMed2005

Localization of immunoreactivity for deleted in colorectal cancer (DCC), the receptor for the guidance factor netrin-1, in ventral tier dopamine projection pathways in adult rodents.

DCC (deleted in colorectal cancer)-the receptor of the netrin-1 neuronal guidance factor-is expressed and is active in the central nervous system (CNS) during development, but is down-regulated during maturation. The substantia nigra contains the highest level of netrin-1 mRNA in the adult rodent brain, and corresponding mRNA for DCC has also been detected in this region but has not been localized to any particular neuron type. In this study, an antibody raised against DCC was used to determine if the protein was expressed by adult dopamine neurons, and identify their distribution and projections. Significant DCC-immunoreactivity was detected in midbrain, where it was localized to ventrally displaced A9 dopamine neurons in the substantia nigra, and ventromedial A10 dopamine neurons predominantly situated in and around the interfascicular nucleus. Strong immunoreactivity was not detected in dopamine neurons found elsewhere, or in non-dopamine-containing neurons in the midbrain. Terminal fields selectively labeled with DCC antibody corresponded to known nigrostriatal projections to the dorsolateral striatal patches and dorsomedial shell of the accumbens, and were also detected in prefrontal cortex, septum, lateral habenular and ventral pallidum. The unique distribution of DCC-immunoreactivity in adult ventral midbrain dopamine neurons suggests that netrin-1/DCC signaling could function in plasticity and remodeling previously identified in dopamine projection pathways. In particular, a recent report that DCC is regulated through the ubiquitin-proteosome system via Siah/Sina proteins, is consistent with a potential involvement in genetic and sporadic forms of Parkinson's disease.

Animals↗
PubMed2005

Fos expression in the suprachiasmatic nucleus in response to light stimulation in a solitary and social species of African mole-rat (family Bathyergidae).

Mole-rats are strictly subterranean rodents that are rarely exposed to environmental light. They are well adapted to their environment and have reduced eyes and a severely regressed visual system. It has been shown, however, that mole-rats do exhibit endogenous circadian rhythms that can be entrained, suggesting an intact and functional circadian system. To determine whether light is the entraining agent in these animals, Fos expression in response to light pulses at different circadian times was investigated to obtain phase response curves. Light is integrated effectively in the suprachiasmatic nucleus of the Cape mole-rat (Georychus capensis), and Fos expression is gated according to the phase of the circadian clock. The Fos response in the Cape mole-rat was comparable to that of aboveground rodents. In contrast, the highveld mole-rat (Cryptomys hottentotus pretoriae) was less sensitive to light and did not show a selective Fos response according to the phase of the circadian cycle. Social species appear to be less sensitive to light than their solitary counterparts, which compares well with results from locomotor activity studies.

Analysis of Variance↗
PubMed2002

Characterization of calbindin-positive cones in primates.

The aim of this study is to characterize calbindin-positive photoreceptors and their opsin content in the retina of nocturnal prosimians (Microcebus murinus), New World monkeys (Callithrix jacchus), Old World monkeys (Macaca fascicularis), and humans. To identify the calbindin and opsin content of cones, combined multiple labeling with different fluorescent probes, antibodies directed against calbindin, short, and mid-long wavelength opsins, and lectin peanut agglutinin cytochemistry were used. With the exception of Microcebus, calbindin is present in the cones of all primates but is absent from rods. The distribution of calbindin is similar in human and macaque cones, with dense label in the inner segment, cell body, axon and cone pedicle. Cones in marmoset also show dense staining in the cell body, axon and pedicle but only light label in the inner segment. Primate cone outer segments do not contain calbindin. In the primates studied, three patterns of calbindin and opsin localization are observed. In macaque and marmoset all short and mid-long wavelength cones contain calbindin. In humans, all mid-long wavelength cones contain calbindin whereas all short wavelength cones are devoid of calbindin as confirmed by confocal microscopy. In the nocturnal prosimian Microcebus none of the mid-long or short wavelength cones contain calbindin. In addition to primates, calbindin is absent in cones of other nocturnal species but is present in cones of diurnal species suggesting a difference in the role of calbindin possibly related to the adaptational states or other photoreceptor properties.

Adult↗
PubMed2002

Analysis of immunohistochemical label of Fos protein in the suprachiasmatic nucleus: comparison of different methods of quantification.

The induction of the proto-oncogene c-fos, and its phosphoprotein product Fos, has been extensively used to study the effects of light on the circadian pacemaker in the suprachiasmatic nucleus (SCN). Experimental approaches to the quantification of Fos induction have mainly been based on immunohistochemistry and subsequent measure of Fos immunoreactivity (IR) in sections of the SCN. In this study, the authors compare several methods of quantification using optical density image analysis or counts of Fos-IR labeled cells. To assess whether optical density measures using image analysis reflect the amount of Fos in brain tissue, the authors developed standards of known concentrations of Fos protein in an agar matrix. The agar standards were sectioned and treated simultaneously with sections of the SCN from animals exposed to different levels of irradiance. Optical density was found to be proportional to the quantity of Fos in the sections, indicating that this measure accurately reflects relative levels of Fos protein induction. Quantification by optical density analysis allows an objective measure in which the various parameters, conditions of illumination, and threshold can be maintained constant throughout the analysis. Counting cells by visual observation is more subjective because threshold values cannot be precisely defined and can vary according to the observer, illumination, degree of label, and other factors. In addition, cell counts involving direct visual observation, automated cell counts, or stereological methods do not take into account the difference in the density of label between cells, thus giving equal weight to lightly or densely stained cells. These measures are more or less weakly correlated with measures of optical density and thus do not accurately reflect the amount of bound Fos protein in the tissue sections. In contrast, labeled surface area as measured by image analysis shows a linear relationship with optical density. The main outcome of this study is that computer-assisted image analysis provides an accurate and rapid method to determine the relative amount of Fos protein in the SCN and the effects of light on intracellular signaling mechanisms involved in the circadian clock.

3,3'-Diaminobenzidine↗
PubMed2001

Short and mid-wavelength cone distribution in a nocturnal Strepsirrhine primate (Microcebus murinus).

Strepsirrhines are of considerable interest for understanding the evolution of cone photoreceptors because they represent the most ancestral living primates. The retina of nocturnal Strepsirrhines is reported to contain a single population of medium/long wavelength (MW/LW) cones whereas short wavelength (SW) cones are totally absent. The area centralis of nocturnal Strepsirrhines also lacks the degree of central specialization seen in the fovea of diurnal primates. In this study of a nocturnal Strepsirrhine, the gray mouse lemur (Microcebus murinus), we used specific antibodies that recognize SW and MW/LW opsins to determine the presence of different cone subtypes and their distribution in relation to that of rods and ganglion cells. The results are compared to two diurnal Haplorhine species, a New World (Callithrix jacchus) and an Old World (Macaca fascicularis) monkey. In the mouse lemur, both antibodies to MW/LW cone opsin (COS-1 and CERN956) label the same population of cones. A small proportion of SW cones is only stained by the JH455 antiserum whereas the monoclonal OS-2 antibody shows negative staining. These two antibodies label the same SW cone population in other primates. The extracellular matrix of all cones is also labeled by the peanut agglutinin (PNA) lectin. In mouse lemur retinal wholemounts, peak cone density is localized at the area centralis and ranged from 7,500 to 8,000 cones/mm(2). SW cones represent less than 0.2 % of the total cone population and are mainly located in the nasal part of the retina. SW cones show an irregular distribution and densities never exceed 49 cones/mm(2). The distribution of neurons in the ganglion cell layer shows a distinct centroperipheral gradient with a peak of 28,000 cells/mm(2) at the area centralis. Rod distribution shows a centroperipheral gradient with the peak (850,000 rods/mm(2)) including and extending slightly dorsal to the area centralis. The theoretical spatial resolution of the mouse lemur (4.9 cycles/degree) is slightly lower to that of other nocturnal primates. The densities of rods, cones, and ganglion cell layer neurons represent a compromise between spatial resolution and sensitivity for both photopic and scotopic vision.

Animals↗
PubMed2001

Artificially accelerated aging by shortened photoperiod alters early gene expression (Fos) in the suprachiasmatic nucleus and sulfatoxymelatonin excretion in a small primate, Microcebus murinus.

In mammals, a number of anatomical and functional changes occur in the circadian timing system with aging. In certain species, aging can be modified by various factors which induce a number of pathological changes. In a small primate, the gray mouse lemur (Microcebus murinus), long-term acceleration of seasonal rhythms by exposing the animals to a shortened photoperiodic regime (up to 2.5 times the natural photoperiodic regime) alters longevity, based on survival curves and morphological changes. This provides a model for challenging the idea that modifications of the circadian pacemaker are related to chronological (years) versus biological (photoperiodic cycles) age. To assess the effect of aging and accelerated aging on the circadian pacemaker of this primate, we measured body weight variations, the daily rhythm in urine 6-sulfatoxymelatonin and the light-induced expression of the immediate early gene (Fos) in the suprachiasmatic nucleus of mouse lemurs that had been exposed to different photoperiodic cycles. Urine samples were collected throughout the day and urine 6-sulfatoxymelatonin levels were measured by radioimmunoassay. Light-induced Fos expression in the suprachiasmatic nucleus was studied by exposing the animals to a 15-min monochromatic pulse of light (500 nm) at saturating or sub-saturating levels of irradiance (10(11) or 10(14) photons/cm(2)/s) during the dark phase. The classical pattern of 6-sulfatoxymelatonin excretion was significantly altered in aged mouse lemurs which failed to show a nocturnal peak. Fos expression following exposure to low levels of irradiance was reduced by 88% in the suprachiasmatic nucleus of aged mouse lemurs. Exposure to higher irradiance levels showed similar results, with a reduction of 66% in Fos expression in the aged animals. Animals subjected to artificially accelerated aging demonstrated the same alterations in melatonin production and Fos response to light as animals that had been maintained in a routine photoperiodic cycle. Our data indicate that there are dramatic changes in melatonin production and in the cellular response to photic input in the suprachiasmatic nucleus of aged mouse lemurs, and that these alterations depend on the number of expressed seasonal cycles rather than on a fixed chronological age. These results provide new insights into the mechanisms underlying artificial accelerated aging at the level of the molecular mechanisms of the biological clock.

Aging↗
PubMed2001

Netrin-3 protein is localized to the axons of motor, sensory, and sympathetic neurons.

The netrin family of axon guidance cues has been shown to play a pivotal role in the guidance of a variety of axon projections during embryonic development, both in the vertebrate and invertebrate. While the guidance potential of netrin-1 has been examined in depth in many regions of the developing mouse brain very little information is available on the expression and activity of netrin-3. Here we show that the netrin-3 protein is present on motor neurons and subpopulations of neurons within sensory and sympathetic ganglia. Moreover, significant levels of netrin-3 protein were found to be associated with the axons projecting from these neurons suggesting a role for netrin-3 in axon pathfinding and fasciculation within the peripheral nervous system.

Animals↗
PubMed2001

Localization of the netrin guidance receptor, DCC, in the developing peripheral and enteric nervous systems.

Over recent years the secreted guidance cue, netrin-1, and its receptor, DCC, have been shown to be an essential guidance system driving axon pathfinding within the developing vertebrate central nervous system (CNS). Mice lacking DCC exhibit severe defects in commissural axon extension towards the floor plate demonstrating that the DCC-netrin guidance system is largely responsible for directing axonal projections toward the ventral midline in the developing spinal cord (Fazeli et al., Nature 386 (1997) 796). In addition, these mutants lack several major commissures within the forebrain, including the corpus callosum and the hippocampal commissure. In contrast to the CNS, the role of the DCC guidance receptor in the development of the mammalian peripheral and enteric nervous systems (PNS and ENS) has not been investigated. Here we demonstrate using immunohistochemical analysis that the DCC receptor is present in the developing mouse PNS where it is found on spinal, segmental, and sciatic nerves, and in developing sensory ganglia and their associated axonal projections. In addition, DCC is present in the ENS throughout the early developmental phase.

Animals↗
PubMed2000

A fully functional rod visual pigment in a blind mammal. A case for adaptive functional reorganization?

In the blind subterranean mole rat Spalax ehrenbergi superspecies complete ablation of the visual image-forming capability has been accompanied by an expansion of the bilateral projection from the retina to the suprachiasmatic nucleus. We have cloned the open reading frame of a visual pigment from Spalax that shows >90% homology with mammalian rod pigments. Baculovirus expression yields a membrane protein with all functional characteristics of a rod visual pigment (lambda(max) = 497 +/- 2 nm; pK(a) of meta I/meta II equilibrium = 6.5; rapid activation of transducin in the light). We not only provide evidence that this Spalax rod pigment is fully functional in vitro but also show that all requirements for a functional pigment are present in vivo. The physiological consequences of this unexpected finding are discussed. One attractive option is that during adaptation to a subterranean lifestyle, the visual system of this mammal has undergone mosaic reorganization, and the visual pigments have adapted to a function in circadian photoreception.

Amino Acid Sequence↗
PubMed2000

p(1),p(4)-diadenosine 5'-tetraphosphate induces the uptake of arginine and citrulline by a pore on the plasma membrane of bovine aortic endothelial cells.

We have previously demonstrated that p(1),p(4)-diadenosine 5'-tetraphosphate (Ap(4)A) induces the release of nitric oxide (NO) and modulates the uptake of extracellular L-arginine (L-Arg) and L-citrulline (L-Cit) by bovine aortic endothelial cells (BAEC) [Hilderman, R.H. and Christensen, E.F. (1998) FEBS Lett. 427, 320-324 and Hilderman, R.H., Casey, T.E. and Pojoga, L.H. (2000) Arch. Biochem. Biophys. 375, 124-130]. In this communication we report that extracellular Ap(4)A enhances the uptake of L-Arg and L-Cit through a pore on the plasma membrane of BAEC that is selective for these two amino acids. We also demonstrate that Ap(2)A, which induces NO release, enhances L-Arg uptake while Ap(5)A, a vasoconstrictor, does not enhance the uptake of L-Arg. The potential physiological significance of the uptake of these two amino acids in relation to NO synthesis is discussed.

Animals↗
PubMed2000

Effects of irradiance and stimulus duration on early gene expression (Fos) in the suprachiasmatic nucleus: temporal summation and reciprocity.

The daily behavioral, physiological, and hormonal rhythms in mammals are regulated by an endogenous circadian clock located in the suprachiasmatic nucleus (SCN) and are synchronized by the natural 24 hr light/dark cycle. We studied the response properties (threshold, saturation, and linearity) of the photic system to irradiance by assaying light induction of Fos, the protein product of the immediate early gene c-fos. Fos expression was quantified by image analysis in the SCN and in the retina. Fos expression in the SCN and retina are unrelated because the response differs in terms of threshold, saturation, and range. In the SCN, Fos expression increases proportionately to increases in both irradiance and duration of light exposure. The photic system shows a linear temporal integration of photons for durations ranging from 3 sec to 47.5 min. The principal result of this study shows that in the SCN, Fos expression is directly proportional to the total number of photons rather than to irradiance or duration alone (reciprocity), and that integration occurs over a range of 5 log units of photon number. This report provides the first demonstration that the mechanism of photon integration by the circadian system is expressed at a cellular level in the SCN.

Animals↗
PubMed2000

In vivo functional analysis of the human mitochondrial DNA polymerase POLG expressed in cultured human cells.

The human gene POLG encodes the catalytic subunit of mitochondrial DNA polymerase, but its precise roles in mtDNA metabolism in vivo have not hitherto been documented. By expressing POLG fusion proteins in cultured human cells, we show that the enzyme is targeted to mitochondria, where the Myc epitope-tagged POLG is catalytically active as a DNA polymerase. Long-term culture of cells expressing wild-type POLG-myc revealed no alterations in mitochondrial function. Expression of POLG-myc mutants created dominant phenotypes demonstrating important roles for the protein in mtDNA maintenance and integrity. The D198A amino acid replacement abolished detectable 3'-5' (proofreading) exonuclease activity and led to the accumulation of a significant load (1:1700) of mtDNA point mutations during 3 months of continuous culture. Further culture resulted in the selection of cells with an inactivated mutator polymerase, and a reduced mutation load in mtDNA. Transient expression of POLG-myc variants D890N or D1135A inhibited endogenous mitochondrial DNA polymerase activity and caused mtDNA depletion. Deletion of the POLG CAG repeat did not affect enzymatic properties, but modestly up-regulated expression. These findings demonstrate that POLG exonuclease and polymerase functions are essential for faithful mtDNA maintenance in vivo, and indicate the importance of key residues for these activities.

Amino Acid Substitution↗
PubMed2000

DCC plays a role in navigation of forebrain axons across the ventral midbrain commissure in embryonic xenopus.

In the developing vertebrate brain, growing axons establish a scaffold of axon tracts connected across the midline via commissures. We have previously identified a population of telencephalic neurons that express NOC-2, a novel glycoform of the neural cell adhesion molecule N-CAM that is involved in axon guidance in the forebrain. These axons arise from the presumptive telencephalic nucleus, course caudally along the principal longitudinal tract of the forebrain, cross the ventral midline in the midbrain, and then project to the contralateral side of the brain. In the present study we have investigated mechanisms controlling the growth of these axons across the ventral midline of the midbrain. The axon guidance receptor DCC is expressed by the NOC-2 population of axons both within the longitudinal tract and within the ventral midbrain commissure. Disruption of DCC-dependent interactions, both in vitro and in vivo, inhibited the NOC-2 axons from crossing the ventral midbrain. Instead, these axons grew along aberrant trajectories away from the midline, suggesting that DCC-dependent interactions are important for overcoming inhibitory mechanisms within the midbrain of the embryonic vertebrate brain. Thus, coordinated responsiveness of forebrain axons to both chemostimulatory and chemorepulsive cues appears to determine whether they cross the ventral midline in the midbrain.

Animals↗
PubMed2000

Expression of the netrin-1 receptor, deleted in colorectal cancer (DCC), is largely confined to projecting neurons in the developing forebrain.

Axon guidance mechanisms are crucial to the development of an integrated nervous system. One family of molecules that may be important in establishing axonal connectivity in mammals is the Netrins, and their putative receptors DCC (deleted in colorectal cancer), Neogenin, and Unc-5. Knockout and mutational analyses of some of these genes have shown that they are critically involved in the development of several specific pathways in the developing brain. However, previous expression analyses of these genes have largely been confined to the developing spinal cord. In the present study, we analyzed the expression of DCC in the developing mouse forebrain. We found that DCC protein is expressed in specific axonal populations projecting from the developing olfactory bulb, neocortex, hippocampus, and epithalamus/habenular complex. In the developing olfactory bulb and neocortex, DCC expression is particularly evident during the targeting phase of axon outgrowth and is then rapidly downregulated. As predicted from the knockout and mutational analyses of this gene, DCC is expressed in axonal commissures, in particular the corpus callosum, hippocampal commissure, and the anterior commissure. In addition, we found that DCC is expressed in the habenular commissure, the fasciculus retroflexus, and the stria medularis. Therefore, this analysis implicates a function for DCC in additional axonal guidance systems not predicted from the knockout and mutational analyses.

Animals↗
PubMed2000

The spatial and temporal expression patterns of netrin receptors, DCC and neogenin, in the developing mouse retina.

Recently it has been demonstrated that the guidance of retinal ganglion cell (rgc) axons through the optic disc is dependent on the DCC/netrin-1 axonal guidance system. To gain further insight into the function of the netrin receptors, DCC and Neogenin, in retinal development we have studied the expression patterns of these receptors in the embryonic mouse retina. Neogenin mRNA was restricted to a single neural cell type, the rgc. However, strong Neogenin mRNA expression was observed in the extending fiber cells of the developing lens suggesting a role for Neogenin in the migration events shaping the early lens. Our studies demonstrated that DCC mRNA was expressed at high levels in chains of closely opposed neurons as they migrated towards the emerging mantle layer in the early retina (E12.5-E13.5) suggesting a role for DCC in the migration of neurons out of the ventricular zone. DCC protein expression was high on rgc axons as they actively navigated through the optic disc into the optic nerve. At birth, when the majority of rgc axons had projected through the optic disc, DCC protein was no longer detectable on the distal axonal segments within the optic nerve despite significant DCC protein expression on the proximal axonal membranes in the nerve fiber layer. These observations suggest that a localized down-regulation of DCC protein occurs on projecting axonal membranes once the DCC guidance function is no longer required. We also demonstrated that DCC mRNA and protein were expressed by amacrine cells and Müller glial cells while DCC mRNA was detected in horizontal cells. Taken together, these expression patterns suggest a role for DCC in axon outgrowth and/or pathfinding for a variety of retinal neurons and in the migration of newly born neurons within the developing retina.

Animals↗