G Protein-Coupled Receptor Kinase 6 (GRK6) Regulates Insulin Processing and Secretion via Effects on Proinsulin Conversion to Insulin

Recent studies identified a missense mutation in the gene coding for G protein-coupled receptor kinase 6 (GRK6) that segregates with type 2 diabetes (T2D). To better understand how GRK6 might be involved in T2D, we used pharmacological inhibition and genetic knockdown in the mouse β-cell line, MIN6, to determine whether GRK6 regulates insulin dynamics. We show inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing while GRK6 knockdown revealed these same processing defects with reduced levels of cellular insulin. GRK6 knockdown cells also had attenuated insulin secretion but enhanced proinsulin secretion consistent with decreased processing. In support of these findings, we demonstrate GRK6 rescue experiments in knockdown cells restored insulin secretion after glucose treatment. The altered insulin profile appears to be caused by changes in the proprotein convertases, the enzymes responsible for proinsulin to insulin conversion, as GRK6 knockdown resulted in significantly reduced convertase expression and activity. To identify how the GRK6-P384S mutation found in T2D patients might affect insulin processing, we performed biochemical and cell biological assays to study the properties of the mutant. We found that while GRK6-P384S was more active than WT GRK6, it displayed a cytosolic distribution in cells compared to the normal plasma membrane localization of GRK6. Additionally, GRK6 overexpression in MIN6 cells enhanced proinsulin processing, while GRK6-P384S expression had little effect. Taken together, our data show that GRK6 regulates insulin processing and secretion in a glucose-dependent manner and provide a foundation for understanding the contribution of GRK6 to T2D

Spallation reactions. A successful interplay between modeling and applications

The spallation reactions are a type of nuclear reaction which occur in space by interaction of the cosmic rays with interstellar bodies. The first spallation reactions induced with an accelerator took place in 1947 at the Berkeley cyclotron (University of California) with 200 MeV deuterons and 400 MeV alpha beams. They highlighted the multiple emission of neutrons and charged particles and the production of a large number of residual nuclei far different from the target nuclei. The same year R. Serber describes the reaction in two steps: a first and fast one with high-energy particle emission leading to an excited remnant nucleus, and a second one, much slower, the de-excitation of the remnant. In 2010 IAEA organized a worskhop to present the results of the most widely used spallation codes within a benchmark of spallation models. If one of the goals was to understand the deficiencies, if any, in each code, one remarkable outcome points out the overall high-quality level of some models and so the great improvements achieved since Serber. Particle transport codes can then rely on such spallation models to treat the reactions between a light particle and an atomic nucleus with energies spanning from few tens of MeV up to some GeV. An overview of the spallation reactions modeling is presented in order to point out the incomparable contribution of models based on basic physics to numerous applications where such reactions occur. Validations or benchmarks, which are necessary steps in the improvement process, are also addressed, as well as the potential future domains of development. Spallation reactions modeling is a representative case of continuous studies aiming at understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie

The ectomycorrhizal fungal community in a neotropical forest dominated by the endemic dipterocarp Pakaraimaea dipterocarpacea.

Ectomycorrhizal (ECM) plants and fungi can be diverse and abundant in certain tropical ecosystems. For example, the primarily paleotropical ECM plant family Dipterocarpaceae is one of the most speciose and ecologically important tree families in Southeast Asia. Pakaraimaea dipterocarpacea is one of two species of dipterocarp known from the Neotropics, and is also the only known member of the monotypic Dipterocarpaceae subfamily Pakaraimoideae. This Guiana Shield endemic is only known from the sandstone highlands of Guyana and Venezuela. Despite its unique phylogenetic position and unusual geographical distribution, the ECM fungal associations of P. dipterocarpacea are understudied throughout the tree's range. In December 2010 we sampled ECM fungi on roots of P. dipterocarpacea and the co-occurring ECM tree Dicymbe jenmanii (Fabaceae subfamily Caesalpinioideae) in the Upper Mazaruni River Basin of Guyana. Based on ITS rDNA sequencing we documented 52 ECM species from 11 independent fungal lineages. Due to the phylogenetic distance between the two host tree species, we hypothesized that P. dipterocarpacea would harbor unique ECM fungi not found on the roots of D. jenmanii. Although statistical tests suggested that several ECM fungal species did exhibit host preferences for either P. dipterocarpacea or D. jenmanii, most of the ECM fungi were multi-host generalists. We also detected several ECM fungi that have never been found in long-term studies of nearby rainforests dominated by other Dicymbe species. One particular mushroom-forming fungus appears to be unique and may represent a new ECM lineage of Agaricales that is endemic to the Neotropics

Ectomycorrhizal fungi detected on the roots of <i>Pakaraimaea dipterocarpacea</i> and <i>Dicymbe jenmanii</i> in this study.

<p>Species-level operational taxonomic units (OTUs) are defined as sequences that are ≥97% similar across the ITS rDNA sequence region. Taxa labeled with Latin binomials or voucher numbers (TH, MCA) were identified based on ITS matches with sporocarps. Species with ECM numbers are known only from sequences obtained from ECM roots. All species are assigned to the ECM lineages defined in Tedersoo et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055160#pone.0055160-Tedersoo4" target="_blank">[36]</a>. The numbers shown in the columns labeled <i>Pakaraimaea dipterocarpacea</i> and <i>Dicymbe jenmanii</i> designate the number of occurrences of each fungal OTU per host species. In cases where a particular fungal OTU was detected on more than one root tip from an individual tree this was not counted as a separate occurrence. The column on the far right indicates whether or not an OTU has been found previously on ECM roots or as sporocarps at other sites in Guyana.</p

Frequency of occurrence of the 17 most common ectomycorrhizal (ECM) fungi on the roots of host trees <i>Pakaraimaea dipterocarpacea</i> (white bars) and <i>Dicymbe jenmanii</i> (black bars) at the Pegaima savanna site, Upper Mazaruni Basin, Guyana.

<p>Each of these common fungal species occurred on three or more individual trees; 20 trees were sampled for each of the host tree species. Species that showed a significantly different distribution on the two host plants (as assessed by Fischer’s Exact test) are indicated by asterisks. Fungal species that have never been found in previous ECM sporocarp or root surveys in nearby rainforest sites are designated by black circles. All other ECM fungal species have been found previously in association with species of <i>Dicymbe</i> and <i>Aldina</i> at other locations. Named fungal species are indicated by a genus and species binomial whereas species with TH or MCA numbers were matched to voucher specimens of undescribed species identified to genus. The ECM numbers correspond to fungal species known only from ECM root sequences.</p

Affinities of Agaricales TH9235 based on BlastN analysis of three gene regions (18S rDNA, 28S rDNA, mtLSU).

<p>BlastN results based on ITS rDNA are not shown because they are uninformative (see text). In addition to the number of shared nucleotides and the percent similarity shared between Agaricales TH9235 and each of the top BLAST hits, the trophic mode and spore color of each species is also shown.</p