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D Pan

Publications and source records attributed to D Pan.

65 records · Page 4Linked to original sources
PubMed1992

The same dorsal binding site mediates both activation and repression in a context-dependent manner.

Like many DNA binding transcription factors, the Drosophila morphogen encoded by dorsal can both stimulate and repress promoter activity. In particular, this factor activates twist and represses zerknüllt on the ventral side of the early embryo. We find that when multiple copies of a dorsal binding site from the zerknüllt ventral repressor element are fused to a heterologous basal promoter, the resulting construct is activated by dorsal to give a ventral specific expression pattern. Thus, the ability of a dorsal binding site to mediate repression rather than activation is not an intrinsic property of the site, but depends upon its context. We also show that a hybrid promoter containing both the zerknüllt ventral repressor element and the twist ventral activator region is not ventrally active in the early embryo, demonstrating that repression is dominant over activation. Thus, the default mode of action of the dorsal protein is transcriptional activation. Additional factors may modify dorsal activity to bring about repression.

Animals↗
PubMed1991

Biosynthesis of membrane lipids in rat axons.

Compartmented cultures of sympathetic neurons from newborn rats were employed to test the hypothesis that the lipids required for maintenance and growth of axonal membranes must be synthesized in the cell body and transported to the axons. In compartmented cultures the distal axons grow into a compartment separate from that containing the cell bodies and proximal axons, in an environment free from other contaminating cells such as glial cells and fibroblasts. There is virtually no bulk flow of culture medium or small molecules between the cell body and axonal compartments. When [methyl-3H]choline was added to the cell body-containing compartment the biosynthesis of [3H]-labeled phosphatidylcholine and sphingomyelin occurred in that compartment, with a gradual transfer of lipids (less than 5% after 16 h) into the axonal compartment. Surprisingly, addition of [methyl-3H]choline to the compartment containing only the distal axons resulted in the rapid incorporation of label into phosphatidylcholine and sphingomyelin in that compartment. Little retrograde transport of labeled phosphatidylcholine and sphingomyelin (less than 15%) into the cell body compartment occurred. Moreover, there was minimal transport of the aqueous precursors of these phospholipids (e.g., choline, phosphocholine and CDP-choline) between cell compartments. Similarly, when [3H]ethanolamine was used as a phospholipid precursor, the biosynthesis of phosphatidylethanolamine occurred in the pure axons, and approximately 10% of the phosphatidylethanolamine was converted into phosphatidylcholine. Experiments with [35S]methionine demonstrated that proteins were made in the cell bodies, but not in the axons. We conclude that axons of rat sympathetic neurons have the capacity to synthesize membrane phospholipids. Thus, a significant fraction of the phospholipids supplied to the membrane during axonal growth may be synthesized locally within the growing axon.

Animals↗
PubMed1990

Many maize inbreds lack an endosperm cytosolic phosphoglucomutase.

Starch gel electrophoresis of extracts from developing maize (Zea mays L.) endosperms 22 days postpollination reveals only a single zone of phosphoglucomutase activity in the majority of the inbreds tested. The other inbreds had the expected two zones of activity. The activity that is present in all inbreds is the amyloplast isozyme while the absent form is a cytosolic enzyme. The lack of the cytosolic isozyme has no discernible phenotypic consequences.

Journal Article↗
PubMed1984

A debranching enzyme deficiency in endosperms of the sugary-1 mutants of maize.

Many of the sugary-1 mutants of maize (Zea mays L.) have the highly branched water-soluble polysaccharide, phytoglycogen, in quantities equal to or greater than starch as an endosperm storage product in mature seeds. We find that all sugary mutants investigated are deficient in debranching enzyme [alpha-(1, 6)-glucosidase] activity in endosperm tissue 23 days postpollination and suggest that this deficiency is the primary biochemical lesion leading to phytoglycogen accumulation in sugary endosperms. This would indicate that the amylopectin component of starch depends on an equilibrium between the activities of branching enzymes introducing alpha-1,6 branch points into the linear alpha-1,4 glucans and debranching enzymes. The debranching enzyme activities from nonsugary endosperms can be separated into three peaks on a hydroxyapatite column. The sugary endosperm extracts lack one of these peaks of activity while the other two fractions have much reduced activity. The embryos of developing seeds (23 days after pollination) from both sugary and nonsugary genotypes have equivalent debranching activity. The debranching enzyme activity of developing endosperms is proportional to the number of copies (0 to 3) of the nonmutant (Su) allele present suggesting that the Su allele may be the structural gene for this debranching enzyme, although this is not definitive. This identification of debranching enzyme activity as being the biochemical lesion in sugary endosperms is consistent with several previous observations on the mutant.

Journal Article↗
PubMedDate not supplied

Closed hollow-fiber bioreactor: a new approach to retroviral vector production.

BACKGROUND: The ability to obtain high-titer and large quantities of retroviral vector production in a 'closed' system would have profound implications in clinical and experimental gene therapy. METHODS: We studied the cell growth and vector production of three retroviral packaging cell lines in a variety of conditions using hollow-fiber bioreactors designed as an 'artificial capillary system' (ACS) and enhanced with the application of a hermetically sealing device for sterile welding of connecting plastic tubings. Vector titer, fetal bovine serum (FBS) concentration, volume and the duration of productivity were assessed to optimize vector production. RESULTS: In this pilot study, we observed that retroviral vector production (frozen-and-thawed) from cultures containing as low as 2.5% FBS yielded titers up to 2.2 x 10(7) cfu/ml, 14.4-fold higher than titers obtained from control dish cultures. Up to 3 liters of vector supernatant were generated during a 2-month large-scale production run. There was a potential to double this volume of higher-titer supernatant by increasing the frequency of harvest. It seemed that a lower metabolic rate (i.e. lactate production) in the packaging cell culture was associated with higher vector producing ability. CONCLUSIONS: These data demonstrated the feasibility of producing retroviral vector with enhanced titers and clinically useful quantities in a 'closed' ACS. Thus a new approach for large-scale retroviral vector production is developed.

Animals↗
PubMedDate not supplied

4D-fingerprints, universal QSAR and QSPR descriptors.

An elusive goal in the field of chemoinformatics and molecular modeling has been the generation of a set of descriptors that, once calculated for a molecule, may be used in a wide variety of applications. Since such universal descriptors are generated free from external constraints, they are inherently independent of the data set in which they are employed. The realization of a set of universal descriptors would significantly streamline such chemoinformatics tasks as virtual high-throughout screening (VHTS) and toxicity profiling. The current study reports the derivation and validation of a potential set of universal descriptors, referred to as the 4D-fingerprints. The 4D-fingerprints are derived from the 4D-molecular similarity analysis. To evaluate the applicability of the 4D-fingerprints as universal descriptors, they are used to generate descriptive QSAR models for 5 independent training sets. Each of the training sets has been analyzed previously by several varying QSAR methods, and the results of the models generated using the 4D-fingerprints are compared to the results of the previous QSAR analyses. It was found that the models generated using the 4D-fingerprints are comparable in quality, based on statistical measures of fit and test set prediction, to the previously reported models for the other QSAR methods. This finding is particularly significant considering the 4D-fingerprints are generated independent of external constraints such as alignment, while the QSAR methods used for comparison all require an alignment analysis.

Anesthetics, General↗
PubMedDate not supplied

Analysis of polycyclic aromatic hydrocarbons in cooking oil fumes.

Various samples of cooking oil fumes were analyzed to an effort to study the relationship between the high incidence of pulmonary adenocarcinoma in Chinese women and cooking oil fumes in the kitchen. Polycyclic aromatic hydrocarbons (PAHs) in samples of cooking oil fumes were extracted, chromatographed, and measured by fluorescence spectrophotometer. The samples included oil fumes from three commercial cooking oils and fumes from three catering shops. All samples contained benzo(a)pyrene (BaP) and dibenzo (a,h)anthracene (DBahA). In addition, the concentration of DBahA was 5.7 to 22.8 times higher than that of BaP in the fume samples. Concentrations of BaP and DBahA were, respectively, 0.463 and 5.736 micrograms/g in refined vegetable oil, 0.341 and 3.725 micrograms/g in soybean oil, and 0.305 and 4.565 micrograms/g in vegetable oil. Investigation of PAH concentrations at three catering shops showed that the level of BaP at a Youtiao (deep-fried twisted dough sticks) shop was 4.18 micrograms/100 m3, 2.28 micrograms/100 m3 at a Seqenma (candied fritters) workshop, and 0.49 micrograms/100 m3 at a kitchen of a restaurant; concentrations of DBahA were 33.80, 14.41, and 3.03 micrograms/100 m3, respectively. The high concentration of carcinogens, such as BaP and DBahA, in cooking oil fumes might help explain why Chinese women, who spend more time exposed to cooking oil fumes than men, have a high incidence of pulmonary adenocarcinoma.

Adenocarcinoma↗