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D White

Publications and source records attributed to D White.

At least 127 records · Page 7Linked to original sources
PubMed1996

Inhibition of flagellar beat frequency by a new anti-beta-tubulin antibody.

A panel of monoclonal antibodies (mAbs) has been generated against sea urchin sperm axonemes and selected for their ability to inhibit the motility of sea urchin sperm models. The mAb C9 recognized a 50 kDa protein on blots of sea urchin sperm axonemes. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that C9 recognized isoforms of beta-tubulin. Low concentrations of C9 (0.1-1.0 microgram/ml) blocked the motility of sea urchin sperm models by decreasing the sliding velocity and frequency of flagellar beating to less than 1 Hz and by modifying the shear angle along the axoneme, especially the distal end. Other antitubulin antibodies had little effect on motility at concentrations 100-fold higher than those effective for C9. The effects on motility were not restricted to flagella of sea urchin spermatozoa. Flagellar beating of the dinoflagellate Oxyrrhis marina was completely blocked by C9 in a manner reminiscent of that of sea urchin sperm flagella. The mAb also inhibited the motility of human spermatozoa and Chlamydomonas reinhardtii. Immunofluorescence techniques revealed that C9 stains the whole axoneme of sea urchin spermatozoa and O. marina flagella together with the cortical network of O. marina cell body. C9 is the first antitubulin antibody reported to interfere with flagellar beat frequency. The observation that this antibody arrests the motility of flagella from sea urchin sperm along with that of dinoflagellate, algae, and human sperm flagella suggests that the epitope recognized by C9 is conserved over a long period of evolution and plays an important role in sperm motility.

Animals↗
PubMed1996

Hypersecretion of androgens by polycystic ovaries: the role of genetic factors in the regulation of cytochrome P450c17 alpha.

A single base change has been found in the promoter region of CYP17, the gene encoding P450c17 alpha, which appears to be a significant factor in the expression of hyperandrogenism in PCO but which can be excluded as the primary genetic defect. These findings are consistent with the biochemical data from the studies of patients with PCOS reported above, in which the production of ovarian 17 hydroxyprogesterone and androstenedione were observed to be greatly increased but the generation of progesterone was also exaggerated in PCO theca. Thus, genetic factors may well be involved in the observed dysregulation of 17 hydroxylase/17,20 lyase, but this does not appear to be the whole story. It remains a tenable hypothesis that a single-gene effect is the major cause of PCOS and that a gene involved in the expression of androgen production will be implicated. On the other hand, increased androgen production may be a reflection of an 'upstream' abnormality in the ovary, perhaps involving the fundamental processes of proliferation, differentiation and atresia in ovarian follicles. It is also possible that PCOS is truly polygenic and that CYP17 is one of several genes-including those related to insulin secretion and action-that contribute to the PCOS phenotype. Further candidate genes will need to be investigated using well-characterized, large families, but if several predisposing genes are involved, other approaches may be applicable, for example analysis of shared alleles by affected sibling pairs, which has proved valuable in understanding the genetics of type 1 diabetes (Davies et al, 1994). In conclusion, PCOS--one of the most common endocrinopathies--remains an enigmatic condition but one which may prove to be an important model for understanding the interaction of genetic and environmental factors in the aetiology of endocrine disorders.

Alleles↗
PubMed1996

A membrane cofactor protein transgenic mouse model for the study of discordant xenograft rejection.

BACKGROUND: In recent years, interest has been revived in the possibility of transplanting organs into humans from a phylogenetically disparate species such as the pig (xenotransplantation). Such discordant xenografts, however, are subject to hyperacute rejection (HAR) and activation of host complement plays a major role in this rejection. This problem may be solved through the use of transgenic technology by providing the grafted tissue with molecules that down-regulate the action of host complement. RESULTS: Transgenesis with a yeast artificial chromosome (YAC) was used to produce transgenic mice with the complete genomic gene of the human complement regulator membrane cofactor protein (MCP). Transgenic mice were obtained that exhibit full regulation of MCP as normally observed in humans. Hearts from these mice were shown to be significantly protected from HAR caused by human serum in an in vivo experimental procedure. CONCLUSIONS: We conclude that MCP can protect discordant xenografts from HAR caused by human serum and that transgenic mice can be used effectively as in vivo models for the study of the role of human complement regulatory molecules in xenotransplantation.

Animals↗
PubMed1996

Moderating binge drinking: it is possible to change behaviour if you plan it in advance.

Recent theories of enactment suggest that behaviour change is increased by planning how, where, and when to execute a behavioural response. Drawing on these theories, a brief planning intervention was designed and its effectiveness compared to an information-based health promotion programme (control). All participants were given information about the safe limits per drinking occasion and the adverse consequences of binge drinking, and were asked to drink within the safe limits in order to avoid these consequences. In addition, participants in the planning group received an option menu of possible responses for refusing a drink, asked to choose one strategy and specify a time and place in which the chosen strategy would be implemented. The planning intervention group did not differ from the control group on reported likelihood of future binge drinking, nor on levels of past drinking, age and gender. At a 2-week follow-up, members of the planning intervention group reported lower drinking frequency than controls. The implications of prior planning for interventions aimed at reducing alcohol-related harm are discussed.

Adolescent↗
PubMed1996

The d

Explore the source record for details and available documents.

Journal Article↗
PubMed1996

Gliding motility in slide cultures of Myxococcus xanthus in stable and steep chemical gradients.

A method was devised to construct stable and steep chemical gradients in slide cultures to study the movements of gliding cells. The movement of Myxococcus xanthus individual cells and small swarms was studied in these gradients. There was no response to gradients of Casitone and yeast extract that were previously reported to stimulate a positive chemotactic response with M. xanthus.

Caseins↗
PubMed1996

The polyglutamylated lateral chain of alpha-tubulin plays a key role in flagellar motility.

To investigate whether a specific isotype of tubulin is involved in flagellar motility, we have developed and screened a panel of monoclonal antibodies (mAb) generated against sea urchin sperm axonemal proteins. Antibodies were selected for their ability to block the motility of permeabilized sperm models. The antitubulin mAb B3 completely inhibited, at low concentrations, the flagellar motility of permeabilized sperm models from four sea urchin species. On immunoblots, B3 recognized predominantly alpha-tubulin in sea urchin sperm axonemes and equally well brain alpha- and beta-tubulins. Subtilisin cleavage of tubulin removed the B3 epitope, indicating that it was restricted to the last 13 amino acid residues of the C-terminal domain of alpha-tubulin. In enzyme-linked immunosorbant assays, B3 reacted with glutamylated alpha-tubulin peptides from sea urchin or mouse brain but did not bind to the unmodified corresponding peptide, indicating that it recognized polyglutamylated motifs in the C-terminal domain of alpha-tubulin. On the other hand, other tubulin antibodies directed against various epitopes of the C-terminal domain, with the exception of the antipolyglutamylated mAb GT335, had no effect on motility while having binding properties similar to that of B3. B3 and GT335 acted by decreasing the beating amplitude without affecting the flagellar beat frequency. B3 and GT335 were also capable of inhibiting the motility of flagella of Oxyrrhis marina, a 400,000,000 year old species of dinoflagellate, and those of human sperm models. Localization of the antigens recognized by B3 and GT335 by immunofluorescence techniques revealed their presence along the whole axoneme of sea urchin spermatozoa and flagella of O. marina, except for the distal tip and the cortical microtubule network of the dinoflagellate. Taken together, the data reported here indicate that the polyglutamylated lateral chain of alpha-tubulin plays a dynamic role in a dynein-based motility process.

Amino Acid Sequence↗
PubMed1996

Scaling basic toxicokinetic parameters from rat to man.

Scaling of the quantified dispositional parameters of xenobiotics from animals to man is of interest from the standpoint of toxicology (e.g., poisoning and risk assessment). Scaling is also important from the standpoint of therapeutics because it represents a strategy for predicting first-use-in-human doses in clinical trials of investigational new drugs. Current strategies for scaling either doses of xenobiotics or the dispositional parameters of xenobiotics from animals to man rely on models that take account principally of species differences in weight or body surface area. Interspecies scaling of dispositional parameters such as clearance or volume of distribution commonly involves the comparison of estimates of these parameters for a given xenobiotic among numerous species on the basis of weight with the resultant mathematical relationship used to predict the values of those parameters for that xenobiotic in a species weighing, on average, about 70 kg (i.e., a man). Our approach has been to ascertain whether a useful mathematical model could be developed for predicting the dispositional parameters of a xenobiotic, its half-life and volume of distribution, in humans based exclusively on estimates of those parameters in rats. Based on a data set of about 100 different xenobiotics, we found that values for half-life and volume of distribution of a xenobiotic in humans can be predicted from the estimates of those parameters in rats.

Animals↗
PubMed1996

Children's dental health under the capitation scheme.

A study was undertaken of the dental health of 7870 eight-year-old children resident in the City of Birmingham, using the standard British Association of Community Dentistry epidemiological procedures. There were variations in the dental health of children from different ethnic backgrounds. Asian children had the poorest dental health and Afro-Caribbean children, the best. There were also variations in the dental health of children from different ACORN Categories. Children from the highest ACORN Category 'Thriving' had better dental health than those from the lowest, 'Striving' Category. Positive consent was obtained from every parent or guardian to link the findings with the Dental Practice Board's records as to whether each child was registered under the NHS capitation scheme for the provision of primary dental care to children. The dental state of those who were registered in the capitation scheme, (54.5 per cent), was compared with those who were not, (45.5 per cent). The highest proportion of children registered with a dentist were Caucasian and from a high social class i.e. ACORN Category 'Thriving'. In order to ensure that differences were due to their capitation status and not to other differences within the groups, analyses were undertaken according to the ethnic background and ACORN Category of the children. Overall, there were only very small differences between the caries state of the registered and non registered children. However 32 per cent of those children registered in the scheme still had active decay which was not restricted to the primary dentition. The greatest reduction in the average number of decayed teeth together with the greatest increase in the average number of fillings in registered children when compared to their non registered colleagues was observed in the lowest ACORN Category. Unfortunately this group had the lowest proportion of children who were registered in the capitation scheme and 40 per cent of them, both registered and non registered, still had active decay. Overall, oral hygiene was good, and there was little difference between registered and non-registered children in the ACORN Category 'Thriving'. However, in the ACORN Category 'Striving', there was a higher proportion of children with good oral hygiene amongst those who were registered than amongst those who were not. Provision of preventive treatment was low in all registered and non registered groups, but lowest in those groups of children with the poorest dental health. It would appear that, for a proportion of children registered in the capitation scheme, the practitioners were failing to achieve the requirement of "securing and maintaining their oral health".

Africa↗
PubMed1995

Pleckstrin inhibits phosphoinositide hydrolysis initiated by G-protein-coupled and growth factor receptors. A role for pleckstrin's PH domains.

Pleckstrin is a 40-kDa protein present in platelets and leukocytes that contains two PH domains separated by a 150-residue intervening sequence. Pleckstrin is a major substrate for protein kinase C, but its function is unknown. The present studies examine the effects of pleckstrin on second messenger generation. When expressed in cos-1 or HEK-293 cells, pleckstrin inhibited 1) the G alpha-mediated activation of phospholipase C beta initiated by thrombin, M1-muscarinic acetylcholine, and angiotensin II receptors, 2) the stimulation of phospholipase C beta by constitutively active Gq alpha, 3) the G beta gamma-mediated activation of phospholipase C beta caused by alpha 2A-adrenergic receptors, and 4) the tyrosine phosphorylation-mediated activation of phospholipase C gamma caused by Trk A. However, pleckstrin had no effect on either the stimulation or inhibition of adenylyl cyclase. The inhibition of phosphoinositide hydrolysis caused by pleckstrin was similar in magnitude to that caused by activating protein kinase C with phorbol 12-myristate 13-acetate (PMA). When combined, pleckstrin and PMA had an additive effect, inhibiting phosphoinositide hydrolysis by as much as 90%. Structure-function analysis highlighted the role of pleckstrin's N-terminal PH domain in these events. Although deleting the C-terminal PH domain had no effect, deleting the N-terminal PH domain abolished activity (but not expression) and mutating a highly conserved tryptophan residue within the N-terminal PH domain decreased activity by one-third. Notably, however, a pleckstrin variant in which the N-terminal PH domain was replaced with a second copy of the C-terminal PH domain was nearly as active as native pleckstrin. These results show that: 1) pleckstrin can inhibit pathways leading to both phospholipase C beta- and phospholipase C gamma-mediated phosphoinositide hydrolysis, 2) this inhibition affects activation of phospholipase C beta mediated by either G alpha or G beta gamma, but does not affect the regulation of adenylyl cyclase activity by G alpha or G beta gamma, 3) although pleckstrin is a substrate for protein kinase C, the effects of pleckstrin and PMA are at least partially independent, 4) the inhibition caused by pleckstrin appears to be mediated by the PH domain at the N terminus, rather than the C terminus of the molecule, and 5) location of the two PH domains within the molecule clearly contributes to their individual activity.2+1

Animals↗