Cloning of the nupC gene of Escherichia coli encoding a nucleoside transport system, and identification of an adjacent Insertion element, IS 186

Escherichia coli is known to contain more than one active transport system for nucleoside uptake. In the present study we report the sequence of a gene encoding a second nucleoside transport system, nupC (in addition to nupG.) An open reading frame (ORF) of 1200bp was identified that codes for a hydrophobic polypeptide of 43 560 Da and an NupC fusion protein was shown to be membrane associated. The native NupC protein is also identified, following over-expression. NupC exhibits short regions of homology to several membrane-associated proteins, including LacY and Cyd. Analysis of the nupC promoter region revealed the presence of at least two putative CRP-binding sites, centred at–40bp and–89bp, which probably flank a CytR-binding site. In addition, an adjacent IS186 element was identified and found to reside within a putative terminator structure, downstream from the nupC ORF. This arrangement is shown to reflect the previously established gene order on the E. coli chromosome.     

The effect of methyl palmoxirate on incorporation of [U-14C]palmitate into rat brain

We examined the dose response, time course and reversibility of the effect of methyl 2-tetradecylglycidate (McN-3716, methyl palmoxirate or MEP), an inhibitor of -oxidation of fatty acids, on incorporation of radiolabeled palmitic acid ([U-¹⁴C]PA) from plasma into brain lipids of awake rats. MEP (0.1, 1 and 10 mg/kg) or vehicle was administered intravenously from 10 min to 72 hr prior to infusion of [U-¹⁴C]PA. Two hr pretreatment with MEP (0.1 to 10 mg/kg) increased brain organic radioactivity 1.2 to 1.8 fold and decreased brain aqueous radioactivity by 1.2 to 3.0 fold when compared to control values. At 10 mg/kg, MEP significantly increased brain organic fraction from 40% in controls to 85%, 30 min to 6 hr pretreatment, and resulted in a redistribution of the radiolabeled fatty acid toward triacylglycerol. MEP changed the lipid/aqueous brain ratio of incorporated [U-¹⁴C]PA from 0.67 to 5.7. The incorporation rate coefficient, k^*, was significantly increased by MEP (10 mg/kg) at 2 hr (31%), 4 hr (59%) and 6 hr (34%). All effects were reversed by 72 hr, consistent with a half-life of 2 days for carnitine palmitoyl transferase I. These results indicate that intravenous MEP may be used with [1-¹¹C]palmitic acid for studying brain lipid metabolism in vivo by positron emission tomography, as it significantly reduces the large unincorporated aqueous fraction that would result in high background radioactivity.     

The TRH neuronal phenotype forms embryonic cell clusters that go on to establish a regionalized cell fate in forebrain

How neurons diversify in developing brain to produce discrete cell fates in their appropriate regions remains a fundamental question. Embryonic Xenopus was previously used to identify juxtaposed embryonic cells that first express proopiomelanocortin mRNA in forebrain and pituitary, supporting the idea that this neuropeptide phenotype is induced locally. (Hayes and Loh, 1990, Development 110:747–757). To begin to examine how a more widespread population of forebrain cells is set up, the present focus is on the thyrotropin-releasing hormone (TRH) phenotype. Serial section in situ hybridization histochemistry produced the unexpected finding that the adult-like TRH system spanning forebrain and comprising over six different telencephalic and diencephalic nuclei, is preceded by an embryonic TRH cell population that is initially localized and then highly regionalized in the area from which the adult pattern develops. Thus, the first TRH cells, detected in vivo after 35 h (stage 29/30), were confined to discrete anterior or posterior bilateral clusters in embryonic forebrain or hindbrain. Thereafter, the TRH cell clusters in diencephelon, but not hindbrain, expanded to form rows, extending anteriorly into telencephalon and bifurcating posteriorly around the infundibulum. By 80 h (stage 42), after extensive brain morphogenesis, these forebrain rows showed regional differences in levels of TRH and mRNA corresponding to the specific brain nuclei that have been shown to contain TRH cells in adult. These findings show that subsets of phenotype-specific forebrain cell first form a regionalized neuronal cell fate before distinct brain nuclei form. This is turn points to the testable hypothesis in Xenopus that certain neuronal cell fates in forebrain may be dictated by cell lineage or local induction. 1994 John Wiley & Sons, Inc.     

Effects of Motility and Adsorption Rate Coefficient on Transport of Bacteria through Saturated Porous Media

Three strains of Pseudomonas fluorescens with different motility rates and adsorption rate coefficients were injected into porous-medium reactors packed with l-mm-diameter glass spheres. Cell breakthrough, time to peak concentration, tailing, and cell recovery were measured at three interstitial pore velocities (higher than, lower than, and much lower than the maximal bacterial motility rate). All experiments were done with distilled water to reduce the effects of growth and chemotaxis. Contrary to expectations, motility did not result in either early breakthrough or early time to peak concentration at flow velocities below the motility rate. Bacterial size exclusion effects were shown to affect breakthrough curve shape at the very low flow velocity, but no such effect was seen at the higher flow velocity. The tendency of bacteria to adsorb to porous-medium surfaces, as measured by adsorption rate coefficients, profoundly influenced transport characteristics. Cell recoveries were shown to be correlated with the ratio of advective to adsorptive transport in the reactors. Adsorption rate coefficients were found to be better predictors of microbial transport phenomena than individual characteristics, such as size, motility, or porous-medium hydrodynamics.     

Atrial natriuretic peptide binding in rat placenta,yolk sac,decidua, and materal placental vessels

Using in vitro autoradiography, binding sites of ¹²⁵I-ANP (atrial natriuretic peptide) were localized in the rat placenta, visceral yolk sac, and decidua at 16, 18, and 20 days of gestation. There was diffuse binding over the labyrinthine region of the placenta and an intense binding over the decidual gland and visceral yolk sac. In the yolk sac, ANP localized over the cores of the villi where it may be involved with the regulation of transport across the membranes or the flow of blood through the vitelline vessels. Of particular interest was binding over the maternal blood vessels supplying the decidual region and placenta. Receptors were located on the endothelial cells and smooth muscle cells of the arteries and veins, indicating that ANP may be involved with regional regulation of blood flow to the placenta.