PubMed Health⌕ Search

Biomedical subjects

A Prescott

Publications and source records attributed to A Prescott.

At least 19 recordsLinked to original sources
PubMed2003

Using a pericentromeric interspersed repeat to recapitulate the phylogeny and expansion of human centromeric segmental duplications.

Despite considerable advances in sequencing of the human genome over the past few years, the organization and evolution of human pericentromeric regions have been difficult to resolve. This is due, in part, to the presence of large, complex blocks of duplicated genomic sequence at the boundary between centromeric satellite and unique euchromatic DNA. Here, we report the identification and characterization of an approximately 49-kb repeat sequence that exists in more than 40 copies within the human genome. This repeat is specific to highly duplicated pericentromeric regions with multiple copies distributed in an interspersed fashion among a subset of human chromosomes. Using this interspersed repeat (termed PIR4) as a marker of pericentromeric DNA, we recovered and sequence-tagged 3 Mb of pericentromeric DNA from a variety of human chromosomes as well as nonhuman primate genomes. A global evolutionary reconstruction of the dispersal of PIR4 sequence and analysis of flanking sequence supports a model in which pericentromeric duplications initiated before the separation of the great ape species (>12 MYA). Further, analyses of this duplication and associated flanking duplications narrow the major burst of pericentromeric duplication activity to a time just before the divergence of the African great ape and human species (5 to 7 MYA). These recent duplication exchange events substantially restructured the pericentromeric regions of hominoid chromosomes and created an architecture where large blocks of sequence are shared among nonhomologous chromosomes. This report provides the first global view of the series of historical events that have reshaped human pericentromeric regions over recent evolutionary time.

Animals↗
PubMed2002

F-MuLV acceleration of myelomonocytic tumorigenesis in SV40 large T antigen transgenic mice is accompanied by retroviral insertion at Fli1 and a novel locus, Fim4.

We describe here the development of a murine system for the identification of genes involved in myelomonocytic neoplasms. Transgenic C57BL/6J mice expressing SV40 early region under a myelomonocytic promoter develop histiocytic sarcomas with a latency of 167 days. We used retroviral proviral tagging to accelerate tumorigenesis and to uncover genetic changes that contribute to tumor development. Infection of transgenic mice with Friend murine leukemia virus (F-MuLV) shortened the latency of morbidity to 103 days (P< 0.001); this was associated with clonal proviral integrations in tumor DNA. As expected for F-MuLV, proviral insertions occurred at Fli1 in both transgenic and nontransgenic tumors. Four insertions were found at a novel locus, termed Fim4, on chromosome 6. This region is syntenic to human 7q32, a region that is commonly deleted in human myelodysplastic syndrome and acute myeloid leukemia. A murine BAC containing Fim4 was sequenced and analyzed, and while there was significant human-mouse homology in the area of the insertions, no candidate gene has been identified. Thus we have established a system to identify genes involved in myelomonocytic tumors, and have used it to identify Fim4, a new common site of proviral insertion. Study of this locus may provide insight into genes involved in AML-associated 7q32 deletions in humans.

Animals↗
PubMed2001

An essential role for calmodulin in regulating human T cell aggregation.

After activation of T cells with either CD3 antibodies or phorbol esters, we have found that T cell-cell aggregation, integrin-dependent actin reorganisation and cell spreading are strongly suppressed by any of three structurally different calmodulin antagonists, without any effect on the amount of CD11/CD18 integrin binding to the actin cytoskeleton. However, only T cell receptor-induced, and not phorbol ester-induced, aggregation and cell spreading are prevented by inhibitors of phosphatidylinositide (PI) 3-kinase. These results suggest that PI 3-kinase lies upstream of calmodulin in the signalling pathway leading to T cell aggregation, cell spreading and actin reorganisation and that cell spreading and actin reorganisation are essential for T cell adhesion.

Actins↗
PubMed2001

Antagonistic action of Six3 and Prox1 at the gamma-crystallin promoter.

Gamma-crystallin genes are specifically expressed in the eye lens. Their promoters constitute excellent models to analyse tissue-specific gene expression. We investigated murine CRYGE/f promoters of different length in lens epithelial cell lines. The most active fragment extends from position -219 to +37. Computer analysis predicts homeodomain and paired-domain binding sites for all rodent CRYGD/e/f core promoters. As examples, we analysed the effects of Prox1 and Six3, which are considered important transcription factors involved in lens development. Because of endogenous Prox1 expression in N/N1003A cells, a weak stimulation of CRYGE/f promoter activity was found for PROX1. In contrast, PROX1 stimulated the CRYGF promoter 10-fold in CD5A cells without endogenous PROX1. In both cell lines Six3 repressed the CRYGF promoter to 10% of its basal activity. Our cell transfection experiments indicated that CRYG expression increases as Six3 expression decreases. Prox1 and Six3 act antagonistically on regulation of the CRYGD/e/f promoters. Functional assays using randomly mutated gammaF-crystallin promoter fragments define a Six3-responsive element between -101 and -123 and a Prox1-responsive element between -151 and -174. Since Prox1 and Six3 are present at the beginning of lens development, expression of CRYGD/e/f is predicted to remain low at this time. It increases as Six3 expression decreases during ongoing lens development.

3T3 Cells↗
PubMed2000

Rapid induction of apoptosis mediated by peptides that bind initiation factor eIF4E.

Overexpression of the translation initiation factor eIF4E leads to cell transformation and occurs in a number of human cancers [1]. mRNA translation and cell growth can be regulated through the availability of eIF4E to form initiation complexes by binding to eIF4G. The availability of eIF4E is blocked through the binding of members of a family of eIF4E-binding proteins (4E-BPs) [2] [3]. Indeed, cell transformation caused by the overexpression of eIF4E can be reversed by the overexpression of 4E-BPs [4] [5] [6] [7] [8]. To study the role of eIF4E in cell transformation, we developed a series of peptides based on the conserved eIF4E-binding motifs in 4E-BPs and eIF4G [9] linked to the penetratin peptide-carrier sequence, which mediates the rapid transport of peptides across cell membranes. Surprisingly, introduction of these eIF4E-binding peptides into MRC5 cells led to rapid, dose-dependent cell death, with characteristics of apoptosis. Single alanine substitutions at key positions in the peptides impair their binding to eIF4E and markedly reduce their ability to induce apoptosis. A triple alanine substitution, which abolishes binding to eIF4E, renders the peptide unable to induce apoptosis. Our data provide strong evidence that the peptides induce apoptosis through binding to eIF4E. They do not induce apoptosis through inhibition of protein synthesis, as chemical inhibitors of translation did not induce apoptosis or affect peptide-induced cell death. Thus these new data indicate that eIF4E has a direct role in controlling cell survival that is not linked to its known role in mRNA translation.

Adaptor Proteins, Signal Transducing↗
PubMed2000

The veridicality of punitive childhood experiences reported by adolescents and young adults.

OBJECTIVE: The primary goal of the present research was to determine whether retrospective reports of childhood disciplinary experiences and perceptions of that discipline correspond to actual childhood events and whether the accuracy of that report was influenced by the affective state of the respondent. METHOD: Eighty-three adolescent and young adult males completed a retrospective measure of physical child maltreatment, Assessing Environments (AEIII), and the Brief Symptom Inventory (BSI). As children the participants had been observed naturalistically in their homes interacting with their parents an average of 10 years earlier. RESULTS: Analyses were consistent with the hypothesis that both current mood and actual observations of parent-child interactions during childhood predict self-reported recollections of childhood maltreatment by one's parents. Further the veridicality of such recollections appears to depend upon the objective specificity versus the perceptive nature of the questions used to elicit the recollections. CONCLUSIONS: The findings suggest that assessment instruments suitable for obtaining information regarding earlier childhood victimization must utilize behaviorally specific items. Thus, items that are either global or intimate a normative comparison should be avoided.

Adolescent↗
PubMed1999

Intermediate filament interactions can be altered by HSP27 and alphaB-crystallin.

HSP27 and alphaB-crystallin are both members of the small heat shock protein family. alphaB-crystalllin has been proposed to modulate intermediate filaments and recently a mutation in alphaB-crystallin has been identified as the genetic basis of desmin related myopathy. This disease is characterised in its pathology by aggregates of intermediate filaments associated with alphaB-crystallin. Here we report that HSP27 like alphaB-crystallin is associated with glial fibrillary acidic protein and vimentin intermediate filament networks in unstressed U373MG astrocytoma cells. HSP27 is also associated with keratin filaments in MCF7 cells, indicating that this association is not restricted to a particular intermediate filament type. The association of sHSPs with both the soluble and filamentous intermediate filament fractions of U373 cells was demonstrated biochemically. Heat shock or drug treatments induced a co-collapse of intermediate filaments and associated small heat shock proteins. These data show that the presence of HSP27 or alphaB-crystallin could not prevent filament collapse and suggest that the purpose of this association is more than just filament binding. Indeed, in U373MG cells the intermediate filament association with small heat shock proteins is similar to that observed for another protein chaperone, HSC70. In order to discern the effect of different chaperone classes on intermediate filament network formation and maintenance, several in vitro assays were assessed. Of these, falling ball viscometry revealed a specific activity of small heat shock proteins compared to HSC70 that was apparently inactive in this assay. Intermediate filaments form a gel in the absence of small heat shock proteins. In contrast, inclusion of alphaB-crystallin or HSP27 prevented gel formation but not filament assembly. The transient transfection of GFAP into MCF7 cells was used to show that the induction of a completely separate network of intermediate filaments resulted in the specific association of the endogenous HSP27 with these new GFAP filaments. These data lead us to propose that one of the major functions of the association of small heat shock proteins with intermediate filaments is to help manage the interactions that occur between filaments in their cellular networks. This is achieved by protecting filaments against those non-covalent interactions that result when they come into very close proximity as seen from the viscosity experiments and which have the potential to induce intermediate filament aggregation as seen in some disease pathologies.

Cell Compartmentation↗
PubMed1999

Nuclear organisation of NIPP1, a regulatory subunit of protein phosphatase 1 that associates with pre-mRNA splicing factors.

Protein phosphatase-1 (PP1) is complexed to many proteins that target it to particular subcellular locations and regulate its activity. Here, we show that 'nuclear inhibitor of PP1' (NIPP1), a major nuclear PP1-binding protein, shows a speckled nucleoplasmic distribution where it is colocalised with pre-mRNA splicing factors. One of these factors (Sm) is also shown to be complexed to NIPP1 in nuclear extracts. Immunodepletion of NIPP1 from nuclear extracts, or addition of a 'dominant negative' mutant lacking a functional PP1 binding site, greatly reduces pre-mRNA splicing activity in vitro. These findings implicate the NIPP1-PP1 complex in the control of pre-mRNA splicing.

Carrier Proteins↗
PubMed1998

Three murine cataract mutants (Cat2) are defective in different gamma-crystallin genes.

A number of murine cataract mutations have been localized to chromosome 1 close to the gamma-crystallin gene cluster (Cryg) (Everett et al., 1994, Genomics 20: 429-434; Löster et al., 1994, Genomics 23: 240-242). Based on the size of the mapping or allelism tests they have not been shown to be genetically distinct and have been assigned to locus symbol Cat2. Here we assign three mutations to the respective gamma-crystallin gene. Using a systematic candidate gene approach to analyze the entire Cryg cluster, an A-->G transition was found in exon 2 of Cryga for the ENU-436 mutation and is designated Cryga1Neu. The mutant allele Crygbnop (formerly Cat2(nop)) is caused by a replacement of 11 bp by 4 bp in the third exon of Crygb, while a C-->G transversion in exon 3 of Cryge has been found for the Cryget (formerly Cat2(t)) mutation. For the mutation Cryga1Neu, an Asp-->Gly exchange is deduced, whereas the mutations Crygbnop and Cryget lead to the formation of in-frame stop codons and give rise to truncated proteins of 144 and 143 amino acids, respectively. The effects of the mutations upon gamma-crystallin structure are likely to be quite different. The Cryga1Neu mutation is expected to affect the link between Greek-key motifs 2 and 3, whereas both Crygbnop and Cryget mutations are supposed to truncate the fourth Greek-key motif. All three mutations are predicted to alter protein folding of the gamma-crystallins and result in lens cataract, but the phenotype for each is quite distinctive.

Amino Acid Sequence↗
PubMed1998

AMP-activated protein kinase: greater AMP dependence, and preferential nuclear localization, of complexes containing the alpha2 isoform.

Mammalian AMP-activated protein kinase (AMPK) is the downstream component of a cascade that is activated by cellular stresses associated with ATP depletion. AMPK exists as heterotrimeric alphabetagamma complexes, where the catalytic subunit has two isoforms (alpha1 and alpha2) with different tissue distributions. The budding yeast homologue is the SNF1 kinase complex, which is essential for derepression of glucose-repressed genes, and seems to act by the direct phosphorylation of transcription factors in the nucleus. AMPK complexes containing the alpha2 rather than the alpha1 isoform have a greater dependence on AMP (approx. 5-fold stimulation compared with approx. 2-fold) both in direct allosteric activation and in reactivation by the upstream kinase. We have also examined their subcellular localization by using Western blotting of nuclear preparations, and by using two detection methods in the confocal microscope, i.e. indirect immunofluorescence of endogenous proteins and transfection of DNA species encoding green fluorescent protein-alpha-subunit fusions. By all three methods a significant proportion of alpha2, but not alpha1, is localized in the nucleus. Like SNF1, AMPK-alpha2 complexes could therefore be involved in the direct regulation of gene expression. The observed differences in the regulation of alpha1 and alpha2 complexes by AMP might result in differential responses to ATP depletion in distinct cellular and subcellular locations.

AMP-Activated Protein Kinases↗
PubMed1995

Synaptogenesis and distribution of presynaptic axonal varicosities in low density primary cultures of neocortex: an immunocytochemical study utilizing synaptic vesicle-specific antibodies, and an electrophysiological examination utilizing whole cell recording.

Low-density primary cultures of neocortical neurons were utilized to examine: (i) early interactions of growing neurites with morphological characteristics of axons with other neuronal elements, and (ii) the distribution of presynaptic axonal varicosities closely apposed to MAP-2 immunoreactive, putatively postsynaptic, dendrites. At the light microscopical level axonal varicosities, presumably presynaptic terminals, were identified using immunocytochemistry incorporating antibodies specific for the synaptic vesicle antigens synaptophysin and synapsin. The presence of synaptophysin- and synapsin-immunoreactive swellings along axonal processes was first detected at 5 days post-plating and was also apparent in axons growing in isolation. At 5-7 days in vitro, immunolabelled axonal varicosities in close apposition to putative postsynaptic dendrites (MAP-2 immunoreactive) dendrites were detected. Electrophysiologically active synaptic contacts can also readily be detected at this stage. After 3 weeks in vitro presynaptic contacts do appear to be distributed heterogeneously along postsynaptic dendrites of many neurons in culture. As the culture matures a higher number of presynaptic profiles can be seen along dendrites, with a centrifugal distribution, e.g. a higher density of presynaptic axonal terminals in close apposition to more distal regions of larger dendrites, putatively considered to be apical dendrites of pyramidal-like neurons. In our cultures, the overall increase in the density and the pattern of distribution of presynaptic axon terminals immunoreactive for synaptic vesicle antigens closely apposed to putative post-synaptic structures mimics the general postnatal increase of synaptic density in the neocortex in vivo. Thus, low density primary cultures of neocortical neurons offer a valuable system to explore and manipulate (i) the molecular and cellular basis of neocortical synaptogenesis, and (ii) the pharmacology of neocortical synaptic transmission.

Animals↗
PubMed1994

A correlated study of metabolic cell communication and gap junction distribution in the adult frog lens.

By using low molecular weight dye injection and laser scanning confocal microscopy it has been possible to assess the degree of dye communication in several regions (intraepithelial, epithelium-fibre cell, fibre-epithelium and fibre-fibre) of the adult frog lens. These same areas of the lens have also been examined by freeze fracture electron microscopy for the presence and organisation of gap junctions. Epithelial cell lateral membranes have numerous gap junctions which efficiently transmitted dye to their neighbours though none was detectable in the underlying fibre cells. This was correlated with an apparent absence of gap junctions at the epithelium/fibre cell interface. Dye spread between cortical fibre cells was only observed in a subset of fibres in the bow region of the lens. Neither mature cortical fibres nor immature bow fibres appeared to be dye-coupled and we detected no dye passed from fibre cells to adjacent epithelial cells at their anterior ends. This pattern of dye communication was also correlated with the apparent absence of recognisable gap junctions on the lateral membranes of either the recently differentiated bow fibres or the mature cortical fibres. Classical gap junctions were only found on the membranes of fibres between five and ten cells in from the lens bow, i.e. the subset of fibres which were dye-coupled. No gap junctions were found between deeper cortical fibres or nuclear fibres, although they were characterised by a number of square arrays. Though electrically well coupled the adult frog lens may be relatively poorly dye coupled and this could depend on the age and differentiation stage of the cells concerned. The model of a freely communicating lens clearly requires re-examination by correlated physiological and morphological studies.

Animals↗
PubMed1994

Recognition of the major cell surface glycoconjugates of Leishmania parasites by the human serum mannan-binding protein.

Activation of complement on the surface of parasitic protozoa of the genus Leishmania appears to be important for parasite infectivity in the mammalian host, as it allows these parasites to attach to and invade macrophages via their surface complement receptors. Serum mannan-binding protein (MBP) is a known activator of complement. Therefore, in the present study, we have investigated whether serum MBP binds to live Leishmania parasites, and to mannose-containing saccharides derived from the parasite cell surface. We have observed by fluorescence microscopy that biotinylated MBP binds to the surface of L. major and L. mexicana promastigotes. At this developmental stage the parasites are coated by a mannose-containing lipophosphoglycan (LPG). We have observed that radioiodinated MBP binds in a mannose-inhibitable manner to purified LPG which has been immobilized in plastic microwells, as well as to purified mannose-terminating di-, tri- and tetrasaccharide fragments ('cap' structures) which have been released by mild acid hydrolysis from the outer chains of the LPG, converted into neoglycolipids and resolved by thin-layer chromatography. 125I-MBP also binds in the chromatogram-binding assay to the mannose-containing glycoinositol-phospholipids that are expressed in high copy number on both the promastigote and the intracellular amastigote stages of most Leishmania species. These data suggest that MBP has the potential to opsonize the major developmental stages of Leishmania parasites, and provide a possible mechanism for the antibody-independent activation of complement on their surface.

Animals↗
PubMed1993

Cytoskeletal changes associated with cell motility.

This chapter reviews various aspects of changes in cytoskeletal organization which occur upon activating a highly motile cell phenotype. The first of these relates to the rapid formation of F-actin-rich ruffles on the apical cell surfaces following the addition of one of several motility factors. In a number of aspects these ruffles resemble leading edge lamellipodia. The ruffles form upon ligand binding and, at least for one cytokine, the receptors become associated with the ruffles. For several cytokines the ruffles are circular and in all cases they are associated with much increased pinocytosis. The possible significance is considered of these very early markers of a motile cell phenotype. A second topic covered is the role of microtubules (MTs) in maintaining cell polarity in some cell types but not others. The micro-injection of biotin-tubulin into cells has provided a valuable marker of MT turnover. Using this method it has been found that the microtubule network in secondary chick heart fibroblasts (2 degrees CHFs), where MTs are required to maintain a polarized motility, does not turn over significantly more slowly than in 1 degree CHFs which do not require an intact MT network for locomotion. In both cases the MT network turns over very quickly and no sub-population of longer-lived MTs has been found. In contrast, in motile epithelial (PtK2) cells, a sub-population of longer-lived microtubules has been identified and these appear to maintain the long cell processes.

Animals↗
PubMed1992

Progression of nonproliferative diabetic retinopathy and visual outcome after extracapsular cataract extraction and intraocular lens implantation.

Twenty-one patients with symmetric nonproliferative retinopathy who underwent extracapsular cataract extraction and intraocular lens implantation were followed up postoperatively for an average (+/- standard deviation) of 18 +/- 7 months to determine the incidence of progression of diabetic retinopathy, the final visual acuity, and factors predictive of progression of retinopathy and final visual acuity. Progression of retinopathy, defined as the development of clinically significant macular edema, an increase in intraretinal hemorrhages or hard exudate, or the development of proliferative diabetic retinopathy, was assessed in both eyes of 19 patients; in two remaining patients, dense preoperative cataract in the fellow eye precluded comparison of retinopathy progression in the operated-on eye to progression in the fellow eye. Overall, retinopathy progressed in 14 of 19 operated-on eyes (74%). Cataract extraction was highly associated with asymmetric progression of nonproliferative retinopathy; it progressed only in the operated-on eye in seven of 19 patients (37%), but in no patients did progression occur in the fellow eye alone (P = .0078). Women had a significantly increased risk of progression of retinopathy in the operated-on eye compared to men (P = .005). Visual acuity improved in 19 of 21 operated-on eyes (86%); however, only 11 eyes (52%) achieved a visual acuity of 20/50 or better and only six eyes (14%) achieved a visual acuity of 20/25 or better. In only five eyes was the final visual acuity in the operated-on eye more than two lines better than the final visual acuity in the fellow eye.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Spontaneous pneumomediastinum: clinical and natural history.

STUDY OBJECTIVE: To evaluate the clinical characteristics and natural history of patients presenting with spontaneous pneumomediastinum. DESIGN: A retrospective case series was conducted to identify patients diagnosed with spontaneous pneumomediastinum. ICD-9 discharge codes were used for 1984 to 1990 at two institutions, and emergency department records of a third hospital were reviewed for 1981 to 1986. Clinical features, interventions, complications, setting, etiology, symptoms, and length of hospital stay were recorded. SETTING: Three university tertiary care hospitals. PARTICIPANTS: All ED patients more than 12 years old with a diagnosis of spontaneous pneumomediastinum. INTERVENTIONS: None. RESULTS: Seventeen cases were identified. Age range was 15 to 41 years (mean, 25 years). Presenting symptoms were chest pain in eight (47%), dyspnea in three (18%), both symptoms in three (18%), and neither in three (18%). Three patients complained only of throat discomfort. Nine (52%) had a Hamman's crunch, 11 (65%) had subcutaneous emphysema, and two (11%) had a small pneumothorax. Five (29%) were smokers, and five (29%) had normal esophograms. Thirteen of 17 (76%) cases were associated with illicit inhalation drug use. Twelve cases (70%) had history of a "Valsalva-type" maneuver. All but three were admitted to a hospital, with a mean stay of 2.5 days (range, one to six). No patient suffered complications or required interventions for spontaneous pneumomediastinum. Specifically, no patient developed a subsequent pneumothorax or airway compromise. The three patients not admitted were followed up by telephone contact. All did well with rapid resolution of their symptoms. CONCLUSION: Most spontaneous pneumomediastinum cases occur in the setting of inhalational drug use. One hundred percent of patients will have a symptom directly related to the spontaneous pneumomediastinum, with 82% presenting with either dyspnea or chest pain. Most (88%) will present with either subcutaneous emphysema or a Hamman's crunch on examination. Simple spontaneous pneumomediastinum has a very benign course and does not require hospitalization. Serial radiographs, likewise, did not change the medical management of spontaneous pneumomediastinum.

Administration, Inhalation↗
PubMed1992

Outcome and cost analysis of scheduled versus emergency scleral buckling surgery.

BACKGROUND: Retinal detachments are usually considered to be a surgical emergency. However, there are additional risks and costs for unnecessary emergency surgeries. The purpose of this study is to evaluate whether the conventional wisdom for treating all retinal detachments as emergencies needs to be re-examined. METHODS: Forty-eight patients who had an emergency scleral buckle and 89 patients who had a scheduled procedure were randomly selected from 884 consecutive patients who had a primary scleral buckling procedure during a 4 1/2-year period. The medical records of each patient were used to obtain detailed information related to prognosis. The visual acuity measurements of each patient, taken 6 months after the procedure, were obtained from the records of the ophthalmologist following the patient. Linear regression analysis was used to compare the final visual outcome for patients who had emergency surgery with patients who had scheduled surgery after taking into account patient factors related to prognosis. RESULTS: Patients selected for emergency surgery had better visual prognoses than scheduled patients but had the same risk of systemic complications and the same extent of detachment if the macula was not involved. None of the 18 patients with an attached macula experienced macular involvement while awaiting scheduled surgery. There were no differences between emergency and scheduled patients in ocular or systemic complications, rate of reattachment, rate of decreased visual acuity after surgery, visual outcome adjusted for prognosis, or, since 1985, length of hospital stay. A greater cost was incurred for the patients having emergency surgery due to difference in pay scales for support personnel. CONCLUSIONS: Because the study is not large and the patients were not randomized to treatment, the results are not definitive. However, they suggest that emergency surgery is unnecessary for many patients with a detached retina.

Appointments and Schedules↗