Biomedical subjects

A M Page

Publications and source records attributed to A M Page.

15 recordsLinked to original sources

PubMed2000

Ultrastructural analysis of Phytomonas species from Euphorbia pinea reveals trans-cytoplasmic filaments 10 nm in diameter.

Phytomonas sp. derived from Euphorbia pinea are digenetic plant trypanosomes that are transmitted by the squashbug Stenocephalus agilis and exist exclusively as promastigotes. The stable sub-pellicular microtubular array, the flagellar axoneme and the paraflagellar rod represent the major cytoskeletal components common to all trypanosomes. The work described in this paper examines in detail the ultrastructural morphology of the organism and highlights a number of novel structural features, and in particular, the presence of some detergent-resistant proteins which take the form of bundles of trans-cytoplasmic filaments of ca. 10 nm in diameter, seen in cells from both log- and stationary-phase cultures. The ultrastructural morphology and immunological cross-reactivity of these filaments are described, and their relationship to filamentous bundles previously reported in stationary-phase cultures of Crithidia fasciculata and to intermediate filaments of animal cells is discussed.

Animals↗

PubMed2000

Plants rendered herbicide-susceptible by cauliflower mosaic virus-elicited suppression of a 35S promoter-regulated transgene.

Crop plants genetically modified for herbicide tolerance were some of the first to be released into the environment. Frequently, the cauliflower mosaic virus (CaMV) 35S promoter is used to drive expression of the herbicide tolerance transgene. We analyzed the response to CaMV infection of a transgenic oilseed rape line containing the bialaphos tolerance gene (BAR) from Streptomyces hygroscopicus, regulated by the 35S promoter. Oilseed rape is susceptible to CaMV, but plants recover from infection. CaMV infection altered the expression of the herbicide tolerance gene such that plants became susceptible to the herbicide. The effect on transgene expression differed in infections with viral pathogenic variants typical of those found in natural situations worldwide. Susceptibility to the herbicide was most likely a result of transcriptional gene silencing of the transgene. Our results show that transgene phenotypes can be modified by pathogen invasion.

Brassica↗

PubMed2000

The APC11 RING-H2 finger mediates E2-dependent ubiquitination.

Polyubiquitination marks proteins for degradation by the 26S proteasome and is carried out by a cascade of enzymes that includes ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), and ubiquitin ligases (E3s). The anaphase-promoting complex or cyclosome (APC/C) comprises a multisubunit ubiquitin ligase that mediates mitotic progression. Here, we provide evidence that the Saccharomyces cerevisiae RING-H2 finger protein Apc11 defines the minimal ubiquitin ligase activity of the APC. We found that the integrity of the Apc11p RING-H2 finger was essential for budding yeast cell viability, Using purified, recombinant proteins we showed that Apc11p interacted directly with the Ubc4 ubiquitin conjugating enzyme (E2). Furthermore, purified Apc11p was capable of mediating E1- and E2-dependent ubiquitination of protein substrates, including Clb2p, in vitro. The ability of Apc11p to act as an E3 was dependent on the integrity of the RING-H2 finger, but did not require the presence of the cullin-like APC subunit Apc2p. We suggest that Apc11p is responsible for recruiting E2s to the APC and for mediating the subsequent transfer of ubiquitin to APC substrates in vivo.

Amino Acid Sequence↗

PubMed1999

The anaphase-promoting complex: new subunits and regulators.

Ubiquitin-mediated proteolysis of cell cycle regulators is a crucial process during the cell cycle. The anaphase-promoting complex (APC) is a large, multiprotein complex whose E3-ubiquitin ligase activity is required for the ubiquitination of mitotic cyclins and other regulatory proteins that are targeted for destruction during cell division. The recent identification of new APC subunits and regulatory proteins has begun to reveal some of the intricate mechanisms that govern APC regulation. One mechanism is the use of specificity factors to impose temporal control over substrate degradation. A second mechanism is the APC-mediated proteolysis of specific APC regulators. Finally, components of both the APC and the SCF E3 ubiquitin-ligase complex contain several conserved sequence motifs, including WD-40 repeats and cullin homology domains, which suggest that both complexes may use a similar mechanism for substrate ubiquitination.

Anaphase↗

PubMed1999

Dystrophic phenotype induced in vitro by antibody blockade of muscle alpha-dystroglycan-laminin interaction.

alpha-dystroglycan is a glycoprotein expressed on the surface of skeletal muscle fibres and other cell types. In muscle, alpha-dystroglycan provides a link between the myofibre cytoskeleton through its indirect binding to dystrophin, and the basal lamina through its binding to laminin-2, a protein of the extracellular matrix. The disruption of this linkage between the myofibre cytoskeleton and the extracellular matrix is a common feature of Duchenne and other muscular dystrophies, though the pathogenic mechanisms leading to muscle wasting remain unknown. By treating primary mouse muscle cultures with a monoclonal antibody which blocks alpha-dystroglycan binding to laminin, we show here the induction of a dystrophic phenotype in vitro. The phenotype is inducible in differentiated cultures only, is characterised by reduced myotube size, myofibril disorganisation, loss of contractile activity, reduced spontaneous clustering of acetylcholine receptors and is reversed by addition of excess exogenous laminin-2. Thus, alpha-dystroglycan may be part of a signalling pathway for the maturation and maintenance of skeletal myofibres. Detailed knowledge of this signalling pathway may provide insights into the molecular pathology of the various inherited muscular dystrophies, and identify valuable pharmacological targets and new therapeutic strategies.

Animals↗

PubMed1998

Mutational analysis of exoribonuclease I from Saccharomyces cerevisiae.

Exoribonuclease I from yeast is a 175 kDa protein that is responsible for the majority of cytoplasmic mRNA degradation. Alignment of the Xrn1p sequence with homologs from yeast as well as from higher eukaryotes suggests that the protein is composed of several domains: two acidic N-terminal domains which likely contain the exonuclease, a basic middle domainand a basic C-terminal domain. Deletion analysisdemonstrated that the C-terminus is dispensable for most in vivo and in vitro functions but confers a dominant negative growth inhibition when expressed at high levels. This growth inhibition is not due to the exonuclease function of the protein. To identify specific residues responsible for in vivo function, a screen was carried out for non-complementing missense mutations. Fourteen single point mutations were identified that altered highly conserved amino acids within the first N-terminal domain of Xrn1p. All of the mutations reduced exonuclease activity measured in vivo and in vitro using affinity-purified proteins. The mutants fell into two phenotypic classes, those that reduced or abolished exonuclease activity without qualitatively changing the products of RNA degradation and those that gave rise to novel degradation intermediates on certain RNAs.

Amino Acid Sequence↗

PubMed1998

Identification of a cullin homology region in a subunit of the anaphase-promoting complex.

The anaphase-promoting complex is composed of eight protein subunits, including BimE (APC1), CDC27 (APC3), CDC16 (APC6), and CDC23 (APC8). The remaining four human APC subunits, APC2, APC4, APC5, and APC7, as well as human CDC23, were cloned. APC7 contains multiple copies of the tetratrico peptide repeat, similar to CDC16, CDC23, and CDC27. Whereas APC4 and APC5 share no similarity to proteins of known function, APC2 contains a region that is similar to a sequence in cullins, a family of proteins implicated in the ubiquitination of G1 phase cyclins and cyclin-dependent kinase inhibitors. The APC2 gene is essential in Saccharomyces cerevisiae, and apc2 mutants arrest at metaphase and are defective in the degradation of Pds1p. APC2 and cullins may be distantly related members of a ubiquitin ligase family that targets cell cycle regulators for degradation.

Amino Acid Sequence↗

PubMed1998

Plastid ontogeny during petal development in Arabidopsis.

Imaging of chlorophyll autofluorescence by confocal microscopy in intact whole petals of Arabidopsis thaliana has been used to analyze chloroplast development and redifferentiation during petal development. Young petals dissected from unopened buds contained green chloroplasts throughout their structure, but as the upper part of the petal lamina developed and expanded, plastids lost their chlorophyll and redifferentiated into leukoplasts, resulting in a white petal blade. Normal green chloroplasts remained in the stalk of the mature petal. In epidermal cells the chloroplasts were normal and green, in stark contrast with leaf epidermal cell plastids. In addition, the majority of these chloroplasts had dumbbell shapes, typical of dividing chloroplasts, and we suggest that the rapid expansion of petal epidermal cells may be a trigger for the initiation of chloroplast division. In petals of the Arabidopsis plastid division mutant arc6, the conversion of chloroplasts into leukoplasts was unaffected in spite of the greatly enlarged size and reduced number of arc6 chloroplasts in cells in the petal base, resulting in few enlarged leukoplasts in cells from the white lamina of arc6 petals.

Arabidopsis↗

PubMed1998

New Arabidopsis cue mutants suggest a close connection between plastid- and phytochrome regulation of nuclear gene expression.

We searched for new components that are involved in the positive regulation of nuclear gene expression by light by extending a screen for Arabidopsis cue (chlorophyll a/b-binding [CAB] protein-underexpressed) mutants (H.-M. Li, K. Culligan, R.A. Dixon, J. Chory [1995] Plant Cell 7: 1599-1610). cue mutants display reduced expression of the CAB3 gene, which encodes light-harvesting chlorophyll protein, the main chloroplast antenna. The new mutants can be divided into (a) phytochrome-deficient mutants (hy1 and phyB), (b) virescent or delayed-greening mutants (cue3, cue6, and cue8), and (c) uniformly pale mutants (cue4 and cue9). For each of the mutants, the reduction in CAB expression correlates with the visible phenotype, defective chloroplast development, and reduced abundance of the light-harvesting chlorophyll protein. Levels of protochlorophyllide oxidoreductase (POR) were reduced to varying degrees in etiolated mutant seedlings. In the dark, whereas the virescent mutants displayed reduced CAB expression and the lowest levels of POR protein, the other mutants expressed CAB and accumulated POR at near wild-type levels. All of the mutants, with the exception of cue6, were compromised in their ability to derepress CAB expression in response to phytochrome activation. Based on these results, we propose that the previously postulated plastid-derived signal is closely involved in the pathway through which phytochrome regulates the expression of nuclear genes encoding plastid proteins.

Arabidopsis↗

PubMed1997

Dietary whole cottonseed depresses lipogenesis but has no effect on stearoyl coenzyme desaturase activity in bovine subcutaneous adipose tissue.

The primary objective of this study was to determine the effect of long-term feeding of whole cottonseed (WCS) on lipogenesis and stearoyl-coenzyme A desaturase activity in growing steers. Brangus steers were fed either a control, cornbased diet (n = 11) or 30% WCS (n = 12). The 30% WCS contributed an estimated 6.6% additional lipid to the diet. Steers fed the added WCS had greater live weights (P = 0.04) and kidney, pelvic, and heart fat (P = 0.005). Subcutaneous fat thickness was not different (P = 0.20) between treatment groups, although WCS elicited an increase in the proportion of large diameter subcutaneous adipocytes. The rate of [U-14C]acetate incorporation into fatty acids in subcutaneous adipose tissue was reduced by dietary WCS (171.4 vs 122.1 nmol x 100 mg adipose tissue-1 x 2 hr-1, P = 0.03), indicating that the increased dietary fat depressed de novo lipogenesis. Hepatic desaturase activity was much lower than that of subcutaneous adipose tissue, a feature common to cattle. We anticipated that added WCS also would depress stearoyl-coenzyme A desaturase activity in subcutaneous adipose tissue and liver due to its cyclopropene fatty acid content. Instead, desaturase activity was numerically (although not significantly) greater in liver (P = 0.37) and adipose tissue (P = 0.23).

Adipose Tissue↗

PubMed1997

The anaphase promoting complex.

We have proposed a preliminary model of how the anaphase promoting complex functions throughout the cell cycle, but despite the flurry of recent publications characterizing the APC--its components, regulation and substrate specificity--many fundamental questions remain to be answered. Firstly, the remaining components of the APC need to be identified and characterized. We do not know if all cyclosome components are conserved in all eukaryotes, or if higher eukaryotes, having a more complicated cell cycle machinery, maintain additional subunits for more sophisticated functional and regulatory control. In addition, we need to determine the identity of the various kinases and phosphatases that regulate the APC itself. The biochemistry of individual APC components is also a mystery, and a specific biochemical function has not been assigned to any known members of the complex. It is not at all clear which subunit(s) of the complex actually recognizes the E2 enzyme and which subunit(s) recognizes the cyclin destruction box. It is likely that many cyclosome substrates remain to be identified, and it will be interesting to determine whether all cyclosome substrates require a destruction box for their degradation or whether the APC recognizes other determinants of protein instability. Finally, we assume that the APC degrades mitotic cyclins in all proliferating cells, but whether it degrades unique cell cycle related substrates in specific tissues is unclear. Furthermore, nothing is known about APC function during meiosis, or whether the APC degrades other substrates that are not related to the cell cycle. This is an exciting and rapidly developing field in the exciting world of cell cycle biology. We expect that new findings will surely reveal many interesting surprises about this essential protein complex.

Anaphase↗

PubMed1996

Exploiting the complete yeast genome sequence.

The completion of the genome sequence of the budding yeast Saccharomyces cerevisiae marks the dawn of an exciting new era in eukaryotic biology that will bring with it a new understanding of yeast, other model organisms, and human beings. This body of sequence data benefits yeast researchers by obviating the need for piecemeal sequencing of genes, and allows researchers working with other organisms to tap into experimental advantages inherent in the yeast system and learn from functionally characterized yeast gene products which are their proteins of interest. In addition, the yeast post-genome sequence era is serving as a testing ground for powerful new technologies, and proven experimental approaches are being applied for the first time in a comprehensive fashion on a complete eukaryotic gene repertoire.

Animals↗

PubMed1995

Effects of phenothiazine neuroleptic drugs on the microtubular-membrane complex in bloodstream forms of Trypanosoma brucei.

African trypanosomes are parasitic protozoa causing sleeping sickness in humans and related diseases in domestic animals against which no entirely satisfactory forms of chemotherapy are yet available. It was previously shown that related species of trypanosomes, as well as procyclic (insect) forms of Trypanosoma brucei are extremely sensitive to the action of phenothiazine neuroleptic drugs in vitro. In this work, we have carried out a more detailed investigation of the effects of thioridazine, one of the most potent neuroleptic phenothiazine drugs known, on the morphology of the infective bloodstream forms of T. brucei, with particular reference to the parasite's prominent pellicular membrane complex. Our data show that this drug induces rapid changes in cell shape that appear to involve some reorganization of the microtubular membrane skeleton, but does not affect the structural integrity of the microtubular complex. Another early consequence of drug action involved damage to nuclear and cytoplasmic membranes and the appearance of tubular arrays of coated membrane within the flagellar pocket. It was also revealed that the drug induces a rapid release of the variant-specific glycoprotein (VSG) which makes up the surface coat protecting bloodstream forms of the parasite against the host immune system. Our evidence suggests that this release of VSG involves cleavage of the protein's glycosyl-phosphatidylinositol (GPI) membrane anchor by endogenous GPI-specific phospholipase C, probably as a consequence of minor damage to the parasite plasma membrane induced by the drug.

Animals↗

PubMed1995

Mucous and serous secretions of human bronchial epithelial cells in secondary culture.

Human bronchial surface epithelial cells were maintained in secondary culture on a collagen gel substrate in a defined, serum-free medium. These conditions have previously been reported to promote mucous cell differentiation. After 3 wk in culture, approximately 40% of the cells were stained by an antibody directed against human respiratory mucin. Analysis of media from cells cultured in the presence of the radioactive precursors [3H]glucosamine and [35S]sulfate revealed that the cells secreted high molecular weight glycoproteins with properties of typical respiratory mucins. In addition, hyaluronic acid and proteoglycans containing chondroitin sulfate and/or heparan sulfate glycosaminoglycans were identified in cell conditioned media. Finally, Western blot analyses showed that the cells secreted lysozyme and mucous proteinase inhibitor, proteins that are generally considered to be markers for submucosal gland serous cells. These results show that human bronchial cells from the surface epithelium in secondary culture secreted a range of glycoconjugates and proteins that were typical secretory products of both mucous and serous cells.

Bronchi↗

PubMed1989

Absence of outer caudal setae on all larval instars of Phlebotomus tobbi from the Ionian Greek islands.

Larval instars 2, 3 and 4 of Phlebotomus tobbi Adler, Theodor & Lourie from the Greek islands of Corfu and Zakynthos were found to have two caudal setae instead of the four usually present on these instars of Phlebotomus larvae. In a scanning electron microscope comparison with larvae of P. papatasi (Scopoli), a sensillum was seen in place of each outer seta of P. tobbi larvae, suggesting secondary loss of the setae. As the larvae of less than a tenth of the species and subspecies of the genus Phlebotomus have been seen and described, it cannot be assumed that those of P. tobbi are unique in having only two caudal setae. However, four caudal setae in late instars can no longer be considered as a constant character of the genus Phlebotomus. Observations on the larvae of P. tobbi also raise the question of the unknown function of the caudal setae.

Animals↗