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PubMed1999

Functional analysis of DNA sequences located within a cluster of DNase I hypersensitive sites colocalizing with a MAR element at the upstream border of the chicken alpha-globin gene domain.

We have cloned and sequenced a genomic DNA fragment of chicken containing a cluster of DNase I hypersensitive sites (DHS) located 11-15 kb upstream from the first gene of the alpha-globin gene domain and including a constitutive DHS flanked by two erythroid-specific ones. A 1.2-kb subfragment of the DNA fragment under study located upstream to the constitutive DHS and colocalizing roughly with one of the erythroid-specific DHS was shown to possess the properties of a matrix association region (MAR). The cloned DNA sequences were tested for their ability to serve as promoters and/or influence transcription from the promoter of the alphaD globin gene. In the region studied, we did not find any promoters or enhancers that were active in erythroid cells. The whole DNase I hypersensitive region and some of its subfragments showed a silencing effect when placed downstream from the reporter gene. The expression of the reporter gene was completely abolished, however, when these DNA fragments were placed between the alphaD promoter and the reporter gene. Thus, they seem to act as transcription "terminators." Numerous polyadenylation signals (AATAAA) and an AT-rich palindrome were found within the sequenced DNA fragment. These observations are discussed within the frame of the hypothesis postulating that continuous transcription is essential for maintaining the active status of genomic domains. Furthermore, it is suggested that the DNA fragment studied contains a negative control element that keeps globin genes silent within the chromatin domain permanently open in nonerythroid cells.

Animals↗
PubMed2004

Patterns of colocalization of neuronal nitric oxide synthase and somatostatin-like immunoreactivity in the mouse hippocampus: quantitative analysis with optical disector.

In some brain regions, previous studies reported the frequent coexistence between neuronal nitric oxide synthase (nNOS) and somatostatin (SOM). In the hippocampus, nNOS and SOM were mainly expressed in GABAergic nonprincipal neurons. Here we estimated the immunocytochemical colocalization of nNOS and SOM in the mouse hippocampus using the optical disector. Both in the Ammon's horn and dentate gyrus, we encountered only a few nNOS-immunoreactive (IR)/SOM-like immunoreactive (LIR) neurons. They were mainly located in the stratum oriens of the Ammon's horn and in the dentate hilus. The nNOS-IR/SOM-LIR neurons usually showed characteristic large somata with thick dendrites, whereas the majority of nNOS-IR/SOM-negative neurons showed small somata with thin dendrites. Quantitative data revealed that the double-labeled cells represented only 4% and 7% of nNOS-IR neurons and SOM-LIR neurons, respectively, in the whole area of the hippocampus. We also found the laminar and dorsoventral differences in the degree of colocalization between nNOS and SOM. The percentages of nNOS-IR neurons containing SOM-like immunoreactivity were relatively high in the stratum oriens of the ventral CA1 region (24%), stratum lucidum of the dorsal CA3 region (29%) and dorsal dentate hilus (32%), but they were quite low in the other layers. On the other hand, the percentages of SOM-LIR neurons containing nNOS immunoreactivity were somewhat high in the stratum lucidum of the dorsal CA3 region (19%) and dorsal dentate hilus (28%), whereas they were very low in the other layers. Immunofluorescent triple labeling of axon terminals for nNOS, SOM and glutamic acid decarboxylase indicated that some nNOS-IR/SOM-LIR neurons might be dendritic inhibitory cells. The present results show the infrequent colocalization of nNOS and SOM in the mouse hippocampus, and also suggest that the double-labeled cells may be a particular subpopulation of hippocampal GABAergic nonprincipal neurons.

Animals↗
PubMed2002

Osteoblast intracellular localization of Nmp4 proteins.

Nmp4 proteins are transcription factors that contribute to the expression of type I collagen and many of the matrix metalloproteinase genes. Numerous Nmp4 isoforms have been identified. These proteins, all derived from a single gene, have from five to eight Cys(2)His(2) zinc fingers, the arrangement of which directs specific isoforms to nuclear matrix subdomains. Nmp4 isoforms also have an SH3 binding domain, typical of cytoplasmic docking proteins. Although recent evidence indicates that Nmp4 proteins also reside in the osteoblast cytoplasm, whether they localize to specific organelles or structures is not well defined. The intracellular localization of a protein is a determinant of its function and provides insights into its mechanism of action. As a first step toward determining the functional relationship between the cytoplasmic and nuclear Nmp4 compartments, we mapped their location in the osteoblast cytoplasm. Immunocytochemical analysis of osteoblasts demonstrated that Nmp4 antibodies labeled the mitochondria, colocalized with Golgi protein 58K, and lightly stained the cytoplasm. Western analysis using Nmp4 antibodies revealed a complex profile of protein bands in the nuclear, mitochondrial, and cytosolic fractions. Several of these proteins were specific to defined intracellular domains. Consistent with the western analyses, reverse transcription-polymerase chain reaction (RT-PCR) analysis detected previously uncharacterized Nmp4 isoforms. These data necessarily enlarge the known Nmp4 family from nuclear matrix transcription factors to a more widely extended class of intracellular proteins.

3T3 Cells↗
PubMed2002

Colocalization of intracellular osteopontin with CD44 is associated with migration, cell fusion, and resorption in osteoclasts.

Although osteopontin (OPN) is recognized generally as a secreted protein, an intracellular form of osteopontin (iOPN), associated with the CD44 complex, has been identified in migrating fibroblastic cells. Because both OPN and CD44 are expressed at high levels in osteoclasts, we have used double immunofluorescence analysis and confocal microscopy to determine whether colocalization of these proteins has functional significance in the formation and activity of osteoclasts. Analysis of rat bone marrow-derived osteoclasts revealed strong surface staining for CD44 and beta1- and beta3-integrins, whereas little or no staining for OPN or bone sialoprotein (BSP) was observed in nonpermeabilized cells. In permeabilized perfusion osteoclasts and multinucleated osteoclasts, staining for OPN and CD44 was prominent in cell processes, including filopodia and pseudopodia. Confocal microscopy revealed a high degree of colocalization of OPN with CD44 in motile osteoclasts. In cells treated with cycloheximide (CHX), perinuclear staining for OPN and BSP was lost, but iOPN staining was retained within cell processes. In osteoclasts generated from the OPN-null and CD44-null mice, cell spreading and protrusion of pseudopodia were reduced and cell fusion was impaired. Moreover, osteoclast motility and resorptive activity were significantly compromised. Although the area resorbed by OPN-null osteoclasts could be rescued partially by exogenous OPN, the resorption depth was not affected. These studies have identified an intracellular form of OPN, colocalizing with CD44 in cell processes, that appears to function in the formation and activity of osteoclasts.

Animals↗
PubMed2005

Dysferlin interacts with affixin (beta-parvin) at the sarcolemma.

The dysferlin gene is defective in Miyoshi myopathy (MM) and limb girdle muscular dystrophy type 2B (LGMD2B). Dysferlin is a sarcolemmal protein that is implicated in calcium-dependent membrane repair. Affixin (beta-parvin) is a novel, integrin-linked kinase-binding protein that is involved in the linkage between integrin and the cytoskeleton. Here we show that affixin is a dysferlin binding protein that colocalizes with dysferlin at the sarcolemma of normal human skeletal muscle. The immunoreactivity of affixin was reduced in sarcolemma of MM and LGMD2B muscles, although the total amount of the affixin protein was normal. Altered immunoreactivity of affixin was also observed in other muscle diseases including LGMD1C, where both affixin and dysferlin showed quite similar changes with a reduction of sarcolemmal staining with or without cytoplasmic accumulations. Colocalization of dysferlin and affixin was confirmed by immunofluorescence analysis using dysferlin-expressing C2 myoblasts. Wild-type and mutant dysferlin colocalized with endogenous affixin. The interaction of dysferlin and affixin was confirmed by immunoprecipitation study using normal human and mouse skeletal muscles. Using immunoprecipitation with deletion mutants of dysferlin, we have identified that C-terminal region of dysferlin is an apparent binding site for affixin. We also found N-terminal calponin homology domain of affixin as a binding site for dysferlin. Our results suggest that affixin may participate in membrane repair with dysferlin.

Actinin↗
PubMed2004

Ionizing radiation-induced instant pairing of heterochromatin of homologous chromosomes in human cells.

Using fluorescence in situ hybridization with human band-specific DNA probes we examined the effect of ionizing radiation on the intra-nuclear localization of the heterochromatic region 9q12-->q13 and the euchromatic region 8p11.2 of similar sized chromosomes 9 and 8 respectively in confluent (G1) primary human fibroblasts. Microscopic analysis of the interphase nuclei revealed colocalization of the homologous heterochromatic regions from chromosome 9 in a proportion of cells directly after exposure to 4 Gy X-rays. The percentage of cells with paired chromosomes 9 gradually decreased to control levels during a period of one hour. No significant changes in localization were observed for chromosome 8. Using 2-D image analysis, radial and inter-homologue distances were measured for both chromosome bands. In unexposed cells, a random distribution of the chromosomes over the interphase nucleus was found. Directly after irradiation, the average inter-homologue distance decreased for chromosome 9 without alterations in radial distribution. The percentage of cells with inter-homologue distance <3 micro m increased from 11% in control cells to 25% in irradiated cells. In contrast, irradiation did not result in significant changes in the inter-homologue distance for chromosome 8. Colocalization of the heterochromatic regions of homologous chromosomes 9 was not observed in cells irradiated on ice. This observation, together with the time dependency of the colocalization, suggests an underlying active cellular process. The biological relevance of the observed homologous pairing remains unclear. It might be related to a homology dependent repair process of ionizing radiation induced DNA damage that is specific for heterochromatin. However, also other more general cellular responses to radiation-induced stress or change in chromatin organization might be responsible for the observed pairing of heterochromatic regions.

Adult↗
PubMed2006

NG2 colocalizes with axons and is expressed by a mixed cell population in spinal cord lesions.

The NG2 proteoglycan is of general interest after spinal cord injury because it is expressed by oligodendrocyte progenitors (OPCs), which contribute to central nervous system remyelination; however, NG2 may inhibit axon regeneration. We and others have examined the spatiotemporal expression of NG2 after spinal cord injury (SCI). Here, we extend those observations and provide a comprehensive analysis of the distribution, phenotype, and colocalization of NG2 cells with axons in a clinically relevant model of spinal contusion. Because contusion models mimic the majority of human SCI, this information is important for understanding endogenous processes that promote and/or prevent repair. The data demonstrate that NG2 levels rise significantly between 3 and 7 days postinjury (dpi) and remain elevated chronically throughout the lesions. NG2 within the lesions could be derived from an array of infiltrating cells; thus, a panel of antibodies was used to investigate NG2 cell phenotypes. First, platelet-derived growth factor-alpha receptor (PDGFalphaR) colocalization was examined because OPCs normally express both markers. PDGFalphaR cells were present in lesions at all times examined. However, only 37% of NG2 cells coexpressed PDGFalphaR at 14 dpi, which dropped to <1% by 70 dpi. This contrasts with the nearly complete overlap in spared tissue surrounding the lesion. In contrast, 40% to 60% of NG2 cells expressed p75 and approximately 84% expressed Sox10, suggesting that many NG2 cells were nonmyelinating Schwann cells. Despite rising levels of NG2, we noted robust and sustained axon growth into the lesions, many of which were located along NG2 profiles. Thus, spinal contusion produces an NG2-rich environment into which axons grow and in which the source of NG2 appears considerably different from that in surrounding spared tissue.

Animals↗
PubMed2003

Colocalization of muscle FBPase and muscle aldolase on both sides of the Z-line.

Previously we have reported that in vitro muscle aldolase binds to muscle FBPase [Biochem. Biophys. Res. Commun. 275 (2000) 611-616] which results in the changes of regulatory properties of the latter enzyme. In the present paper, the evidence that aldolase binds to FBPase in living cell is presented. The colocalization experiment, in which aldolase was diffused into skinned fibres that had been pre-incubated with FBPase, has shown that aldolase in the presence of FBPase binds predominantly to the Z-line. The existence of a triple aldolase-FBPase-alpha-actinin complex was confirmed through a real-time interaction analysis using the BIAcore biosensor. The colocalization of FBPase and aldolase on alpha-actinin of the Z-line indicates the existence of glyconeogenic metabolon in vertebrates' myocytes.

Actinin↗
PubMed2005

Combining data from multiple inbred line crosses improves the power and resolution of quantitative trait loci mapping.

Rodent inbred line crosses are widely used to map genetic loci associated with complex traits. This approach has proven to be powerful for detecting quantitative trait loci (QTL); however, the resolution of QTL locations, typically approximately 20 cM, means that hundreds of genes are implicated as potential candidates. We describe analytical methods based on linear models to combine information available in two or more inbred line crosses. Our strategy is motivated by the hypothesis that common inbred strains of the laboratory mouse are derived from a limited ancestral gene pool and thus QTL detected in multiple crosses are likely to represent shared ancestral polymorphisms. We demonstrate that the combined-cross analysis can improve the power to detect weak QTL, can narrow support intervals for QTL regions, and can be used to separate multiple QTL that colocalize by chance. Moreover, combined-cross analysis can establish the allelic states of a QTL among a set of parental lines, thus providing critical information for narrowing QTL regions by haplotype analysis.

Cholesterol, HDL↗
PubMed2000

Human CLP36, a PDZ-domain and LIM-domain protein, binds to alpha-actinin-1 and associates with actin filaments and stress fibers in activated platelets and endothelial cells.

A 38-kd protein that associates with F-actin structures in activated platelets and endothelial cells was purified, cloned, and characterized. The protein contains an N-terminal PDZ motif, a large intervening sequence, and a C-terminal LIM domain and was identified as the human homolog of rat CLP36. The study showed that CLP36 associates with actin filaments and stress fibers that are formed during shape change and spreading of platelets and during migration and contraction of endothelial cells. CLP36 binds to alpha-actinin-1 as shown by coimmunoprecipitation, pull-down experiments, yeast 2-hybrid analysis, and blot overlay assays and colocalizes with alpha-actinin-1 along endothelial actin stress fibers. In contrast to alpha-actinin-1, CLP36 was absent from focal adhesions in both activated platelets and endothelial cells. The N-terminal part of CLP36 containing the PDZ domain and the intervening region, but not the LIM domain, targeted enhanced green fluorescent protein fusion proteins to stress fibers in endothelial cells. Yeast 2-hybrid analysis demonstrated that the intervening sequence, but not the PDZ or the LIM domain of CLP36, binds to the spectrinlike repeats 2 and 3 of alpha-actinin-1. The study further shows that CLP36 binds to alpha-actinin in resting platelets and translocates as a CLP36/alpha-actinin complex to the newly formed actin cytoskeleton in activated platelets. The results indicate that CLP36 binds via alpha-actinin-1 to actin filaments and stress fibers in activated human platelets and endothelial cells. The study suggests that CLP36 may direct alpha-actinin-1 to specific actin structures and at this position might modulate the function of alpha-actinin-1. (Blood. 2000;96:4236-4245)

Actin Cytoskeleton↗
PubMed2004

Structural and biomolecular changes in aorta and pulmonary trunk of patients with aortic aneurysm and valve disease: implications for the Ross procedure.

OBJECTIVES: A higher incidence of pulmonary autograft dilatation is assumed in patients with ascending aortic dilatation and bicuspid aortic valve disease. To examine whether structural abnormalities are present in the ascending aorta as well as in the pulmonary trunk (PT) we specifically addressed molecular mechanisms and signalling pathways for aneurysm formation in ascending aortic aneurysms and PT of patients with different aortic valve pathology undergoing an extended Ross procedure. METHODS: Wall segments resected from aortic aneurysms (20 patients, 7 bicuspid aortic valves BAV, and 13 tricuspid aortic valves TAV) and from PTs were submitted to analysis of leukocyte infiltration (immunohistochemistry), smooth muscle cell (SMC) apoptosis (in situ end-labelling of DNA-fragments TUNEL), and expression of death-promoting proteins perforin, granzyme B, Fas/FasL (immunoblotting). RESULTS: Degenerative changes including rarefication and apoptosis of SMCs were significantly more severe in BAV than TAV disease (apoptotic index 9.2+/-3.2 vs. 11.9+/-6.2, P = 0.02). Immunohistochemistry confirmed presence and activation of death-promoting mediators in aneurysmal tissue whereas pulmonary tissue displayed only few apoptotic cells, occasional Fas+cells, rarely colocalized with FasL. By Western blot analysis extracts from BAV and TAV but not pulmonary artery wall contained appreciable amounts of perforin, granzyme B, and Fas/FasL. CONCLUSION: Aneurysm formation is associated with SMC apoptosis and local signal expression of activated cells in patients with bicuspid as well as TAV. The PT itself is not pathologically involved with only minor degenerative changes. Although the disease process in the aorta appeared to be more severe in patients with BAV, there was similarity of histological and molecular changes of the pulmonary artery wall in all patients. Dilation of the pulmonary autograft seems not to be the result of histopathological and biomolecular mechanisms in the PT.

Adolescent↗
PubMed1992

Adenovirus L1 52- and 55-kilodalton proteins are present within assembling virions and colocalize with nuclear structures distinct from replication centers.

Analysis of a temperature-sensitive mutant, Ad5ts369, had indicated that the adenovirus L1 52- and 55-kDa proteins (52/55-kDa proteins) are required for the assembly of infectious virions. By using monoclonal antibodies directed against bacterially produced L1 52-kDa protein, the L1 52/55-kDa proteins were found to be differentially phosphorylated forms of a single 48-kDa polypeptide. Both phosphoforms were shown to be present within all suspected virus assembly intermediates (empty capsids, 50 to 100 molecules; young virions, 1 to 2 molecules) but not within mature virions. The mobilities of these proteins in polyacrylamide gels were affected by reducing agents, indicating that the 52/55-kDa proteins may exist as homodimers within the cell and within assembling particles. Immunofluorescence analysis revealed that the 52/55-kDa proteins localize to regions within the infected nucleus that are distinct from viral DNA replication centers, indicating that replication and assembly of viral components likely occur in separate nuclear compartments. Immunoelectron microscopic studies determined that the 52/55-kDa proteins are found in close association with structures that appear to contain assembling virions. These results are consistent with an active but transient role for the L1 products in assembly of the adenovirus particle, perhaps as scaffolding proteins.

Adenoviridae↗
PubMed1999

Transient coexpression of nestin, GFAP, and vascular endothelial growth factor in mature reactive astroglia following neural grafting or brain wounds.

The spatial and temporal immunoexpression of the intermediate filament (IF) protein nestin and its relationship to glial fibrillary acidic protein (GFAP), vascular endothelial growth factor (VEGF), and its receptor flt-1 (VEGF-R1) in reactive astroglia was examined following stab wounds or transplants of fetal CNS tissue into the adult brain. Since developmentally regulated proteins and gene transcripts can be reexpressed in reactive astroglia following certain brain injuries, we analyzed the nestin profile in these experimental paradigms in order to more fully understand the nature of the gliotic "scar." Nestin expression was transiently up-regulated in some but not all astrocytes which often had a different morphology than the typical stout, stellate GFAP (+) cells; the processes of the nestin (+) cells tended to be slender and elongated. In reactive astroglia from the mature brain, nestin expression was robust but generally localized to the wound or graft site, peaked at 7-10 days postoperative, and was absent by 28 days, whereas GFAP (+) astrocytes were far more widespread and persisted for many months. Only nestin was strongly expressed immediately adjacent to early stab wounds, whereas GFAP (+) cells were located further from the wound sites. In contrast, there was marked nestin/GFAP colocalization at the graft/host interface. Semiquantitative analysis combined with confocal microscopy revealed a unique compartmentalization of protein expression; processes from single astrocytes could be entirely nestin (+), GFAP (+), or could show coexpression. At 4, 7, and 14 days postoperative, 41, 58, and 32% of the immunoexpression, respectively, was accounted for by nestin at the graft/host interface, and it was essentially undetectable at 28 days postoperative. In situ hybridization studies showed nestin transcripts within GFAP (+) cells primarily between 4 and 10 days postoperative and absent by 28 days. Many nestin (+) astrocytes, as shown by electron microscopy, were closely related to the vasculature. Therefore we further examined the expression of vascular endothelial growth factor (VEGF), an endothelial cell mitogen associated with angiogenesis. Nestin colocalized with VEGF in some astrocytes (7%) but far more prominently with the VEGF flt-1 receptor (25%). Early astroglial activation may involve several different IF components and possibly a distinct astrocytic population that shows a rapid, transient nestin expression adjacent to injury sites. Expression of the nestin IF phenotype within affected astrocytes in the surgical vicinity may be indicative of a reversion to an immature phenotype that might be less susceptible to attendant hypoxia after injury. Since injured astrocytes are well known to express many bioactive compounds, such transient reexpression of early, developmentally regulated proteins may be a hallmark for the elaboration of growth factors such as VEGF.

Animals↗
PubMed2006

Functional domains of murine cytomegalovirus nuclear egress protein M53/p38.

Two conserved herpes simplex virus 1 proteins, UL31 and UL34, form a complex at the inner nuclear membrane which governs primary envelopment and nuclear egress of the herpesvirus nucleocapsids. In mouse cytomegalovirus, a member of the betaherpesvirus subfamily, the homologous proteins M53/p38 and M50/p35 form the nuclear egress complex (NEC). Since the interaction of these proteins is essential for functionality, the definition of the mutual binding sites is a prerequisite for further analysis. Using a comprehensive random mutagenesis procedure, we have mapped the M53/p38 binding site of M50/p35 (A. Bubeck, M. Wagner, Z. Ruzsics, M. Lötzerich, M. Iglesias, I. R. Singh, and U. H. Koszinowski, J. Virol. 78:8026-8035). Here we describe a corresponding analysis for the UL31 homolog M53/p38. A total of 72 individual mutants were reinserted into the genome to test the complementation of the lethal M53 null phenotype. The mutants were also studied for colocalization and for coprecipitation with M50/p35. The analysis revealed that the nonconserved N-terminal one-third of M53/p38 provides the nuclear localization signal as an essential function. The collective results for many mutants localized the binding site for M50/p35 to amino acids (aa) 112 to 137. No single aa exchange for alanine could destroy NEC formation, but virus attenuation revealed a major role for aa K128, Y129, and L130. The lethal phenotype of several insertion and stop mutants indicated the functional importance of the C terminus of the protein.

Animals↗
PubMed2000

Injury-specific expression of activating transcription factor-3 in retinal ganglion cells and its colocalized expression with phosphorylated c-Jun.

PURPOSE: To ascribe activating transcription factor (ATF)-3 as a specifically induced transcription factor after ON injury and to describe its putative role as a modulator of c-Jun transactivation. METHODS: The adult rat optic nerve was crushed intraorbitally, and expression profiles of ATF-3, ATF-2, and phosphorylated c-Jun (p-c-Jun) were examined by immunohistochemistry and ISH. Western blot analysis for ATF-3 and -2 were also performed. Furthermore, colocalized detection of c-Jun mRNA with ATF-2 or -3 was attempted with a combined method of simultaneous immunohistochemistry and in situ hybridization. RESULTS: In response to optic nerve injury, substantial expression of ATF-3 as well as that of p-c-Jun was observed in the retinal ganglion cells, whereas no expression of ATF-3 was seen in other noninjured retinal cells. In contrast, ATF-2 was normally expressed abundantly in both retinal ganglion cells and displaced amacrine cells, but expression dropped in retinal ganglion cells after nerve injury. The expression profiles of ATF-2 and -3 after optic nerve injury were confirmed by Western blot analysis. A higher degree of colocalization was observed for ATF-3 and c-Jun than the modest codetection for ATF-2 and c-Jun. CONCLUSIONS: The transcription factor ATF-3 is specifically induced upon optic nerve injury and colocalizes with p-c-Jun in surviving ganglion cells. These findings suggest that both ATF-3 and c-Jun are crucial to trigger various transcriptional responses and may act synergistically during the survival phase of the optic nerve in the injury model.

Activating Transcription Factor 2↗
PubMed2003

Neuronal glutamate transporter EAAT4 is expressed in astrocytes.

High-affinity excitatory amino acid transporters (EAATs) are essential to terminate glutamatergic neurotransmission and to prevent excitotoxicity. To date, five distinct EAATs have been cloned from animal and human tissues: GLAST (EAAT1), GLT-1 (EAAT2), EAAC1 (EAAT3), EAAT4, and EAAT5. EAAT1 and EAAT2 are commonly known as glial glutamate transporters, whereas EAAT3, EAAT4, and EAAT5 are neuronal. EAAT4 is largely expressed in cerebellar Purkinje cells. In this study, using immunohistochemistry and Western blotting, we found that EAAT4-like immunoreactivity (ir) is enriched in the spinal cord and forebrain. Double-labeled fluorescent immunostaining and confocal image analysis indicated that EAAT4-like ir colocalizes with an astrocytic marker, glial fibrillary acidic protein (GFAP). The astrocytic localization of EAAT4 was further confirmed in astrocyte cultures by double-labeled fluorescent immunocytochemistry and Western blotting. Reverse transcriptase-polymerase chain reaction analysis demonstrated mRNA expression of EAAT4 in astrocyte cultures. Sequencing confirmed the specificity of the amplified fragment. These results demonstrate that EAAT4 is expressed in astrocytes. This astrocytic localization of neuronal EAAT4 may reveal a new function of EAAT4 in the central nervous system.

Amino Acid Transport System X-AG↗
PubMed2000

Developmental expression and assembly of connexins into homomeric and heteromeric gap junction hemichannels in the mouse mammary gland.

During the development of the mammary gland, duct-lining epithelial cells progress through a program of expansive proliferation, followed by a terminal differentiation that allows for the biosynthesis and secretion of milk during lactation. The role of gap junction proteins, connexins, in the development and function of this secretory epithelium was investigated. Connexins, Cx26 and Cx32, were differentially expressed throughout pregnancy and lactation in alveolar cells. Cx26 poly-(A)(+) RNA and protein levels increased from early pregnancy, whereas Cx32 was detectable only during lactation. At this time, immunolocalization of connexins by confocal microscopy and immunogold labeling of high-pressure frozen freeze-substituted tissue showed that both connexins colocalized to the same junctional plaque. Analysis of gap junction hemichannels (connexons) isolated from lactating mammary gland plasma membranes by a rate-density centrifugation procedure, followed by immunoprecipitation and by size-exclusion chromatography, showed that Cx26 and Cx32 were organized as homomeric and heteromeric connexons. Structural diversity in the assembly of gap junction hemichannels demonstrated between pregnant and lactating mammary gland may account for differences in ionic and molecular signaling that may physiologically influence the onset and/or maintenance of the secretory phenotype of alveolar epithelial cells.

Animals↗
PubMed2002

Subcellular localization of the BRCA1 gene product in mitotic cells.

The product of the hereditary breast cancer susceptibility gene BRCA1 is a multifunctional protein involved in the maintenance of genomic integrity, in transcriptional coactivation, and in the control of cell growth. BRCA1-deficient cells manifest chromosomal instability. During mitosis, BRCA1 is known to interact with gamma-tubulin in the centrosomes, key elements of the mitotic spindle. Using confocal microscopy and immunogold electron microscopy, we investigated the distribution of endogenous BRCA1 relative to mitotic spindle markers in breast cancer cells. By confocal analysis, BRCA1 and beta-tubulin colocalized to microtubules of the mitotic spindle and to the centrosomes. Immunogold electron microscopy confirmed these results and further revealed that BRCA1 and alpha-tubulin codistributed to the walls of the centrioles and to pericentriolar fibers at centrosomes. During chromatid segregation, codistribution was also detected along individual spindle microtubules and at sites of insertion of microtubules on chromosomes. At cytokinesis, BRCA1 and alpha-tubulin codistributed to the midbody. Coimmunoprecipitation supported the association of full-length BRCA1 with alpha- and beta-tubulin. These results are consistent with an involvement of BRCA1 in the dynamics of the mitotic spindle and in the segregation of duplicated chromosomes.

BRCA1 Protein↗