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Biomedical subjects

M Cross

Publications and source records attributed to M Cross.

At least 199 records · Page 11Linked to original sources
PubMed1992

Loco-regional recurrence and survival after wide local excision, radiotherapy and axillary clearance for early breast cancer.

After breast conservation for early breast cancer which comprised wide local excision, axillary clearance and radiotherapy to the breast, 145 women have been followed prospectively for a median of 42 months. Local recurrence occurred in 11 (7%) and axillary recurrence in three (2%). Distant recurrence has occurred in 32 and accounted for 80% of all first recurrences. Local treatment failure has occurred in three women and would not have been prevented by mastectomy. Loco-regional recurrence in the absence of preceding or synchronous distant disease was unusual and did not pose a significant clinical problem.

Adult↗
PubMed1991

Affinity purification of Trypanosoma brucei small nuclear ribonucleoproteins reveals common and specific protein components.

We have developed a procedure for the affinity purification of small nuclear ribonucleoproteins (snRNPs) of Trypanosoma brucei (U2 and U4/U6 snRNPs), which are essential for trans splicing. Each of these snRNPs can be specifically and efficiently selected from T. brucei extracts through biotinylated antisense 2'-O-methylated RNA oligonucleotides immobilized on streptavidin-agarose. Protein analysis revealed a set of five low molecular weight polypeptides common to the U2 and U4/U6 snRNPs and the spliced leader RNP. In addition, several U2 and U4/U6 snRNP-specific protein components were identified. Using monoclonal antibodies against human snRNP proteins, we could not detect any significant cross-reaction with the trypanosomal U2 snRNP proteins. Thus, the trypanosomal snRNPs exhibit principal differences from the higher eukaryotic snRNPs not only in their RNA but also in their protein components.

Animals↗
PubMed1991

Preparation, properties, and plasma retention of human hemoglobin derivatives: comparison of uncrosslinked carboxymethylated hemoglobin with crosslinked tetrameric hemoglobin.

Human hemoglobin A has been crosslinked by diisothiocyanatobenzenesulfonate to give a limited number of products in a yield of approximately 70%. The predominant product was crosslinked between subunits within a tetramer and had a Mr of 64,000; no higher Mr species were formed. This product had one crosslink per tetramer located between the NH2 termini of its alpha chains, as established by HPLC analysis, amino acid analysis, Edman degradation, and mass spectrometry. This crosslinked derivative had a slightly increased oxygen affinity [P50 = 9 mmHg (1 mmHg = 133 Pa); P50 for unmodified hemoglobin = 11 mmHg], and the retention time of this derivative in the circulation of rats was 2.9 and 3.3 hr at two hemoglobin concentrations (7 g/dl and 14 g/dl, respectively). The half-life of an uncrosslinked carboxymethylated derivative, which has a low oxygen affinity (P50 = 28 mmHg), was 0.6 and 0.7 hr under the same conditions. Therefore, prolongation of the plasma-retention time of infused hemoglobin is dependent on the crosslinking of the tetramer but independent of the oxygen affinity of the derivative.

Allosteric Regulation↗
PubMed1991

Growth factors in development, transformation, and tumorigenesis.

Mammalian tissue development and regeneration take place within a milieu of regulatory growth factors. These affect many parameters of cell development, such that survival, proliferation, differentiation, and certain aspects of cell behavior are all influenced by a balance between stimulatory and inhibitory signals. The precise effect of any given factor is determined by the responding cell type, the concentration of factor, and the presence of other stimuli, such that some growth factors may fulfill a variety of functions under different circumstances. Classically, growth factor stimuli are transmitted into the cell via activation of specific, transmembrane receptors that modify key regulatory proteins in the cytoplasm. These in turn affect the decisions controlling proliferation and differentiation, including changes in gene expression and reactivity to other factors. There are indications that some factors may function both extra- and intracellularly and that this characteristic is correlated with potential oncogenicity. The relatively low transforming ability of extracellular factors alone is probably attributable to the limitations imposed by down-regulation of their cell surface receptors. Aberrant production of secreted growth factors can, however, play decisive roles in tumorigenesis by increasing the proliferation rate and degree of cellular autonomy and extending the area available for tumor expansion.

Animals↗
PubMed1991

Independent movement of cusps during occlusal loading.

An integrated experimental and theoretical approach is proposed for the evaluation of stress within a natural tooth during bruxing. A physical model was developed that used strain gauges bonded to the buccal and lingual heights of contour of extracted, intact maxillary premolar teeth for the validation of a two-dimensional finite element model of a natural, intact maxillary premolar tooth. Results from the finite element model were in good agreement with the experimental results. The tooth exhibits "cuspal independence", which describes the relative independence of the loaded cusp from the remaining cusp that is not loaded. In other words, the control cusp does not demonstrate significant strain when the adjacent cusp is loaded. The overall stiffness of the tooth does not appear to be significantly affected by separation of the enamel of the two cusps and appears to be primarily a function of the dentin.

Bicuspid↗
PubMed1991

Analysis of small nuclear ribonucleoproteins (RNPs) in Trypanosoma brucei: structural organization and protein components of the spliced leader RNP.

trans splicing in Trypanosoma brucei involves the ligation of the 40-nucleotide spliced leader (SL) to each of the exons of large, polycistronic pre-mRNAs and requires the function of small nuclear ribonucleoproteins (snRNPs). We have identified and characterized snRNP complexes of SL, U2, U4, and U6 RNAs in T. brucei extracts by a combination of glycerol gradient sedimentation, CsCl density centrifugation, and anti-m3G immunoprecipitation. Both the SL RNP and the U4/U6 snRNP contain salt-stable cores; the U2 snRNP, in contrast to other eucaryotic snRNPs, is not stable under stringent ionic conditions. Two distinct complexes of U6 RNA were found, a U6 snRNP and a U4/U6 snRNP. The structure of the SL RNP was analyzed in detail by oligonucleotide-directed RNase H protection and by in vitro reconstitution. Our results indicate that the 3' half of SL RNA constitutes the core protein-binding domain and that protein components of the SL RNP also bind to the U2 and U4 RNAs. Using antisense RNA affinity chromatography, we identified a set of low-molecular-mass proteins (14.8, 14, 12.5, and 10 kDa) as components of the core SL RNP.

Animals↗
PubMed1991

A new U6 small nuclear ribonucleoprotein-specific protein conserved between cis- and trans-splicing systems.

Spliceosomal U6 small nuclear RNA (snRNA) plays a central role in the pre-mRNA splicing mechanism and is highly conserved throughout evolution. Previously, a sequence element essential for both capping and cytoplasmic-nuclear transport of U6 snRNA was mapped in the 5'-terminal domain of U6 snRNA. We have identified a protein in cytoplasmic extracts of mammalian and Trypanosoma brucei cells that binds specifically to this U6 snRNA element. Competition studies with mutant and heterologous RNAs demonstrated the conserved binding specificity of the mammalian and trypanosomal proteins. The in vitro capping analysis of mutant U6 snRNAs indicated that protein binding is required but not sufficient for capping of U6 snRNA by a gamma-monomethyl phosphate. Through RNA affinity purification of mammalian small nuclear ribonucleoproteins (snRNPs), we detected this protein also in nuclear extract as a new specific component of the U6 snRNP but surprisingly not of the U4/U6 or the U4/U5/U6 multi-snRNP. These results suggest that the U6-specific protein is involved in U6 snRNA maturation and transport and may therefore be functionally related to the Sm proteins of the other spliceosomal snRNPs.

Animals↗
PubMed1991

Ultrastructural studies of the reaction of urate crystals with a cultured renal tubular cell line.

Hypotheses concerning the development of uric acid and gouty nephropathy suggest that the initiating disease mechanism involves an interaction between uric acid or monosodium urate monohydrate (MSUM) crystals and renal tubular epithelial cells. We have studied the interaction of these crystals with Madin-Darby canine kidney (MDCK) cells, which exhibit many of the characteristics of cells of the collecting duct epithelium. Addition of MSUM crystals to monolayer cultures of MDCK cells leads to the formation of reaction sites, localised areas which are raised above the monolayer forming a 3-dimensional structure. These reaction sites are evident within 4-8 h and appear to be initiated by the interaction of a single crystal or small number of crystals with a single cell. With time, both cells and crystals accumulate at the site. By 24 h most reaction sites involve 6-12 cells and numerous crystals. Interaction of MSUM crystals and MDCK cells not only involves the attachment of crystals to cells but, by 8 h, some crystals appear to be completely or partially covered by the cell membrane, and MDCK cells appear to react by growing around the crystals. Transmission electron microscopy shows that crystals are found not only within cells, but also within the intercellular spaces. Within the cells, crystals have been shown in vacuoles containing lysosomal enzymes, indicating the formation of a phagolysosome. Ultimately, enzyme release occurs. These studies support the hypothesis that some interstitial deposits of urate and uric acid in the kidney may be derived from intratubular deposits that react with the tubular epithelium and pass into the interstitium; loss of tubular integrity may not be a prerequisite for crystal migration.

Animals↗
PubMed1990

A controlled evaluation of an allopurinol mouthwash as prophylaxis against 5-fluorouracil-induced stomatitis.

Pursuant to a promising report suggesting that an allopurinol mouthwash could have a protective effect against 5-fluorouracil (5-FU)-induced stomatitis, the authors performed a randomized, placebo-controlled, double-blind, crossover study. Seventy-seven patients, receiving their first 5-day course of chemotherapy with 5-FU +/- leucovorin, were assigned to use a mouthwash containing 20 mg of allopurinol or a placebo. The mouthwash was administered every hour for four doses commencing with each chemotherapy dose. The severity of subsequent mucositis was graded (on a 0-4 scale) by the attending physician and also by a patient-completed questionnaire. There was trend toward less mucositis in the placebo group with mean physician-judged mucositis scores of 1.3 for placebo and 1.8 for allopurinol (P = 0.07) and mean patient-judged mucositis scores of 1.5 for placebo and 1.9 for allopurinol (P = 0.15). There were no substantial differences in mucositis attributable to the two mouthwashes in the patients who crossed-over on their second cycle of chemotherapy. These data demonstrate that the tested allopurinol mouthwash regimen does not offer any protective effect against 5-FU-induced mucositis.

Allopurinol↗
PubMed1990

Repetitive sequence involvement in the duplication and divergence of mouse lysozyme genes.

Mouse M and P lysozymes are the products of separate genes, are specifically expressed in separate tissues, and are adapted to different functions. The lysozyme genes have assumed these markedly different characteristics following their generation by gene duplication 30-50 million years ago. The discovery of the lysozyme P gene only 5 kb upstream from the M gene in tandem repeat has enabled an investigation of the molecular basis of their duplication and subsequent divergence. The duplication is shown to have involved recombination between two B2 repeat sequences flanking the original gene. The resulting downstream copy has retained the myeloid specificity of expression along with just 1.7 kb of upstream sequences, while the upstream copy is inactive in macrophages and has become expressed instead in the small intestine. Although multiple gene conversion events have served to maintain a generally high homology between the genes, certain regions have been found to be specific for either one of the gene pair: two repetitive sequences peculiar to the P region may serve to protect the coding regions from gene conversion, while sequences unique to the M gene may be more directly involved in differential regulation.

Amino Acid Sequence↗
PubMed1990

Reaction of MDCK cells to crystals of monosodium urate monohydrate and uric acid.

Madin-Darby canine kidney (MDCK) cells exhibit many of the characteristics of cells of the cortical collecting tubule. Since hypotheses concerning the development of gouty and uric acid nephropathy involve a reaction between such cells and crystals, either of monosodium urate monohydrate (MSUM) or uric acid, the reaction between MDCK cells in culture and the above crystals was studied, both morphologically and functionally. In monolayer cultures, reaction sites developed within four hours of exposure to urate crystals. These increased in number for up to 72 hours and subsided gradually after removal of the crystals. At these reaction sites, crystals were observed to have passed beneath the cell surface and could be demonstrated both within intra-cellular lysosomes as well as within the inter-cellular spaces. When the MDCK cells were maintained as single cells in suspension, phagocytosis of crystals by the majority of the cells could be observed, but the response was much more rapid than in monolayers. During the cell/crystal reaction, significant amounts of lysosomal enzymes and prostaglandin E2 were released and, to a less significant degree, cytosolic enzymes, presumably due to cell lysis. This enzyme release did not occur in MDCK cells grown in protein-free medium, and protein coating of the crystals was necessary for reactivity with cells. In this regard, coating with IgG or lysozyme was more effective than albumin. The reaction with uric acid crystals revealed a reactivity which was lesser in degree but qualitatively similar to that of urate crystals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Isolation of the Actinobacillus pleuropneumoniae haemolysin gene and the activation and secretion of the prohaemolysin by the HlyC, HlyB and HlyD proteins of Escherichia coli.

The gene encoding the c. 105 kD secreted haemolysin protein of the porcine pathogen Actinobacillus pleuropneumoniae serotype 1 has been isolated by screening a lambda gt11 expression library in Escherichia coli with antiserum raised against the wild-type protein. A derivative recombinant DNA pJFF702 expressed the hlylA haemolysin gene from the pUC19 lac promoter but the resulting haemolysin I protein remained within the E. coli cell and was haemolytically inactive. Export of the intracellular A. pleuropneumoniae prohaemolysin out into the medium was achieved by the presence in trans of the E. coli haemolysin secretion genes hlyB and hlyD, and high levels of intracellular haemolytic activity were attained similarly by the E. coli post-translational haemolysin activator gene, hlyC. Southern hybridization of A. pleuropneumoniae parental DNA nevertheless indicated only a low degree of nucleotide sequence identity to the haemolysin structural and secretion genes hlyA and hlyB of E. coli. The data show that despite substantial nucleotide sequence divergence the A. pleuropneumoniae serotype 1 haemolysin determinant is closely related to that which is dispersed throughout other Gram-negative human and animal pathogens.

Actinobacillus↗
PubMed1989

The cytotoxic effects of estradiol-17 beta, catecholestradiols and methoxyestradiols on dividing MCF-7 and HeLa cells.

In this study the cytotoxic effects of high concentrations (greater than or equal to 1 x 10(-6) M) of estradiol-17 beta (E2), 2-/4-hydroxyestradiol-17 beta (2-/4-OHE2) and 2-/3-/4-methoxyestradiol-17 beta (2-/3-/4-MeOE2) were determined on dividing MCF-7 and HeLa cells. The 2-MeOE2 metabolite followed by 2-OHE2 and E2 (in this order) proved to be extremely toxic to dividing MCF-7 and HeLa cells. The cytotoxic effect on these cells comprised uneven chromosome distribution. Indirect immunofluorescent studies, in which monoclonal anti-alpha-tubulin antibodies were used, showed that these compounds (2-MeOE2 greater than 2-OHE2 greater than E2) at high concentrations caused abnormal and fragmented polar formations as well as disorientated microtubule arrangement in the dividing MCF-7 and HeLa cells. The 4-OHE2 and 3-/4-MeOE2 metabolites had little or no cytotoxic effects on dividing cells. The large number of abnormal metaphases seen in HeLa cells exposed to 2-MeOE2 suggested that this metabolite may be the ultimate cytotoxic compound. The reduction in the number of HeLa cells with abnormal metaphase configurations after exposure to 2-OHE2 plus quinalizarin (an inhibitor of catechol-O-methyltransferase) indicated that the production of 2-MeOE2 is necessary for the formation of abnormal spindles in metaphase. Quinalizarin treatment in the presence of 2-MeOE2 had no effect on the large number of abnormal metaphases. We therefore conclude that neither E2 nor 2-OHE2, but a high concentration of 2-MeOE2 is responsible for abnormal spindle formation. In additional experiments the number of normal and abnormal dividing HeLa cells were greatly reduced when simultaneously exposed to E2 and 2-/4-hydroxylase-inhibitor alpha-naphthoflavone.

Benzoflavones↗
PubMed1989

Transcription antitermination in an Escherichia coli haemolysin operon is directed progressively by cis-acting DNA sequences upstream of the promoter region.

Export of haemolysin protein (HlyA) directed by the Escherichia coli pHly152 hly determinant is dependent upon transcriptional activation, primarily strong intraoperon transcript antitermination imposed between the haemolysin structural genes hlyC and hlyA and the contiguous downstream export genes hlyB and hlyD. Transcript elongation was dictated by a DNA sequence several kb upstream of the rho-independent terminator but could not be assigned to a discrete locus; on the contrary, it was progressive, increasing with the addition of up to 3.5 kbp of operon-proximal sequence containing the insertion elements IS2 and IS91. Antitermination was prominent throughout logarithmic growth but absent in stationary phase, and was effective only in cis but not in trans. Primer extension indicated that transcription activation utilized the native transcriptional start sites of the unactivated hly operon.

Base Sequence↗
PubMed1989

EMS communications: an inside look at New York City.

The opportunity to provide effective EMS begins at the point of citizen access, with successive links to emergency response and medical control. This responsibility places much pressure on the communications division of any EMS system. Communications specialists must be acutely aware that each flashing number on the computer screen represents someone in trouble--a person's life. This unique situation is highlighted when, through emergency medical instructions given over the phone to the caller, a life is saved. This type of event has become more common throughout the United States, with most EMS systems implementing proactive protocols for pre-arrival instructions. The strength of an EMS system directly correlates with the effectiveness of its communications center and the professionalism of communications personnel. Unlike other individuals in the EMS system, communications specialists rarely see their patients "in the flesh" and must experience the rewards of accomplishment vicariously through the actions of the crews dispatched. In the same vein, they also share the tragedies and disappointments that are all too often part of an EMS career.

Allied Health Personnel↗