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  • Hes5 expression in the postnatal and adult mouse inner ear and the drug-damaged cochlea. 19373512

    The Notch signaling pathway is known to have multiple roles during development of the inner ear. Notch signaling activates transcription of Hes5, a homologue of Drosophila hairy and enhancer of split, which encodes a basic helix-loop-helix transcriptional repressor. Previous studies have shown that Hes5 is expressed in the cochlea during embryonic development, and loss of Hes5 leads to overproduction of auditory and vestibular hair cells. However, due to technical limitations and inconsistency between previous reports, the precise spatial and temporal pattern of Hes5 expression in the postnatal and adult inner ear has remained unclear. In this study, we use Hes5-GFP transgenic mice and in situ hybridization to report the expression pattern of Hes5 in the inner ear. We find that Hes5 is expressed in the developing auditory epithelium of the cochlea beginning at embryonic day 14.5 (E14.5), becomes restricted to a particular subset of cochlear supporting cells, is downregulated in the postnatal cochlea, and is not present in adults. In the vestibular system, we detect Hes5 in developing supporting cells as early as E12.5 and find that Hes5 expression is maintained in some adult vestibular supporting cells. In order to determine the effect of hair cell damage on Notch signaling in the cochlea, we damaged cochlear hair cells of adult Hes5-GFP mice in vivo using injection of kanamycin and furosemide. Although outer hair cells were killed in treated animals and supporting cells were still present after damage, supporting cells did not upregulate Hes5-GFP in the damaged cochlea. Therefore, absence of Notch-Hes5 signaling in the normal and damaged adult cochlea is correlated with lack of regeneration potential, while its presence in the neonatal cochlea and adult vestibular epithelia is associated with greater capacity for plasticity or regeneration in these tissues; which suggests that this pathway may be involved in regulating regenerative potential.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Blimp1 controls photoreceptor versus bipolar cell fate choice during retinal development. 20110327

    Photoreceptors, rods and cones are the most abundant cell type in the mammalian retina. However, the molecules that control their development are not fully understood. In studies of photoreceptor fate determination, we found that Blimp1 (Prdm1) is expressed transiently in developing photoreceptors. We analyzed the function of Blimp1 in the mouse retina using a conditional deletion approach. Developmental analysis of mutants showed that Otx2(+) photoreceptor precursors ectopically express the bipolar cell markers Chx10 (Vsx2) and Vsx1, adopting bipolar instead of photoreceptor fate. However, this fate shift did not occur until the time when bipolar cells are normally specified during development. Most of the excess bipolar cells died around the time of bipolar cell maturation. Our results suggest that Blimp1 expression stabilizes immature photoreceptors by preventing bipolar cell induction. We conclude that Blimp1 regulates the decision between photoreceptor and bipolar cell fates in the Otx2(+) cell population during retinal development.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Foxp4 is essential in maintenance of PURKINJE cell dendritic arborization in the mouse cerebellum. 20951773

    Purkinje cells (PCs) are one of the principal neurons in the cerebellar cortex that play a central role in the coordination of fine-tuning body movement and balance. To acquire normal cerebellum function, PCs develop extensive dendritic arbors that establish synaptic connections with the parallel fibers of granule cells to form the proper neuronal circuitry. Therefore, dendritic arborization of PCs is an important developmental step to construct the mature neural network in the cerebellum. However, the genetic control of this process is not fully understood. In this study, Foxp4, a forkhead transcription factor that is expressed specifically in migrating and mature PCs of cerebellum from embryonic stages to adulthood, was knocked down by small interfering RNA (siRNA) in organotypic cerebellar slice culture. When Foxp4 expression was knocked down at postnatal day 5 (P5), no abnormalities for early dendritic remodeling of PCs were observed. However, when Foxp4 was knocked down in P10 cerebellar slices, the organization of PC dendritic arbors was highly impaired, leaving hypoplastic but non-apoptotic cell bodies. The radial alignment of Bergmann glial fibers that associated with PC dendrites was also lost. These results suggest that Foxp4 is dispensable for the early PC dendrite outgrowth, but is essential for the maintenance of PC dendritic arborization and subsequent association with Bergmann glial fibers.
    Tipo de documento:
    Referencia
    Referencia del producto:
    AB1778

  • Caytaxin deficiency disrupts signaling pathways in cerebellar cortex. 17092653

    The genetically dystonic (dt) rat, an autosomal recessive model of generalized dystonia, harbors an insertional mutation in Atcay. As a result, dt rats are deficient in Atcay transcript and the neuronally-restricted protein caytaxin. Previous electrophysiological and biochemical studies have defined olivocerebellar pathways, particularly the climbing fiber projection to Purkinje cells, as sites of significant functional abnormality in dt rats. In normal rats, Atcay transcript is abundantly expressed in the granular and Purkinje cell layers of cerebellar cortex. To better understand the consequences of caytaxin deficiency in cerebellar cortex, differential gene expression was examined in dt rats and their normal littermates. Data from oligonucleotide microarrays and quantitative real-time reverse transcriptase-PCR (QRT-PCR) identified phosphatidylinositol signaling pathways, calcium homeostasis, and extracellular matrix interactions as domains of cellular dysfunction in dt rats. In dt rats, genes encoding the corticotropin-releasing hormone receptor 1 (CRH-R1, Crhr1) and plasma membrane calcium-dependent ATPase 4 (PMCA4, Atp2b4) showed the greatest up-regulation with QRT-PCR. Immunocytochemical experiments demonstrated that CRH-R1, CRH, and PMCA4 were up-regulated in cerebellar cortex of mutant rats. Along with previous electrophysiological and pharmacological studies, our data indicate that caytaxin plays a critical role in the molecular response of Purkinje cells to climbing fiber input. Caytaxin may also contribute to maturational events in cerebellar cortex.
    Tipo de documento:
    Referencia
    Referencia del producto:
    AB1778

  • Robo1 regulates the development of major axon tracts and interneuron migration in the forebrain. 16690755

    The Slit genes encode secreted ligands that regulate axon branching, commissural axon pathfinding and neuronal migration. The principal identified receptor for Slit is Robo (Roundabout in Drosophila). To investigate Slit signalling in forebrain development, we generated Robo1 knockout mice by targeted deletion of exon 5 of the Robo1 gene. Homozygote knockout mice died at birth, but prenatally displayed major defects in axon pathfinding and cortical interneuron migration. Axon pathfinding defects included dysgenesis of the corpus callosum and hippocampal commissure, and abnormalities in corticothalamic and thalamocortical targeting. Slit2 and Slit1/2 double mutants display malformations in callosal development, and in corticothalamic and thalamocortical targeting, as well as optic tract defects. In these animals, corticothalamic axons form large fasciculated bundles that aberrantly cross the midline at the level of the hippocampal and anterior commissures, and more caudally at the medial preoptic area. Such phenotypes of corticothalamic targeting were not observed in Robo1 knockout mice but, instead, both corticothalamic and thalamocortical axons aberrantly arrived at their respective targets at least 1 day earlier than controls. By contrast, in Slit mutants, fewer thalamic axons actually arrive in the cortex during development. Finally, significantly more interneurons (up to twice as many at E12.5 and E15.5) migrated into the cortex of Robo1 knockout mice, particularly in both rostral and parietal regions, but not caudal cortex. These results indicate that Robo1 mutants have distinct phenotypes, some of which are different from those described in Slit mutants, suggesting that additional ligands, receptors or receptor partners are likely to be involved in Slit/Robo signalling.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Ascl1 expression defines a subpopulation of lineage-restricted progenitors in the mammalian retina. 21771810

    The mechanisms of cell fate diversification in the retina are not fully understood. The seven principal cell types of the neural retina derive from a population of multipotent progenitors during development. These progenitors give rise to multiple cell types concurrently, suggesting that progenitors are a heterogeneous population. It is thought that differences in progenitor gene expression are responsible for differences in progenitor competence (i.e. potential) and, subsequently, fate diversification. To elucidate further the mechanisms of fate diversification, we assayed the expression of three transcription factors made by retinal progenitors: Ascl1 (Mash1), Ngn2 (Neurog2) and Olig2. We observed that progenitors were heterogeneous, expressing every possible combination of these transcription factors. To determine whether this progenitor heterogeneity correlated with different cell fate outcomes, we conducted Ascl1- and Ngn2-inducible expression fate mapping using the CreER™/LoxP system. We found that these two factors gave rise to markedly different distributions of cells. The Ngn2 lineage comprised all cell types, but retinal ganglion cells (RGCs) were exceedingly rare in the Ascl1 lineage. We next determined whether Ascl1 prevented RGC development. Ascl1-null mice had normal numbers of RGCs and, interestingly, we observed that a subset of Ascl1+ cells could give rise to cells expressing Math5 (Atoh7), a transcription factor required for RGC competence. Our results link progenitor heterogeneity to different fate outcomes. We show that Ascl1 expression defines a competence-restricted progenitor lineage in the retina, providing a new mechanism to explain fate diversification.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Population based quantification of dendrites: evidence for the lack of microtubule-associate protein 2a,b in Purkinje cell spiny dendrites. 20727947

    The high molecular weight isoforms (a and b) of microtubule-associate protein 2 (MAP2a,b) are widely believed to be specific markers for neuronal somata and dendrites. We analyzed and quantified MAP2a,b stained dendrites of the cerebellar molecular layer using a novel approach that segmented and 3D reconstructed them, and the results have been compared with those obtained by other methods, including single-cell reconstruction and analysis of electron micrographs. Our results show that the molecular layer dendritic volume fraction is lower than in the neocortex (10% compared to neocortical 29%). The low total volume fraction of dendrites in the molecular layer is best explained by the majority of the afferents to the dendrites being from the very densely packed parallel fibers, which allows the dendritic fields of individual neurons to be smaller and more compact than in the cerebral cortex. However, the MAP2a,b dendritic volume fraction is even lower (5.2%) than the total volume fraction of dendrites in the molecular layer (10%). Analysis of the material shows that this difference between the two results is due to the unexpected finding that there were few MAP2a,b stained Purkinje cell spiny dendrites.
    Tipo de documento:
    Referencia
    Referencia del producto:
    AB1778

  • Metabotropic glutamate receptors modulate the NMDA- and AMPA-induced gene expression in neocortical interneurons. 16407481

    Group I metabotropic glutamate receptors (mGluRIs) can be colocalized with ionotropic glutamate receptors in postsynaptic membranes. We have investigated whether mGluRIs alter the gene transcription induced by N-methyl-D-aspartate (NMDA) and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) receptors in rat neocortical gamma-aminobutyric acid (GABA) interneurons. In cultures of dissociated interneurons, the mGluRI antagonists LY367385 and MPEP reduced the increase in phosphorylation of the transcription factor CREB induced by NMDA as well as the expression of the proenkephalin (PEnk) gene. In contrast, they enhanced the AMPA-induced CREB phosphorylation and PEnk gene expression. Stimulation of the mGluRIs was due to network activity that caused the release of endogenous glutamate and could be blocked by tetrodotoxin. In organotypic cultures of neocortex, endogenous glutamate enhanced the PEnk gene expression by acting on NMDA and AMPA receptors. These effects were modulated via mGluRIs. In patch-clamp experiments and in biochemical studies on receptor density, stimulation of mGluRIs acutely affected NMDA receptor currents but had no long-term effect on NMDA receptor density at the cell surface. In contrast, stimulation of mGluRIs decreased the density of AMPA receptors located at the cell surface. Our results suggest that mGluRIs regulate the glutamate-induced gene expression in neocortical interneurons in a physiologically relevant manner.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Distribution of the parvalbumin, calbindin-D28K and calretinin immunoreactivity in globus pallidus of the Brazilian short-tailed opossum (Monodelphis domestica). 18320720

    This study describes the topography, borders and divisions of the globus pallidus in the Brazilian short-tailed opossum (Monodelphis domestica) and distribution of the three calcium binding proteins, parvalbumin (PV), calbindin D-28k (CB) and calretinin (CR) in that nucleus. The globus pallidus of the opossum consists of medial and lateral parts that are visible with Nissl or Timm's staining and also in PV and CR immunostained sections. Neurons of the globus pallidus expressing these proteins were classified into three types on the basis of size and shape of their soma and dendritic tree. Type 1 neurons had medium-sized fusiform soma with dendrites sprouting from the opposite poles. Neurons of the type 2 had medium-to-large, multipolar soma with scarce, thin dendrites. Cell bodies of type 3 neurons were small and either ovoid or round. Immunostaining showed that the most numerous were neurons expressing PV that belonged to all three types. Density of the PV-immunopositive fibers and puncta correlated with the density of the PV-labeled neurons. Labeling for CB resulted mainly in the light staining of neuropil in both parts of the nucleus, while the CB-expressing cells (mainly of the type 2) were scarce and placed only along the border of the globus pallidus and putamen. Staining for calretinin resulted in labeling almost exclusively the immunoreactive puncta and fibers that were distributed with medium-to-high density throughout the nucleus. Close to the border of globus pallidus with the putamen these fibers (probably dendrites) were long, thin and varicous, while more medially bundles of thick, short and smooth fibers predominated. Single CR-ir neurons (all of the type 3) were scattered through the globus pallidus. Colocalization of two calcium binding proteins in one neuron was. never observed. The CB-ir puncta (probably terminals of axons projecting to the nucleus) frequently formed basket-like structures around the PV-ir neurons. Therefore, the globus pallidus in the opossum, much as that in the rat, consists of a heterogeneous population of neurons, probably playing diversified functions.
    Tipo de documento:
    Referencia
    Referencia del producto:
    AB5054