Genetic mapping of glutaric aciduria, type 3, to chromosome 7 and identification of mutations in c7orf10

While screening Old Order Amish children for glutaric aciduria type 1 (GA1) between 1989 and 1993, we found three healthy children who excreted abnormal quantities of glutaric acid but low 3-hydroxyglutaric acid, a pattern consistent with glutaric aciduria type 3 (GA3). None of these children had the GCDH c.1262C→T mutation that causes GA1 among the Amish. Using single-nucleotide polymorphism (SNP) genotypes, we identified a shared homozygous 4.7 Mb region on chromosome 7. This region contained 25 genes including C7orf10, an open reading frame with a putative mitochondrial targeting sequence and coenzyme-A transferase domain. Direct sequencing of C7orf10 revealed that the three Amish individuals were homozygous for a nonsynonymous sequence variant (c.895C→T, Arg299Trp). We then sequenced three non-Amish children with GA3 and discovered two nonsense mutations (c.322C→T, Arg108Ter, and c.424C→T, Arg142Ter) in addition to the Amish mutation. Two pathogenic alleles were identified in each of the six patients. There was no consistent clinical phenotype associated with GA3. In affected individuals, urine molar ratios of glutarate to its derivatives (3-hydroxyglutarate, glutarylcarnitine, and glutarylglycine) were elevated, suggesting impaired formation of glutaryl-CoA. These observations refine our understanding of the lysine-tryptophan degradation pathway and have important implications for the pathophysiology of GA1.     

Horizontal transmission of Symbiodinium cells between adult and juvenile corals is aided by benthic sediment

Of all reef-building coral species, 80–85 % initially draw their intracellular symbionts (dinoflagellates of the genus Symbiodinium) from the environment. Although Symbiodinium cells are crucial for the growth of corals and the formation of coral reefs, little is known about how corals first encounter free-living Symbiodinium cells. We report how the supply of free-living Symbiodinium cells to the benthos by adult corals can increase the rate of horizontal symbiont acquisition for conspecific recruits. Three species of newly settled aposymbiotic (i.e., symbiont-free) corals were maintained in an open aquarium system containing: sterilized sediment and adult coral fragments combined; adult coral fragments alone; sterilized sediment alone; or seawater at Heron Island, Great Barrier Reef, Australia. In all instances, the combination of an adult coral and sediment resulted in the highest symbiont acquisition rates by juvenile corals (up to five-fold greater than seawater alone). Juvenile corals exposed to individual treatments of adult coral or sediment produced an intermediate acquisition response (<52 % of recruits), and symbiont acquisition from unfiltered seawater was comparatively low (<20 % of recruits). Additionally, benthic free-living Symbiodinium cells reached their highest densities in the adult coral + sediment treatment (up to 1.2 × 10⁴ cells mL⁻¹). Our results suggest that corals seed microhabitats with free-living Symbiodinium cells suitable for many coral species during the process of coral recruitment.

     

Membrane targeting and pore formation by the type III secretion system translocon

The type III secretion system (T3SS) is a complex macromolecular machinery employed by a number of Gram-negative species to initiate infection. Toxins secreted through the system are synthesized in the bacterial cytoplasm and utilize the T3SS to pass through both bacterial membranes and the periplasm, thus being introduced directly into the eukaryotic cytoplasm. A key element of the T3SS of all bacterial pathogens is the translocon, which comprises a pore that is inserted into the membrane of the target cell, allowing toxin injection. Three macromolecular partners associate to form the translocon: two are hydrophobic and one is hydrophilic, and the latter also associates with the T3SS needle. In this review, we discuss recent advances on the biochemical and structural characterization of the proteins involved in translocon formation, as well as their participation in the modification of intracellular signalling pathways upon infection. Models of translocon assembly and regulation are also discussed.     

Metal binding dictates conformation and function of the amyloid precursor protein (APP) E2 domain

The amyloid precursor protein (APP) and its neurotoxic cleavage product Aβ are key players in the development of Alzheimer's disease and appear essential for neuronal development and cell homeostasis in mammals. Proteolytic processing of APP is influenced by metal ions, protein ligands and its oligomerization state. However, the structural basis and functional mechanism of APP regulation are hitherto largely unknown. Here we identified a metal-dependent molecular switch located within the E2 domain of APP containing four evolutionary highly conserved histidine residues. Three X-ray structures of the metal-bound molecule were solved at 2.6–2.0 Å resolution. Using protein crystallographic and biochemical methods, we characterized this novel high-affinity binding site within the E2 domain that binds competitively to copper and zinc at physiological concentrations. Metal-specific coordination spheres induce large conformational changes and enforce distinct structural states, most likely regulating the physiological function of APP and its processing in Alzheimer's disease.     

Lack of structure in the gene pool of the highly polyploid ornamental chrysanthemum

Selection of clonally propagated chrysanthemums is mostly performed on F1 hybrids using phenotypic characteristics without the use of molecular information. We applied 448 amplified fragment length polymorphism markers to a set of 81 accessions, mainly from the European gene pool, covering the different horticultural types (cut, pot and garden varieties) and originating from the most important European chrysanthemum breeders. The average pairwise genetic similarity of 0.69 was moderate to rather high. Neighbour-joining clustering resulted in no grouping of the accessions, either by their common origin or their horticultural type, or by similarities in important phenotypic characteristics. The structure of the dendrogram could not be supported by bootstrap analysis. Furthermore, network analysis using SplitsTree, principal coordinate analysis via DARwin or analysis of the population with structure did not differentiate reliable and invariable clusters. Therefore, we tested the marker saturation by plotting the mean coefficient of variation for every pairwise similarity of the bootstrap analysis against the different numbers of markers. We showed that the number of markers is sufficient for a precise estimate of genetic similarity and that the lack of bootstrap support is not due to a low genetic diversity or a lack of marker information, but most likely resulted from the breeding history of the cultivars, involving repeated backcrosses and the exchange of genotypes between breeders.     

Influence of group size on water imbibition by Hodotermes mossambicus alate termites

When newly emerged Hodotermes mossambicus alates are confined in pairs they drink almost half of their weight in water. Groups on the other hand do not exhibit this behaviour. The results obtained with individuals held in solitary confinement were intermediate between those obtained with pairs and groups. The imbibed water is stored in two large ‘water-sacs’ which extend well into the abdomen. Samples of the fluid from the ‘water-sacs’ had a relatively high freezing point and also contained far less Folin phenol positive material and Na⁺ and K⁺ than haemolymph.     

Nitrogen response efficiency of a managed and phytodiverse temperate grassland

Aims

Our goal was to assess how management and sward functional diversity affect nitrogen response efficiency (NRE), the ratio of plant biomass production to supply of available nitrogen (N) in temperate grassland.

Methods

A three-factorial design was employed: three sward compositions, two mowing frequencies, and two fertilization treatments.

Results

NRE was largely influenced by fertilization followed by mowing frequency and sward composition. NRE was larger in unfertilized than fertilized plots, in plots cut thrice than plots cut once per year, and in control swards than in monocot- or dicot-enhanced swards. Fertilization decreased NRE through decreases in both N uptake efficiency (plant N uptake per supply of available N) and N use efficiency (NUE, biomass produced per plant N uptake) whereas mowing frequency and sward composition affected NRE through N uptake efficiency rather than NUE. The largest NRE in the control sward with 70 % monocots and 30 % dicots attests that these proportions of functional groups were best adapted in this grassland ecosystem.

Conclusions

Optimum NRE may not be a target of most farmers, but it is an appropriate tool to evaluate the consequences of grassland management practices, which farmers may employ to maximize profit, on environmental quality.