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Biomedical subjects

J Yu

Publications and source records attributed to J Yu.

At least 649 records · Page 36Linked to original sources
PubMed1995

Absence of PsaC subunit allows assembly of photosystem I core but prevents the binding of PsaD and PsaE in Synechocystis sp. PCC6803.

In photosystem I (PSI) of oxygenic photosynthetic organisms the psaC polypeptide, encoded by the psaC gene, provides the ligands for two [4Fe-4S] clusters, FA and FB. Unlike other cyanobacteria, two different psaC genes have been reported in the cyanobacterium Synechocystis 6803, one (copy 1) with a deduced amino acid sequence identical to that of tobacco and another (copy 2) with a deduced amino acid sequence similar to those reported for other cyanobacteria. Insertion of a gene encoding kanamycin resistance into copy 2 resulted in a photosynthesis-deficient strain, CDK25, lacking the PsaC, PsaD and PsaE polypeptides in isolated thylakoid membranes, while the PsaA/PsaB and PsaF subunits were found. Growth of the mutant cells was indistinguishable from that of wild-type cells under light-activated heterotrophic growth (LAHG). A reversible P700+ signal was detected by EPR spectroscopy in the isolated thylakoids during illumination at low temperature. Under these conditions, the EPR signals attributed to FA and FB were absent in the mutant strain, but a reversible Fx signal was present with broad resonances at g = 2.079, 1.903, and 1.784. Addition of PsaC and PsaD proteins to the thylakoids gave rise to resonances at g = 2.046, 1.936, 1.922, and 1.880; these values are characteristic of an interaction-type spectrum of FA- and FB-. In room-temperature optical spectroscopic analysis, addition of PsaC and PsaD to the thylakoids also restored a 30 ms kinetic transient which is characteristic of the P700+ [FA/FB]- backreaction. Expression of copy 1 was not detected in cells grown under LAHG and under mixotrophic conditions. These results demonstrate that copy 2 encodes the PsaC polypeptide in PSI in Synechocystis 6803, while copy 1 is not involved in PSI; that the PsaC polypeptide is necessary for stable assembly of PsaD and PsaE into PSI complex in vivo; and that PsaC, PsaD and PsaE are not needed for assembly of PsaA-PsaB dimer and electron transport from P700 to Fx.

Bacterial Proteins↗
PubMed1995

Hybridization of genes involved in aflatoxin biosynthesis to DNA of aflatoxigenic and non-aflatoxigenic aspergilli.

Southern blots of DNA from a number of aspergilli belonging to Aspergillus section Flavi, including aflatoxin-producing and non-aflatoxigenic isolates of A. flavus and A. parasiticus, were probed with the aflatoxin pathway genes aflR and omt-1. DNA of all A. flavus, A. parasiticus and A. sojae isolates examined hybridized with both genes. None of the A. oryzae isolates examined hybridized to the aflR probe and one of the three did not hybridize to the omt-1 probe. None of the A. tamarii isolates examined hybridized to either gene. Our results suggest that some isolates in this section do not produce aflatoxin because they lack at least one of the genes necessary for biosynthesis, and that non-producing A. flavus, A. parasiticus and A. sojae strains either lack a gene we did not examine or have genes that are not being expressed.

Aflatoxins↗
PubMed1995

Postnatal migration of neurons and formation of laminae in rat cerebral cortex.

Migration of neurons and formation of laminae in the developing neocortex were studied by means of thymidine autoradiography. Timed pregnant rats received a single pulse injection of [3H]thymidine in the morning of embryonic day (E)13, 14, 15, 16, 17, 18 or 19. Pups were killed on postnatal day (P)0, 1, 2, 3, 4, 6, 10, 30, or 60 and brains were processed for autoradiography. Neurons in posterior (visual) cortical areas labeled by [3H]thymidine administration on E13 or E14 were found predominantly in the cortical subplate; cells labeled on E15 in layer VI; cells labeled on E16 in layers VI and V, cells labeled on E17 in layers V and IV; E18 in layers IV and III; and E19 in layers III and II. By the day of birth (P0), neurons labeled from E13-16 injections were already in their mature laminae in cortex. Many of the cells labeled on E17 were still situated within the cell-dense cortical plate (CP) at P0, and within layer V by P1. Cells labeled on E18 were found in the most superficial part of the CP on P0, in the deep part of the CP on P1, and formed layer IV on P2 and P3. At P0, many E19 labeled cells appeared to be in migration to the cortex and were found in the CP on P1, in layer III by P4, and in layer II by P6. Cells in the auditory cortex labeled by [3H]thymidine injections on a particular day were situated more superficially than comparable labeled cells in the visual cortex, indicating a lateral to medial gradient in which the auditory cortex is formed earlier than the visual cortex. Distributions of labeled cells in the somatosensory cortex were similar to those in the visual cortex. These data provide a detailed and comprehensive description of the position of varied populations of cortical neurons during the early postnatal period, as well as a description of the formation of cortical laminae at times when major systems of afferents are growing into the cortex and making synaptic connections with their target cells.

Afferent Pathways↗
PubMed1995

YAC contig mapping of six expressed sequences encoded by human chromosome 21.

Six cDNA clones from human chromosome 21 have been mapped in a set of complete YAC contig spanning the entire chromosome 21q. The mapping positions between two STSs on the YAC contig and the NotI coordinates starting from the telomere of 21q were determined for the cDNA clones. The YAC contig mapping positions agree well with those using a comprehensive somatic cell hybrid mapping panel.

Animals↗
PubMed1995

Three region-specific microdissection libraries for the long arm of human chromosome 2, regions q33-q35, q31-q32, and q23-q24.

Three region-specific libraries have been constructed from the long arm of human chromosome 2, including regions 2q33-35 (2Q2 library), 2q31-32 (2Q3) and 2q23-24 (2Q4). Chromosome microdissection and the MboI linker-adaptor microcloning techniques were used in constructing these libraries. The libraries comprised hundreds of thousands of microclones in each library. Approximately half of the microclones in the library contained unique or low-copy number sequence inserts. The insert sizes ranged between 50 and 800 bp, with a mean of 130-190 bp. Southern blot analysis of individual unique sequence microclones showed that 70-94% of the microclones were derived from the dissected region. 31 unique sequence microclones from the 2Q2 library, 31 from 2Q3, and 30 from 2Q4, were analyzed for insert sizes, the hybridizing genomic HindIII fragment sizes, and cross-hybridization to rodent species. These libraries and the short insert microclones derived from the libraries should be useful for high resolution physical mapping, sequence-ready reagents for large scale genomic sequencing, and positional cloning of disease-related genes assigned to these regions, e.g. the recessive familial amyotrophic lateral sclerosis assigned to 2q33-q35, and a type I diabetes susceptibility gene to 2q31-q33.

Amyotrophic Lateral Sclerosis↗
PubMed1995

Qualitative analysis of Kolmogorov-type models of predator-prey systems.

The qualitative behaviors of Kolmogorov-type models are investigated under assumptions that are consistent with models of predator-prey systems and biologically realistic. The main purpose of this paper is to prove the boundedness of solutions and to give criteria for the existence of limit cycles for the system. In the case that the positive equilibrium is locally asymptotically stable, an example shows that there could be more limit cycles. This example serves as a counterexample to the global stability criterion of Huang.

Animals↗
PubMed1995

Senile plaques stimulate microglia to release a neurotoxin found in Alzheimer brain.

Senile plaques found in the brains of patients with Alzheimer's disease (AD) are surrounded by clusters of reactive microglia. Isolated human microglia placed in contact with plaques in vitro are activated to release a factor which is toxic to neurons. This same neurotoxin is found in AD brain tissue and causes damage to pyramidal neurons in vivo when infused into rat hippocampus. Highest concentrations of the neurotoxin are in those brain structures most burdened by reactive microglia, suggesting that plaque-activated cells contribute to the neuronal damage and impaired cognition seen in patients with Alzheimer's dementia.

Alzheimer Disease↗
PubMed1995

Synthesis of 2-[131I]iodophenyl-metyrapone using Cu(I)-assisted nucleophilic exchange labelling: study of the reaction conditions.

2-Bromophenyl-metyrapone has been synthesized as a precursor for Cu(I)-assisted labelling with radioiodine. A labelling yield of > 95% was obtained and the specific activity of the purified product was 120 GBq/mumol. The iodo for bromo exchange requires an excess of reducing agents to maintain the Cu(I) redox potential. The effects of the amount of reactants, temperature and time were studied. The labelling yield showed a direct dependence on the amount of precursor and Cu(+)-catalyst used for the reaction, and an increase with reaction time (optimal at 60 min) and temperature (optimal at 100 degrees C). Studies of the stability, lipophilicity and binding of 2-[131I]iodophenyl-metyrapone to serum protein indicated high in vitro stability, high lipophilicity (log P = 2.19) and a loose association with serum proteins.

Animals↗
PubMed1995

Localization of metalloporphyrin-induced "specific" enhancement in experimental liver tumors: comparison of magnetic resonance imaging, microangiographic, and histologic findings.

RATIONALE AND OBJECTIVES: We investigated the tumor specificity of gadolinium mesoporphyrin (Gd-MP) and manganese tetraphenylporphyrin (Mn-TPP) as magnetic resonance (MR) imaging contrast agents. METHODS: Fifteen rats with multiple hepatocellular carcinomas and eight rats with implanted Novikoff hepatomas were given intravenous injections of either Gd-MP or Mn-TPP at 0.05 mmol/kg, which was compared with nonspecific gadopentetate dimeglumine (0.3 mmol/kg). T1-weighted spin-echo images were obtained before and up to 48 hr after injection and compared with corresponding microangiograms and histologic specimens. The relative enhancement of organs and tumors was plotted as a function of time. RESULTS: Initially, both metalloporphyrins behaved as nonspecific agents, similar to gadopentetate dimeglumine, and enhanced the tumor by perfusion and diffusion. However, metalloporphyrins, but not gadopentetate dimeglumine, caused a delayed (> or = 3 hr) enhancement in some compartments of certain lesions. The MR imaging-microangiography-histology matching technique revealed that those compartments were actually nonviable components, including necrosis (n = 10), thrombosis (n = 7), and cystic secretion (n = 3), but not viable tumor tissue. CONCLUSION: Metalloporphyrins did not prove to be tumor specific. However, the observed affinity for nonviable tissue has elicited other potential applications for these agents.

Angiography↗
PubMed1995

Normal pressure hydrocephalus: an analysis of aetiology and response to shunting based on mathematical modeling.

The dynamics which maintain the state of enlarged cerebral ventricles and normal intracranial pressures (normal pressure hydrocephalus) are not completely understood, making the response to cerebrospinal fluid diversion difficult to predict. Using our previously described mathematical model of intracranial physiology which allows nonlinear relationships of pressure, volume, and flow in 7 distinct compartments, we desired to determine factors which could be responsible for the development and maintenance of the steady state of normal pressure hydrocephalus. Using typical starting values for CSF volume, pressure, and flow, the model indicates that this condition cannot be sustained, in spite of high CSF outflow resistance, unless capillary flow resistance is elevated. This condition can be the result of arterial hypertension. The additional modeling of a CSF diversion device demonstrates predicted time courses for ventricular size reduction which are consistent with clinical observations. We conclude that certain vascular conditions may allow for the maintenance of an enlarged ventricular size, and that mathematical modeling can assist in identifying factors for clinical study that may maintain normal pressure hydrocephalus even after treatment by CSF diversion.

Cerebral Ventricles↗
PubMed1995

Effect of Helicobacter mustelae infection on ferret gastric epithelial cell proliferation.

The effect of Helicobacter mustelae infection on gastric epithelial proliferation was studied in ferrets colonized with H.mustelae and specific pathogen-free (SPF) ferrets not infected with H.mustelae. Thirteen H. mustelae-infected ferrets between the ages of 13 and 32 months and 16 SPF ferrets between 6 and 18 months were analyzed. Bacterial cultures, urease tests and Warthin-Starry stains were used to identify H.mustelae. Tissues obtained from the antrum and the body regions of the stomach were assayed by proliferating cell nuclear antigen (PCNA) immunohistochemistry and measured using a computerized color image analysis system. PCNA-expressing gastric epithelia in the antrum and the body regions were significantly increased in the H.mustelae-infected ferrets versus the SPF ferrets (P < 0.001). PCNA positivity in the antrum regions of both the H.mustelae-infected ferrets and SPF ferrets was significantly higher than that of the body regions (P < 0.001). Comparison of the histopathology of infected ferrets indicated that PCNA positivity correlated with the histological severity of gastritis. This study suggests that cell proliferation in ferret gastric mucosa increases with H.mustelae infection and provides evidence that PCNA is a useful biomarker for studying the changes in cell kinetics in the ferret stomach. The data also further support the use of the H.mustelae-infected ferret as an animal model for studying the pathogenesis of Helicobacter pylori-induced gastric diseases of humans.

Animals↗
PubMed1995

Long-term supplementation of canthaxanthin does not inhibit gastric epithelial cell proliferation in Helicobacter mustelae-infected ferrets.

The effect of canthaxanthin (CX), a nonprovitamin A carotenoid, on gastric epithelial proliferation was studied in ferrets colonized with Helicobacter mustelae, which causes a chronic gastritis and an increased gastric epithelial cell proliferation. Seven spayed female ferrets were dosed by gavage with CX beadlets (50 mg/kg body wt, 5 d/wk) over 2 y, whereas seven control animals were given placebo beadlets. At the end of the 2-y-period, ferrets were killed, and gastric tissues were obtained from the antrum and body regions. A cell-proliferating biomarker, proliferating cell nuclear antigen (PCNA), was assayed by immunohistochemistry. The PCNA positivity was measured by a computer-based image analysis system. Serum concentrations of carotenoids, retinoids and tocopherols were analyzed by HPLC. Serum antioxidant status was measured by the oxygen radical absorbance capacity (ORAC) assay. The PCNA positivity in both antrum and body regions was not significantly different between CX-fed ferrets and controls. Serum CX concentrations were significantly higher in CX-fed ferrets vs. controls (P < 0.001), whereas levels of other carotenoids, retinoids and tocopherols were not significantly different. The ORAC values were not significant different between groups. This study does not suggest inhibitory effects of CX on gastric epithelial cell proliferation in H. mustelae infected ferrets.

Animals↗
PubMed1995

Style, consumption, and problem drinking: a measurement model.

Yu and Williford (J. Drug Issues 22:75-90, 1992) report from a structural study that drinking style is the best predictor of problem drinking. This study further examines a measurement model on drinking style, alcohol consumption, and problem drinking. Four measures are specified for drinking style, three for alcohol consumption, and two for problem drinking. The maximum-likelihood procedure through the LISREL program is used to reproduce the observed correlations by allowing correlations among systematic measurement errors. Strong associations are noted among drinking style, alcohol consumption, and problem drinking. The analysis suggests that the style of drinking should be included in research on problem drinking. Implications of the findings and future research issues are discussed.

Adult↗
PubMed1995

Comparative mapping of aflatoxin pathway gene clusters in Aspergillus parasiticus and Aspergillus flavus.

Aflatoxins are toxic and carcinogenic secondary metabolites produced by the fungi Aspergillus flavus and A. parasiticus. Aflatoxins are synthesized by condensation of acetate units; their synthesis is estimated to involve at least 16 different enzymes. In this study we have shown that at least nine genes involved in the aflatoxin biosynthetic pathway are located within a 60-kb DNA fragment. Four of these genes, nor-1, aflR, ver-1, and omtA (previously named omt-1), have been cloned in A. flavus and A. parasiticus. In addition, five other genes, pksA, uvm8, aad, ord-1, and ord-2 have been recently cloned in A. parasiticus. The pksA, aad, and uvm8 genes exhibit sequence homologies to polyketide synthase, aryl-alcohol dehydrogenase, and fatty acid synthase genes, respectively. The cDNA sequences of ord-1 and ord-2 genes, which may be involved in later steps of aflatoxin biosynthesis, have been determined; the ord-1 gene product exhibits homology to cytochrome P-450-type enzymes. By characterizing the overlapping regions of the DNA inserts in different cosmid and lambda DNA clones, we have determined the order of these aflatoxin pathway genes within this 60-kb DNA region to be pksA, nor-1, uvm8, aflR, aad, ver-1, ord-1, ord-2, and omtA in A. parasiticus and nor-1, aflR, ver-1, ord-1, ord-2, and omtA in A. flavus. The order is related to the order in enzymatic steps required for aflatoxin biosynthesis. The physical distances (in kilobase pairs) and the directions of transcription of these genes have been determined for both aflatoxigenic species.

Aflatoxins↗