Environmental fluctuations promote intraspecific diversity and population persistence via inflationary effects

The impact of temporal variation in the environment, specifically the amount of temporal autocorrelation, on population processes is of growing interest in ecology and evolutionary biology. It was recently discovered that temporal autocorrelation in the environment can significantly increase the abundance of populations that would otherwise have low, or even negative long‐term growth rates (via so‐called ‘inflationary effects’), provided that immigration from another source prevents extinction. Here we use a mathematical model to ask whether inflationary effects can also increase population persistence without immigration if different phenotypes within that population partition growth over time and buffer each other from extinction via mutation. Using a combination of analytical and numerical methods, we find that environmental autocorrelation can inflate the abundance of phenotypes that would otherwise be excluded from the population, provided that phenotypes are sufficiently different in their use of the environment. This inflation of abundance at the phenotypic level also generates an inflation of abundance at the population level. Remarkably, intraspecific inflationary effects can increase both phenotypic and whole population abundance even if one or all phenotypes are maladapted to the environment, as long as mutations prevent phenotypic extinction during periods of poor environmental conditions. Given the prevalence of temporally autocorrelated environmental variables in nature, intraspecific inflationary effects have the potential to be of widespread importance for population persistence as well as the maintenance of intraspecific diversity.     

Reg-2 is a motoneuron neurotrophic factor and a signalling intermediate in the CNTF survival pathway

Cytokines that are related to ciliary neurotrophic factor (CNTF) are physiologically important survival factors for motoneurons, but the mechanisms by which they prevent neuronal cell death remain unknown. Reg-2/PAP I (pancreatitis-associated protein I), referred to here as Reg-2, is a secreted protein whose expression in motoneurons during development is dependent on cytokines. Here we show that CNTF-related cytokines induce Reg-2 expression in cultured motoneurons. Purified Reg-2 can itself act as an autocrine/paracrine neurotrophic factor for a subpopulation of motoneurons, by stimulating a survival pathway involving phosphatidylinositol-3-kinase, Akt kinase and NF-kappaB. Blocking Reg-2 expression in motoneurons using Reg-2 antisense adenovirus specifically abrogates the survival effect of CNTF on cultured motoneurons, indicating that Reg-2 expression is a necessary step in the CNTF survival pathway. Reg-2 shows a unique pattern of expression in late embryonic spinal cord: it is progressively upregulated in individual motoneurons on a cell-by-cell basis, indicating that only a fraction of motoneurons in a given motor pool may be exposed to cytokines. Thus, Reg-2 is a neurotrophic factor for motoneurons, and is itself an obligatory intermediate in the survival signalling pathway of CNTF-related cytokines.     

Effect of osmotic, alkaline, acid or thermal stresses on the growth and inhibition of Listeria monocytogenes

Five strains of Listeria monocytogenes (a, b, c, d and e) isolated from industrial plants have been subjected to different osmotic, alkaline, acid or thermal stresses. The effects of these treatments on lag-phase (L) and growth rate (mu) of cells in mid-log phase have been followed using an automated optical density monitoring system. Increasing the osmotic pressure by the addition of different amounts of NaCl increased the lag phase and decreased the growth rate. The same phenomena were observed after decreasing the pH of the medium to 5.8, 5.6 or 5.4 by addition of acetic, lactic or hydrochloric acids. The inhibitory effect was: acetic acid > lactic acid > hydrochloric acid. The addition of NaOH to attain pH values of 9.5, 10.0, 10.5 or 11.0 in the medium produced a dramatic increase of the lag phase at pH 10.5 and 11. Growth rates were also decreased while the maximal population increased with high pH values. These effects varied according to strains. Strains d and e were the most resistant to acidic and alkaline stresses, and e was the most affected by the addition of NaCl. A cold shock of 30 min at 0 degree C had limited effects on growth parameters. On the other hand, hyperthermal shocks (55 or 63 degrees C, 30 min) led to similar increased lag phases and to significant increases of the maximal population in all five strains.     

Nitrogen uptake by heterotrophic bacteria and phytoplankton in Arctic surface waters

We estimated rates of heterotrophic bacterial and phytoplanktonuptake of nitrate, ammonium, and urea using ¹⁵N-labelled nitrogenand specific metabolic inhibitors of prokaryote and eukaryotenitrogen metabolism in the surface waters of the North Water(northern Baffin Bay) during autumn that were characterizedby the absence of cyanobacteria (comprising prochlorophytes).The percentage of nitrate + ammonium uptake by heterotrophicbacteria ranged between 44 and 78% of the measured total uptakeand was the highest when the phytoplankton biomass was relativelylow (<2 µg Chlorophyll a L^–1). Phytoplanktonaccounted for a larger fraction (e.g., 58–95%) of ureauptake than heterotrophic bacteria. When our results are combinedwith those from previous studies carried out in diverse temperateand polar areas, it appears that heterotrophic bacteria accountfor 25% (14–40%; median and interquartile range) of thetotal nitrate uptake in surface waters with chlorophyll biomass<2 µg L^–1. Estimates of new production computedfrom phytoplankton carbon uptake and f-ratios may be stronglyoverestimated in regions where nitrate uptake by heterotrophicbacteria is high and the biomass of phytoplankton is low.     

High-yield production of short GpppA- and 7MeGpppA-capped RNAs and HPLC-monitoring of methyltransfer reactions at the guanine-N7 and adenosine-2′O positions

Many eukaryotic and viral mRNAs, in which the first transcribed nucleotide is an adenosine, are decorated with a cap-1 structure, ^7MeG^5′-ppp^5′-A_2′OMe. The positive-sense RNA genomes of flaviviruses (Dengue, West Nile virus) for example show strict conservation of the adenosine. We set out to produce GpppA- and ^7MeGpppA-capped RNA oligonucleotides for non-radioactive mRNA cap methyltransferase assays and, in perspective, for studies of enzyme specificity in relation to substrate length as well as for co-crystallization studies. This study reports the use of a bacteriophage T7 DNA primase fragment to synthesize GpppAC_n and ^7MeGpppAC_n (1≤n≤9) in a one-step enzymatic reaction, followed by direct on-line cleaning HPLC purification. Optimization studies show that yields could be modulated by DNA template, enzyme and substrate concentration adjustments and longer reaction times. Large-scale synthesis rendered pure (in average 99%) products (1≤n≤7) in quantities of up to 100nmol starting from 200nmol cap analog. The capped RNA oligonucleotides were efficient substrates of Dengue virus (nucleoside-2′-O-)-methyltransferase, and human (guanine-N7)-methyltransferase. Methyltransfer reactions were monitored by a non-radioactive, quantitative HPLC assay. Additionally, the produced capped RNAs may serve in biochemical, inhibition and structural studies involving a variety of eukaryotic and viral methyltransferases and guanylyltransferases.     

A Calcium Homeostasis Mechanism Induced by Heterologous Expression of Total RNA from Chicory Leaves in Xenopus Oocytes

Xenopus oocytes were injected with total RNA from chicory leaf tissues and then examined by the voltage-clamp technique. A double-step voltage protocol was used, with an initial hyperpolarization step from the holding potential of −35 to −140 mV followed by a second depolarization step to +60 mV. Two different outward currents were observed, one noninactivating (I _ni ), and one inactivating (I _i ). Only the noninactivating outward current (I _ni ) could be induced by depolarization from −35 to +60 mV. The mean amplitude of I _ni was 2915 ± 848 nA (n= 11). This current, carried by chloride ions, declined nearly to the baseline in 153 ± 64 sec (n= 13), and was highly dependent on intracellular calcium. After the rundown of I _ni , the same oocyte was depolarized from −140 to +60 mV. This protocol induced an inactivating outward current (I _i ) with a mean amplitude of 4461 ± 1605 nA (n= 13). I _i was also carried by chloride ions and dependent on extracellular calcium. I _i was strongly inhibited by 100 μm extracellular La³⁺. These two types of chloride currents were also observed after IP₃ injection in control oocytes. I _ni and I _i were not observed in noninjected oocytes or water-injected oocytes. We suggest that the expression of total chicory leaf tissue RNA in Xenopus oocytes reveals a calcium homeostasis mechanism responsible for calcium mobilization from internal stores and subsequent calcium entry. Received: 22 May 1998/Revised: 2 October 1998     

One-pot synthesis of antiviral acyclovir and other nucleosides derivatives using doped natural phosphate as lewis acid catalyst

Natural phosphate doped with iodine or potassium iodide is an active catalyst for the one-pot synthesis of acyclonucleosides. To demonstrate the utility of the new catalyst system, the highly important antiviral drug acyclovir was directly and regioselectively obtained from NAcG with no byproducts.     

Folate-conjugated iron oxide nanoparticles for solid tumor targeting as potential specific magnetic hyperthermia mediators: synthesis, physicochemical characterization, and in vitro experiments

New folate-conjugated superparamagnetic maghemite nanoparticles have been synthesized for the intracellular hyperthermia treatment of solid tumors. These ultradispersed nanosystems have been characterized for their physicochemical properties and tumor cell targeting ability, facilitated by surface modification with folic acid. Preliminary experiments of nanoparticles heating under the influence of an alternating magnetic field at 108 kHz have been also performed. The nanoparticle size, surface charge, and colloidal stability have been assessed in various conditions of ionic strength and pH. The ability of these folate "decorated" maghemite nanoparticles to recognize the folate receptor has been investigated both by surface plasmon resonance and in folate receptor expressing cell lines, using radiolabeled folic acid in competitive binding experiments. The specificity of nanoparticle cellular uptake has been further investigated by transmission electron microscopy after incubation of these nanoparticles in the presence of three cell lines with differing folate receptor expression levels. Qualitative and quantitative determinations of both folate nanoparticles and nontargeted control nanoparticles demonstrated a specific cell internalization of the folate superparamagnetic nanoparticles.     

1H-NMR Assignments of the Non-exchangeable Protons of the Consensus Donor Exon:Intron Junction d(CpApGpGpTpApApGpT)

Abstract

The consensus donor exon:intron junction d(CpApGpGpTpApApGpT) has been synthesized by a modified phosphotriester method. The non-self-complementary nonamer has, in principle, only two G,C or four A,T points of self-recognition. The inference that it exists in the single strand form at 20°C was confirmed by temperature variable ¹H-NMR and NOE measurements. The proton assignments were secured using two-dimensional COSY which provided intra-nucleotide correlations, then NOE difference measurements as well as inversion recovery T₁ experiments. Systematic procedures were developed for the assignment of the individual bases and their component protons based on the effects of molecular environment on chemical shifts. These latter procedures should be useful for the assignment of other random-coil single strand oligodeoxyribonucleotides.