Linkage Analysis Reveals the Independent Origin of Poeciliid Sex Chromosomes and a Case of Atypical Sex Inheritance in the Guppy (Poecilia reticulata)

Among different teleost fish species, diverse sex-determining mechanisms exist, including environmental and genetic sex determination, yet chromosomal sex determination with male heterogamety (XY) prevails. Different pairs of autosomes have evolved as sex chromosomes among species in the same genus without evidence for a master sex-determining locus being identical. Models for evolution of Y chromosomes predict that male-advantageous genes become linked to a sex-determining locus and suppressed recombination ensures their co-inheritance. In the guppy, Poecilia reticulata, a set of genes responsible for adult male ornaments are linked to the sex-determining locus on the incipient Y chromosome. We have identified >60 sex-linked molecular markers to generate a detailed map for the sex linkage group of the guppy and compared it with the syntenic autosome 12 of medaka. We mapped the sex-determining locus to the distal end of the sex chromosome. We report a sex-biased distribution of recombination events in female and male meiosis on sex chromosomes. In one mapping cross, we observed sex ratio and male phenotype deviations and propose an atypical mode of genetic sex inheritance as its basis.     

Modified micro suction cup/rhizobox approach for the in-situ detection of organic acids in rhizosphere soil solution

Root–soil interactions can strongly influence the soil solution chemistry in the rhizosphere. In the present study we propose a modification of the classical rhizobox/micro suction cup system to make it suitable for the collection and analysis of organic acids in the rhizosphere. In order to show the potential of the method, we tested the modified system with Lupinus albus L. as a model plant known to exude large amounts of citrate. The suction cups were installed through the transparent front plate of the rhizoboxes just after the emergence of cluster roots in order to allow optimal localized collection of soil solution. A small dead-volume allowed almost immediate stabilisation with formaldehyde of the sampled soil solutions in the collection container to prevent microbial degradation. The concentrations of organic acids were significantly larger in the rhizosphere soil solution of active cluster roots of Lupinus albus L. than in the bulk soil solution (about 400 μM of citrate versus <0.05 μM). We were able to follow the exudation process in-situ, which occurred during 2–3 days. Also the concentrations of other organic acids and inorganic anions differed between the bulk soil and the rhizosphere of cluster roots, normal roots, and nodules.     

Mutation in a "tesB-like" hydroxyacyl-coenzyme A-specific thioesterase gene causes hyperproduction of extracellular polyhydroxyalkanoates by Alcanivorax borkumensis SK2

A novel mutant of the marine oil-degrading bacterium Alcanivorax borkumensis SK2, containing a mini-Tn5 transposon disrupting a "tesB-like" acyl-coenzyme A (CoA) thioesterase gene, was found to hyperproduce polyhydroxyalkanoates (PHA), resulting in the extracellular deposition of this biotechnologically important polymer when grown on alkanes. The tesB-like gene encodes a distinct novel enzyme activity, which acts exclusively on hydroxylated acyl-CoAs and thus represents a hydroxyacyl-CoA-specific thioesterase. Inactivation of this enzyme results in the rechanneling of CoA-activated hydroxylated fatty acids, the cellular intermediates of alkane degradation, towards PHA production. These findings may open up new avenues for the development of simplified biotechnological processes for the production of PHA as a raw material for the production of bioplastics.     

ProBDNF collapses neurite outgrowth of primary neurons by activating RhoA

Background

Neurons extend their dendrites and axons to build functional neural circuits, which are regulated by both positive and negative signals during development. Brain-derived neurotrophic factor (BDNF) is a positive regulator for neurite outgrowth and neuronal survival but the functions of its precursor (proBDNF) are less characterized.

Methodology/Principal Findings

Here we show that proBDNF collapses neurite outgrowth in murine dorsal root ganglion (DRG) neurons and cortical neurons by activating RhoA via the p75 neurotrophin receptor (p75NTR). We demonstrated that the receptor proteins for proBDNF, p75NTR and sortilin, were highly expressed in cultured DRG or cortical neurons. ProBDNF caused a dramatic neurite collapse in a dose-dependent manner and this effect was about 500 fold more potent than myelin-associated glycoprotein. Neutralization of endogenous proBDNF by using antibodies enhanced neurite outgrowth in vitro and in vivo, but this effect was lost in p75NTR^−/− mice. The neurite outgrowth of cortical neurons from p75NTR deficient (p75NTR^−/−) mice was insensitive to proBDNF. There was a time-dependent reduction of length and number of filopodia in response to proBDNF which was accompanied with a polarized RhoA activation in growth cones. Moreover, proBDNF treatment of cortical neurons resulted in a time-dependent activation of RhoA but not Cdc42 and the effect was absent in p75NTR^−/− neurons. Rho kinase (ROCK) and the collapsin response mediator protein-2 (CRMP-2) were also involved in the proBDNF action.

Conclusions

proBDNF has an opposing role in neurite outgrowth to that of mature BDNF. Our observations suggest that proBDNF collapses neurites outgrowth and filopodial growth cones by activating RhoA through the p75NTR signaling pathway.     

Adrenergic Stimulation of Cyclic GMP Formation Requires NO-Dependent Activation of Cytosolic Guanylate Cyclase in Rat Pinealocytes

Abstract: Cyclic GMP (cGMP) formation in rat pinealocytes is regulated through a synergistic dual receptor mechanism involving β-and α₁-adrenergic receptors. The effects of N -monomethyl- l -arginine (NMMA), which inhibits nitric oxide (NO) synthase and NO-mediated activation of cytosolic guanylate cyclase, and methylene blue (MB), which inhibits cytosolic guanylate cyclase, were investigated in an attempt to understand the role of NO in adrenergic cGMP formation. Both NMMA and MB inhibited β-adrenergic stimulation of cGMP formation as well as α₁-adrenergic potentiation of β-adrenergic stimulation of cGMP formation, whereas they had no effect in unstimulated pinealocytes. The inhibitory action of NMMA was antagonized by addition of l -arginine. On the basis of these findings it can be concluded that the adrenergic stimulation of cGMP formation involves NO synthesis followed by activation of cytosolic guanylate cyclase.