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Biomedical subjects

J Dean

Publications and source records attributed to J Dean.

At least 73 records · Page 4Linked to original sources
PubMed1996

Studies on the interaction of placental anticoagulant protein I, beta 2 glycoprotein 1, and antiphospholipid antibodies in the prothrombinase reaction and in the solid phase anticardiolipin assays.

Recently it has been suggested that antiphospholipid antibodies may not be specific for phospholipids but directed to beta2glycoprotein 1 (beta2GP1), phospholipid-beta2GP1 complexes, prothrombin, or prothrombin-phospholipid complexes. To explore this issue further, we examined the influence of two phospholipid binding proteins, annexin V (placental anticoagulant protein I (PAP I)) and beta2GP1, on the activity of immunoglobulin G (IgG) fractions from patients with antiphospholipid syndrome (APS), both in the prothrombin-thrombin conversion assay and in the anticardiolipin enzyme-linked immunosorbent assay (ELISA). Results showed that each of eight IgG-APS; fractions, as well as PAP I and beta2GP1, individually inhibited the prothrombinase reaction. When IgG-APS samples were combined with PAP I or beta2GP1, or both PAP I and beta2GP1, inhibition of the prothrombinase reaction was additive. In the anticardiolipin ELISA, PAP I inhibited IgG-APS binding to cardiolipin, but beta2GP1 enhanced IgG-APS binding to cardiolipin. The "enhancing" effect of beta2GP1 in the ELISA system was neutralized by PAP I, an effect partially overcome by increasing the concentration of beta2GP1. Similar results were observed when affinity-purified anticardiolipin antibodies were used in place of whole IgG-APS preparations. These data indicate that IgG preparations obtained from the 8 patients with APS recognize similar epitopes; on anionic phospholipids in the anticardiolipin test and in the prothrombin-thrombin conversion assay. These data do not exclude the possibility that the IgG preparations may bind prothrombin-phospholipid or beta2GP1-phospholipid complexes.

Annexin A5↗
PubMed1996

The molecular genetics of the zona pellucida: mouse mutations and infertility.

The zona pellucida is an extracellular matrix surrounding growing oocytes, ovulated eggs and the preimplantation embryo. After mediating the relatively species-specific events of fertilization, the zona pellucida provides a post-fertilization block to polyspermy and protects the growing embryo as it passes down the oviduct. The genes that encode the three zona pellucida proteins (ZP1, ZP2, ZP3) have been characterized in mouse and human. The ability to genetically manipulate the zona pellucida genes in mouse models has enhanced our knowledge of zona pellucida structure and function in vivo and may translate into a better understanding of human fertility.

Animals↗
PubMed1996

Mice homozygous for an insertional mutation in the Zp3 gene lack a zona pellucida and are infertile.

Mammalian oocytes synthesize and secrete a zona pellucida that surrounds the growing oocytes, ovulated eggs and preimplantation embryos. The extracellular zona matrix is composed of three glycoproteins (ZP1, ZP2, ZP3) that are involved in folliculogenesis, species-specific fertilization, and passage of the early embryo down the oviduct. We have established a mouse line in which Zp3 has been inactivated by homologous recombination with an insertional mutation. Neither Zp3 transcripts nor ZP3 protein was detected in female mice homozygous for the mutation (Zp3-/-), whereas both ZP1 and ZP2 were present in mutant oocytes. Homozygous mutant Zp3-/- mice had follicles with germinal-vesicle-intact oocytes but that lacked a zona pellucida matrix and had a disorganized corona radiata. Although mutant oocytes underwent germinal vesicle breakdown (GVBD) prior to ovulation, the cumulus-oocyte complex was markedly disrupted and the oocytes were often separate from the cumulus cells. After hormone-induced ovulation, cumulus masses were present in the oviducts of homozygous mutant mice, but zona-free eggs were observed in only half of the females and, in these, less than 10% of the normal number [correction of mumber] of eggs were detected. No zona-free 2-cell embryos were recovered from homozygous mutant Zp3-/- female mice after mating with males proven to be fertile, and none became visibly pregnant or produced offspring. These results demonstrate that a genetic defect in a zona pellucida gene causes infertility and, given the conserved nature of the zona pellucida, a similar phenotype is expected in other mammals.

Animals↗
PubMed1996

Molecular genetics of the zona pellucida: implications for immunocontraceptive strategies.

Successful immunocontraceptive agents must prevent fertilization without compromising the health of the individual exposed to immunization. The zona pellucida, which surrounds all mammalian eggs and is unique to the female gamete, represents a potential target for immunocontraception. Mouse and human zonae pellucidae are composed of three glycoproteins, designated ZP1, ZP2 and ZP3. The genes are conserved and the transcripts that encode the zona proteins have been characterized in both species. In mice, the expression of the zona genes is oocyte specific. The recent elucidation of the primary structure of the zona proteins in a number of species has provided critical information for the rational design of a contraceptive vaccine. We and others have demonstrated that both passive and active immunization strategies that target individual zona proteins can prevent fertilization. Although various contraceptive strategies have been tested in a laboratory setting, the applicability of these protocols to humans remains to be determined. The recent revolution in transgenesis coupled with the cloning of the human zona pellucida genes provide the means to produce animal models for testing immunocontraceptive strategies that target human zona proteins. These models could provide a system for the initial evaluation of vaccine candidates prior to trials in primates.

Animals↗
PubMed1995

Mouse Zp1 encodes a zona pellucida protein homologous to egg envelope proteins in mammals and fish.

Zp1 encodes one of the three major glycoproteins of the zona pellucida, an extracellular matrix that surrounds growing oocytes, ovulated eggs, and preimplantation embryos. The mouse gene is composed of 12 exons ranging in size from 82 to 364 base pairs and spans 6.5 kilobase pairs on chromosome 19 (2.13 +/- 1.5 centimorgans distal to D19Bir1). The Zp1 exon map is similar to ZPB, a human orthologue, and an E-box (CANNTG), implicated in oocyte-specific gene expression of mouse Zp2 and Zp3, is similarly located upstream of the transcription start site. The single copy Zp1 gene encodes a 623-amino acid protein, the carboxyl-terminal half of which is significantly similar to a corresponding region of mouse ZP2. The conservation of this same region in a fish egg envelope protein suggests that not only has this protein domain been duplicated in mammals but that it has been conserved and used as an egg envelope protein in species that diverged 650 million years ago.

Amino Acid Sequence↗
PubMed1995

POM-ZP3, a bipartite transcript derived from human ZP3 and a POM121 homologue.

Human POM-ZP3 is a novel bipartite RNA transcript that is derived from a gene homologous to rat POM121 (a nuclear pore membrane protein) and ZP3 (a sperm receptor ligand in the zona pellucida). The 5' region is 77% identical to the 5' end of the coding region of rat POM121 and appears to represent a partial duplication of a gene encoding a human homologue of this rodent gene. The 3' end of the POM-ZP3 transcript is 99% identical to ZP3 and appears to have arisen from a duplication of the last four exons (exons 5-8) of ZP3. Using Northern blots and RT-PCR, POM-ZP3 transcripts were detected in human ovaries, testes, spleen, thymus, lymphocytes, prostate, and intestines. The longest open reading frame encodes a conceptual protein of 210 amino acids, the first 76 of which are 83% identical to residues 241-315 of rat POM121. The next 125 amino acids are 98% identical to residues 239-363 of the 424-amino-acid human ZP3 protein. By fluorescence in situ hybridization, genomic fragments of ZP3 and a human homologue of POM121 were localized to chromosome 7q11.23. Taken together, these data suggest that partial duplications of human ZP3 and a POM121-like gene have resulted in a fusion transcript, POM-ZP3, that is expressed in multiple human tissues.

Amino Acid Sequence↗
PubMed1995

Inhibition of zona pellucida gene expression by antisense oligonucleotides injected into mouse oocytes.

During murine oogenesis, the zona pellucida proteins (ZP1, ZP2, and ZP3) are synthesized and secreted to form an extracellular matrix that surrounds the oocyte and mediates specific biological functions essential to mammalian fertilization and early development. To investigate the relationship among the zona proteins during zona matrix assembly, we have undertaken to inhibit de novo biosynthesis of specific zona proteins with antisense oligonucleotides complementary to the 5'-ends of ZP2 (nucleotide position 19-42) and ZP3 (nucleotide 21-44) mRNAs. When injected into the cytoplasm of growing mouse oocytes, the antisense oligonucleotides targeted specific zona mRNAs for degradation, as confirmed by a RNase protection assay. Individual zona pellucida protein synthesis was followed by immunoprecipitation with ZP2- and ZP3-specific monoclonal antibodies. New zona protein synthesis from the targeted mRNA was abolished, but nontargeted zona protein continued to be synthesized. Interestingly, abolishment of either ZP2 or ZP3 protein synthesis prevented the incorporation of the other protein into the extracellular zona matrix. These results suggest that ZP2 and ZP3 proteins are independent of each other in their biosynthesis but are dependent upon each other for their incorporation into the zona pellucida matrix. This study provides an experimental system in which destruction of a targeted mRNA generates a transient loss-of-expression phenotype during mouse oocyte growth.

Animals↗
PubMed1995

A modular artificial neural net for controlling a six-legged walking system.

A system that controls the leg movement of an animal or a robot walking over irregular ground has to ensure stable support for the body and at the same time propel it forward. To do so, it has to react adaptively to unpredictable features of the environment. As part of our study of the underlying mechanisms, we present here a model for the control of the leg movement of a 6-legged walking system. The model is based on biological data obtained from the stick insect. It represents a combined treatment of realistic kinematics and biologically motivated, adaptive gait generation. The model extends a previous algorithmic model by substituting simple networks of artificial neurons for the algorithms previously used to control leg state and interleg coordination. Each system controlling an individual leg consists of three subnets. A hierarchically superior net contains two sensory and two 'premotor' units; it rhythmically suppresses the output of one or the other of the two subordinate nets. These are continuously active. They might be called the 'swing module' and the 'stance module' because they are responsible for controlling the swing (return stroke) and the stance (power stroke) movements, respectively. The swing module consists of three motor units and seven sensory units. It can produce appropriate return stroke movements for a broad range of initial and final positions, can cope with mechanical disturbances of the leg movement, and is able to react to an obstacle which hinders the normal performance of the swing movement. The complete model is able to walk at different speeds over irregular surfaces. The control system rapidly reestablishes a stable gait when the movement of the legs is disturbed.

Gait↗
PubMed1995

Reversion of duck hepatitis B virus DNA replication in vivo following cessation of treatment with the nucleoside analogue ganciclovir.

In order to define, in more detail, the virological events which occur after completion of antiviral chemotherapy, ducks congenitally infected with the duck hepatitis B virus (DHBV) were treated for 4 weeks with the nucleoside analogue ganciclovir and followed up over a 7-day period. Specimens of serum and liver were collected daily during follow-up for virological analysis. Treatment resulted in a substantial reduction in both viraemia and liver DHBV DNA replicative intermediates. However, after cessation of treatment, viraemia returned to detectable levels within 4 days. In the liver, the viral supercoiled DNA (SC DNA) was the form least affected by therapy and returned to near control levels by day 2 post-treatment. The other hepatic replicative intermediates reached pretreatment levels within 4 days of cessation of therapy. This study has defined the kinetics of relapse of viral replication after completion of antiviral therapy in the duck hepatitis B model. Of all viral replicative forms, the SC DNA appears to be the one which is most resistant to nucleoside analogue therapy and is presumably responsible for the relapse phenomenon observed post-treatment.

Animals↗
PubMed1995

Folic acid absorption in women with a history of pregnancy with neural tube defect.

Folic acid absorption was compared in nonpregnant women with a history of pregnancy with a neural tube defect (cases)(n = 10) with that of control women (n = 10) with a normal pregnancy history. [2H4]folic acid was administered in an oral dose (400 micrograms) to fasting case and control subjects after a 30-d saturation protocol involving daily ingestion of two 1-mg folic acid supplements. Serum and red blood cell folate concentrations were not different for case and control subjects before or during the saturation protocol (P > 0.05). The percentage (x +/- SD) of the oral dose of [2H4]folic acid excreted in 24-h urine collections postdose was not different (P > 0.05) for case compared with control subjects (9.05 +/- 2.25% and 11.10 +/- 3.41%, respectively). These data suggest that the absorption of folic acid routinely consumed in supplements and fortified food products is not impaired in women with a history of a pregnancy with a neural tube defect. Further case-controlled studies are needed to compare the absorption of the predominant dietary form of the vitamin.

Administration, Oral↗
PubMed1995

The covalently closed duplex form of the hepadnavirus genome exists in situ as a heterogeneous population of viral minichromosomes.

Replication of hepadnaviruses requires a persistent population of covalently closed circular (CCC) DNA molecules in the nucleus of the infected cell. It is widely accepted that the vital role of this molecule is to be the sole DNA template for the synthesis by RNA polymerase II of all viral transcripts throughout the infection process. Since the transcriptional activity of eukaryotic nuclear DNA is considered to be determined in part by its specific organization as chromatin, the nucleoprotein disposition of the hepadnavirus CCC DNA was investigated. These studies were undertaken on the duck hepatitis B virus (DHBV) CCC DNA present in the liver cell nuclei of DHBV-infected ducks. The organization and protein associations of the DHBV CCC DNA in situ were inferred from sedimentation, micrococcal nuclease digestion, and DNA superhelicity analyses. These three lines of investigation demonstrate that the DHBV CCC DNA is stably associated with proteins in the nuclei of infected liver cells. Moreover, they provide compelling evidence that the viral nucleoprotein complex is indeed a minichromosome composed of classical nucleosomes but in arrays that are atypical for chromatin. When the DHBV chromatin is digested with micrococcal nuclease, a ladder of viral DNA fragments that exhibits a 150-bp repeat is produced. This profile for the viral chromatin is obtained from the same nuclei in which the duck chromatin shows the standard 200-bp ladder. The superhelicity of the DHBV CCC DNA ranges from 0 to 20 negative supertwists per molecule, with all possible 21 topoisomers present in each DNA preparation. The 21 topoisomers of DHBV CCC DNA are inferred to derive from an identically diverse array of viral minichromosomes. In the DHBV minichromosomes composed of 20 nucleosomes, 96.7% of the viral DNA is calculated to be compacted into these chromatin subunits spaced on average by 5 bp of linker DNA; other minichromosomes contain fewer nucleosomes and proportionately more linker DNA. Two major subpopulations of DHBV minichromosomes are detected with comparable prevalence. The two groups correspond to minichromosomes which contain essentially a full or half complement of nucleosomes. The functional significance of this minichromosome diversity is unknown but is suggestive of transcriptional regulation of the viral DNA template.

Animals↗
PubMed1995

Aortic distensibility and stiffness index measured by magnetic resonance imaging in patients with Marfan's syndrome.

OBJECTIVES: To use magnetic resonance imaging to measure the elastic properties of the aorta of adults with Marfan's syndrome and to compare these results with those obtained by echocardiography. PATIENTS AND METHODS: 12 patients with Marfan's syndrome and 12 controls matched for age. Transverse luminal areas of the ascending and descending aorta were measured using electrocardiographic gated magnetic resonance imaging. Echocardiography was used to measure the diameter of the ascending aorta and aortic arch in patients with Marfan's syndrome. Blood pressure was measured during both scans. RESULTS: In diastole, transverse luminal areas of the ascending and descending aorta were significantly greater in patients with Marfan's syndrome when measured by magnetic resonance imaging and corrected for body surface area; P < 0.02 and P < 0.05 respectively. Patients with Marfan's syndrome had a higher stiffness index (112.77 v 5.78, P < 0.05) and a lower distensibility (0.0066 v 0.0105, P < 0.05) than controls. Results produced by MRI and echocardiography were not significantly different. CONCLUSIONS: Magnetic resonance imaging gives good quality reproducible images of the ascending and descending aorta. In patients with Marfan's syndrome, aortic distensibility and stiffness index measured by magnetic resonance imaging were abnormal (but did not always relate directly to the size of the aorta.

Adult↗
PubMed1995

Coordinate expression of the three zona pellucida genes during mouse oogenesis.

The mammalian zona pellucida is an extracellular matrix that surrounds growing oocytes, ovulated eggs and early embryos. The mouse zona is composed of three sulfated glycoproteins: ZP1, ZP2 and ZP3. Each is critically involved in fertilization, the postfertilization block to polyspermy and protection of the preimplantation embryo. We have previously isolated cDNAs encoding mouse ZP2 and ZP3 and now report the isolation of a full-length cDNA encoding ZP1. Mouse ZP1 is composed of a 623 amino acid polypeptide chain with a signal peptide and a carboxyl terminal transmembrane domain, typical of all zona proteins. Sequence comparison demonstrate that mouse ZP1 is an orthologue of a rabbit zona protein, R55. The expression of R55 has been reported previously in both oocytes and granulosa cells. However, by northern analysis and in situ hybridization with 33P-labelled antisense probes to each of the three mouse zona mRNAs, we have determined that the expression of each mouse zona gene is restricted to the oocyte. ZP2 transcripts, but not ZP1 or ZP3, are detected in resting (15 microns diameter) oocytes, and all three zona transcripts coordinately accumulate as oocytes begin to grow. Together they represent approximately 1.5% of the total poly(A)+ RNA in 50-60 microns oocytes. In the latter stages of oogenesis, their abundance declines and each zona transcript is present in ovulated eggs at less than 5% of its maximal level. No zona transcripts were detected above background signal in granulosa cells. We conclude that, in mice, the three zona pellucida genes are expressed in a coordinate, oocyte-specific manner during the growth phase of oogenesis. Our data support the hypothesis that the transcription of the zona genes is controlled, in part, by shared regulatory element(s).

Animals↗
PubMed1995

Effect of treatment with a hydroxymethylglutaryl coenzyme A reductase inhibitor on fasting and postprandial plasma lipoproteins and cholesteryl ester transfer activity in patients with NIDDM.

Patients with non-insulin-dependent diabetes mellitus (NIDDM) have a greater risk of developing coronary heart disease than would be expected from a similar degree of hyperlipidemia in nondiabetic populations. Accelerated transfer of cholesteryl esters (CET) from high-density lipoprotein (HDL) to low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL), a process that is associated with atherosclerosis, may be a possible explanation for this. CET, plasma lipoprotein concentration, and mass in the fasting and postprandial state have been examined in 31 hyperlipidemic patients with NIDDM before and after 8 weeks of treatment with the hydroxymethylglutaryl (HMG)-coenzyme A (CoA) reductase inhibitor pravastatin in a double-blind, placebo-controlled, parallel group study. Body mass index, glycemic control, and blood pressure remained unaltered during the study period. Compared with placebo, pravastatin decreased fasting serum cholesterol (P < 0.001) and LDL cholesterol (P < 0.002) levels. The high basal CET (34.4 +/- 13.1 nmol.ml-1.h-1) was decreased significantly by pravastatin treatment (27.5 +/- 13.7 nmol.ml-1.h-1, P = 0.013). There was a fall in the total cholesterol, free cholesterol, and phospholipid content of the Sf 0-12, 20-60, and 60-400 lipoproteins (all P = 0.001). Lecithin: cholesterol acyl transferase activity was not altered. The postprandial increase in VLDL cholesterol 5 h after a standardized mixed meal was attenuated after pravastatin treatment (P = 0.011). Inhibition of hepatic cholesterol synthesis with an HMG-CoA reductase inhibitor in hyperlipidemic patients with NIDDM decreased serum cholesterol content of triglyceride-rich lipoprotein, thereby decreasing the transfer of cholesteryl ester from HDL to LDL and VLDL.

Adult↗
PubMed1995

General practitioners' tacit and stated policies in the prescription of lipid lowering agents.

BACKGROUND: Research into general practitioners' prescribing behaviour with regard to lipid lowering agents has relied on survey methods which presume that doctors have insight into their prescribing behaviour and can describe it accurately. AIM: This study set out to measure the tacit policies used by general practitioners in prescribing lipid lowering agents and to compare these with their stated policies. METHOD: Effects of 13 separate cues on decisions to prescribe were examined. The cues included cholesterol levels and a number of associated risk factors for coronary heart disease. Doctors rated 130 imaginary cases presented by a computer. Thirty five general practitioners in the Plymouth area participated in the study. Their ages ranged from 31 to 55 years and all but four were men. The raw data in each case was a rating of the likelihood that the doctor would prescribe for the patient described. These were converted into statistical weightings by use of multiple linear regression. The pattern of (standardized) weights constituted the tacit policy for each doctor. Stated policies were measured in a subsequent interview by asking doctors to rate the influence of each cue. RESULTS: Both tacit and stated policies diverged widely between different doctors. Most doctors overestimated the number of cues that had actually influenced their decisions, and many believed that they had taken into account associated factors for coronary heart disease when they had not. On lifestyle related risks doctors were generally less likely to treat overweight people and most stated this as their policy. Most were also less likely to treat smokers but some had the opposite policy. Those less likely to treat smokers were also less likely to treat obese patients. There was also considerable variation in the extent to which the doctors took account of the attitude of the patient to receiving treatment. CONCLUSION: Doctors' policies are highly variable and particularly inconsistent in the treatment of smokers. Relevant risk factors may be ignored--even though they are understood--because the risk assessment involved is too psychologically complex a task to be performed intuitively. Decision aids and clear protocols are needed in this area.

Adult↗