Digest: Untangling the influence of soft and hard selection in experimental populations—from environment to genomics*

Gallet et al. (2018) studied the effect of two selection regimes on the maintenance of polymorphism in experimental populations. They took two strains of Escherichia coli, each resistant to a different antibiotic, evolved them in culture conditions representing “soft” or “hard” selective regimes, and measured polymorphism levels for three to five transfers. Their results supported theoretical predictions that only “soft” selection maintains polymorphism, highlighting the importance of experimental studies to understand maintenance of variation in nature.     

Complement C3 Drives Autophagy-Dependent Restriction of Cyto-invasive Bacteria

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Bayesian Nonparametric Estimation of the Probability of Discovering New Species

We consider the problem of evaluating the probability of discoveringa certain number of new species in a new sample of populationunits, conditional on the number of species recorded in a basicsample. We use a Bayesian nonparametric approach. The differentspecies proportions are assumed to be random and the observationsfrom the population exchangeable. We provide a Bayesian estimator,under quadratic loss, for the probability of discovering newspecies which can be compared with well-known frequentist estimators.The results we obtain are illustrated through a numerical exampleand an application to a genomic dataset concerning the discoveryof new genes by sequencing additional single-read sequencesof cdna fragments.     

An essential saccharide binding domain for the mAb 2C7 established for Neisseria gonorrhoeae LOS by ES-MS and MSn

A study of bacterial surface oligosaccharides were investigated among different strains of Neisseria gonorrhoeae to correlate structural features essential for binding to the MAb 2C7. This epitope is widely expressed and conserved in gonococcal isolates, characteristics essential to an effective candidate vaccine antigen. Sample lipooligosaccharides (LOS), was prepared by a modification of the hot phenol-water method from which de-O-acetylated LOS and oligosaccharide (OS) components were analyzed by ES-MS-CID-MS and ES-MSnin a triple quadrupole and an ion trap mass spectrometer, respectively. Previously documented natural heterogeneity was apparent from both LOS and OS preparations which was admixed with fragments induced by hydrazine and mild acid treatment. Natural heterogeneity was limited to phosphorylation and antenni extensions to the alpha-chain. Mild acid hydrolysis to release OS also hydrolyzed the beta(1-->6) glycosidic linkage of lipid A. OS structures were determined by collisional and resonance excitation combined with MS and multistep MSn which provided sequence information from both neutral loss, and nonreducing terminal fragments. A comparison of OS structures, with earlier knowledge of MAb binding, enzyme treatment, and partial acid hydrolysis indicates a generic overlapping domain for 2C7 binding. Reoccurring structural features include a Hepalpha(1-->3)Hepbeta(1-->5)KDO trisaccharide core branched on the nonreducing terminus (Hep-2) with an alpha(1-->2) linked GlcNAc (gamma-chain), and an alpha-linked lactose (beta-chain) residue. From the central heptose (Hep-1), a beta(1-->4) linked lactose (alpha-chain), moiety is required although extensions to this residue appear unnecessary.      

Signaling pathways of kaempferol-3-neohesperidoside in glycogen synthesis in rat soleus muscle

Kaempferol 3-neohesperidoside is one of the several compounds that have been reported to have insulin-like properties in terms of glucose lowering. We studied the effect of kaempferol 3-neohesperidoside in glycogen synthesis in rat soleus muscle through the incorporation of ¹⁴C-d-glucose in glycogen. Kaempferol 3-neohesperidoside stimulates glycogen synthesis in rat soleus muscle by approximately 2.38-fold. Insulin at 100 nM showed a stimulatory effect on glycogen synthesis when compared with the control group. The stimulatory effect of kaempferol 3-neophesperidoside on glycogen synthesis was inhibited by wortmannin, the phosphatidylinositol 3-kinase (PI3K) inhibitor, and enhanced by lithium chloride, a glycogen synthase kinase 3 (GSK-3) inhibitor. Moreover, the stimulatory effect of kaempferol 3-neohesperidoside was also nullified by PD98059, a specific inhibitor of mitogen-activated protein kinase (MEK) and by calyculin A, an inhibitor of protein phosphatase 1 (PP1) activity. It was concluded that the PI3K – GSK-3 pathway and MAPK – PP1 pathway are involved in the stimulatory kaempferol 3-neohesperidoside effect on glycogen synthesis in rat soleus muscle.     

Rapid stimulatory effect of thyroxine on plasma membrane transport systems: Calcium uptake and neutral amino acid accumulation in immature rat testis

Although the biological effects of thyroid hormones are mediated by nuclear receptors (genomic mechanisms), interactions with receptors associated with the plasma membrane (non-genomic mechanisms) of target cells are not clear. In this study we investigated the rapid stimulatory effect of thyroxine (T₄) on ⁴⁵Ca²⁺ uptake as well as ionic currents and intracellular messengers involved in the stimulatory action of T₄ in amino acid accumulation in immature rat testes. Results indicated that 10^?9 M or 10^?6 M T₄ was able to increase immediately ⁴⁵Ca²⁺ uptake after 60 s of hormone exposure. These results indicate for the first time that voltage-dependent Ca²⁺ channels and ATP-dependent K⁺ channels can be seen as a set-point in the stimulatory effect of T₄ on amino acid accumulation. Apamin-sensitive small-conductance Ca²⁺-activated K⁺ channels (SK_Ca) and chloride channels were shown to be partially involved in this mechanism. The amino acid accumulation triggered by the PKC pathway suggests a functional link between different ion channel activities and the stimulatory effect of T₄ on amino acid accumulation. In conclusion, we show in this study a rapid and stimulatory effect of T₄ on calcium uptake and on amino acid accumulation, both events initiated at the plasma membrane, which strongly characterizes a non-genomic effect of T₄ in immature rat testes.