Pulsation of nuclei in insect oocytes is reversibly inhibited by cytochalasin B

Oocyte nuclei of the dipteran insect Heteropeza pygmaea display swift pulsating movements during in vitro follicle formation in the ovaries. Low doses of cytochalasin B (CB) completely inhibit the nuclear movements within a few minutes and cause the nuclei to assume spherical shapes. If the drug is removed, nuclear pulsation is resumed within 5–10 min. Phalloidin and colchicine do not affect the nuclear movements. Actin is shown by indirect immunofluorescence microscopy to be present in considerable amounts all over the cytoplasm of the oocytes. It is concluded that microfilaments are responsible for pulsation of the oocyte nuclei, whereas microtubules are not involved.     

Effect of pH and bicarbonate on phosphoenolpyruvate carboxykinase and glutaminase mRNA levels in cultured renal epithelial cells.

A gluconeogenic strain of renal epithelial cells (LLC-PK1-F+) was used to characterize the effect of pH and bicarbonate concentration on the levels of phosphoenolpyruvate carboxykinase (PCK) and glutaminase (GA) mRNAs. The levels of both mRNAs are markedly dependent upon medium glucose concentration. The level of PCK mRNA is increased with increasing glucose concentration from 0 to 40 mM, whereas the level of GA mRNA is maximal between 3 and 5 mM glucose. When LLC-PK1-F+ cells are grown with 5 mM glucose and then subjected to an acute decrease in pH (from 7.4 to 6.9) and bicarbonate concentration (from 25 to 10 mM), the level of PCK mRNA exhibits a biphasic response. The PCK mRNA is initially increased 4-fold within 3 h, then decreases slightly and subsequently increases between 10 and 20 h to a level that is 17-fold greater than normal. Only the initial increase parallels the changes observed in vivo. In contrast, after onset of acidosis, the level of GA mRNA initially remains unchanged, is then increased 8-fold between 10 and 16 h, and then decreases slightly. This response closely mimics the results obtained in vivo. A decrease in media pH at constant bicarbonate causes a marked increase in both mRNAs. However, the levels of the two mRNAs are also elevated by decreasing bicarbonate at a constant pH. Thus, both parameters independently affect the level of the two mRNAs. The use of actinomycin D to measure the half-lives of PCK and GA mRNAs at pH 7.4 and 6.9 indicates that stabilization may fully account for the induction of GA mRNA and contributes to the inductive effects of decreased pH and/or bicarbonate on PCK mRNA. Following recovery from acidic conditions, the two mRNAs exhibit a rapid and coordinate decrease (t1/2 approximately 20 min). Dexamethasone had no effect on the level of either mRNA, whereas cAMP increased only PCK mRNA. The latter effect was additive with the increase caused by decreased pH and/or bicarbonate and was reversed by incubating in alkalotic media. Thus, the induction of PCK and GA mRNAs during acidosis is initiated in direct response to a decrease in extracellular pH and/or bicarbonate.     

Targeted disruption of the Myxococcus xanthus orotidine 5''-monophosphate decarboxylase gene: effects on growth and fruiting-body development.

The Myxococcus xanthus gene coding for orotidine 5'-monophosphate (OMP) decarboxylase (EC 4.1.1.23) was cloned. The M. xanthus uraA gene efficiently complemented an Escherichia coli OMP decarboxylase mutant, permitting it to grow in the absence of uracil. Electroporation of M. xanthus with a circular plasmid carrying a selectable uraA::kan gene disruption resulted in homologous recombination at the chromosomal uraA locus. Chromosomal integration of the gene disruption plasmid created heterozygous (uraA+/uraA::kan) tandem duplications. These tandem duplications were unstable and segregated auxotrophic uraA::kan daughters at frequencies of 2 x 10(-4) to 8 x 10(-4) per viable cell. Rare uraA::kan segregants were easily obtained by selecting for resistance to the toxic analog 5-fluoroorotic acid. Our experiments suggest that the cloned uraA gene could facilitate the use of gene duplications in the genetic analysis of M. xanthus development. The uraA mutants could utilize uracil, uridine, or uridine 5'-phosphate for growth, indicating that M. xanthus has pyrimidine salvage pathways. During multicellular development, uraA::kan gene disruption mutants sporulated to wild-type levels but formed smaller and more numerous aggregates than did their uraA+ parent, regardless of whether uracil was added to the medium. Pyrimidine deprivation of uraA mutants, under conditions that otherwise supported vegetative growth, failed to induce fruiting-body development or sporulation.     

The yeast SEC17 gene product is functionally equivalent to mammalian alpha-SNAP protein.

The SEC17 gene of Saccharomyces cerevisiae is required for vesicular transport between the endoplasmic reticulum and the Golgi apparatus. Here we report that the product of the SEC17 gene has the exact biochemical properties expected for a yeast homologue of the mammalian transport factor, alpha-SNAP. The DNA sequence of SEC17 codes for a protein of predicted molecular mass of 33 kDa. Immunoblotting indicates that Sec17p fractionates as a peripheral membrane protein and is mostly soluble when overexpressed, suggesting the presence of a saturable membrane receptor for Sec17p. Sec17p was purified from yeast cytosol using a SNAP-dependent in vitro mammalian Golgi transport assay. Kinetic analysis using this assay shows Sec17p acts temporally close to the fusion of transport vesicles with the medial Golgi compartment. In yeast extracts, Sec17p binds to Sec18p with a 1:1 stoichiometry. The interaction between Sec17p and Sec18p requires an activity provided by yeast membranes, and this putative membrane receptor activity is not extracted by high salt treatment of membranes.     

Activation of lignin and manganese peroxidase excretion in Phanerochaete chrysosporium by fungal extracts

Summary Lignin (LiP) and manganese peroxidase (MnP) excretion by Phanerochaete chrysosporium INA-12 was significantly increased in response to fungal extract supplementation. LiP and MnP production was increased 1.7- and 1.8-fold, respectively, with fungal extracts from agitated pellet cultures of strain INA-12, namely fungal extracts P₆ and P₄. In cultures supplemented with a fungal extract harvested from static cultures of strain INA-12 (fungal extract S₄), LiP and MnP production was increased 1.8- and 1.6-fold, respectively. Succinate dehydrogenase activity, a mitochondrial marker, was significantly enhanced (2.7-fold) in cultures with the addition of fungal extracts. Correspondence to: M. Asther     

Chronopharmacokinetics and Cardiovascular Effects of Nifedipine

Orcadian phase dependency in pharmacokinetics and hemodynamic effects on blood pressure and heart rate of different galenic formulations of nifedipine (immediate-release, sustained-release, and i.v. solution) were studied in healthy subjects or in hypertensive patients. Pharmacokinetics of immediate-release but not sustained-release and i.v. nifedipine were dependent on time of day: immediate-release nifedipine had higher C_max (peak concentration) and shorter t_max (time-to-peak concentration) after morning than evening application, and bioavailibility in the evening was reduced by about 40%. Orcadian rhythm in estimated hepatic blood flow as determined by indocyanine green kinetics may contribute to these chronokinetics. A circadian time dependency was also found in nifedipine-induced effects on blood pressure and heart rate as monitored by 24-h ambulatory blood pressure measurements. In conclusion, the dose response relationship of oral nifedipine is influenced by the circadian organization of the cardiovascular system as well as by the galenic drug formulation.     

Defects in fruiting body development caused by Tn5 lac insertions in Myxococcus xanthus.

Mutations caused by insertions of Tn5 lac that block development are rare. At least six of the eight mutations examined appeared to be regulatory. Three of these were found to disrupt social motility, suggesting a particular importance for this function. One other occurred in a known cell-cell interaction gene, bsgA, and the remaining two were located in genes operative early in the developmental program.