Premature chromosome condensation in humans associated with microcephaly and mental retardation: a novel autosomal recessive condition

We report a novel autosomal recessive disorder characterized by premature chromosome condensation in the early G2 phase. It was observed in two siblings, from consanguineous parents, affected with microcephaly, growth retardation, and severe mental retardation. Chromosome analysis showed a high frequency of prophase-like cells (>10%) in lymphocytes, fibroblasts, and lymphoblast cell lines with an otherwise normal karyotype. (3)H-thymidine-pulse labeling and autoradiography showed that, 2 h after the pulse, 28%-35% of the prophases were labeled, compared with 9%-11% in healthy control subjects, indicating that the phenomenon is due to premature chromosome condensation. Flow cytometry studies demonstrate that the entire cell cycle is not prolonged, compared with that in healthy control subjects, and compartment sizes did not differ from those in healthy control subjects. No increased reaction of the cells to X-irradiation or treatments with the clastogens bleomycin and mitomycin C was observed, in contrast to results in the cell-cycle mutants ataxia telangiectasia and Fanconi anemia. The rates of sister chromatid exchanges and the mitotic nondisjunction rates were inconspicuous. Premature entry of cells into mitosis suggests that a gene involved in cell-cycle regulation is mutated in these siblings.     

Mutations in autism susceptibility candidate 2 (AUTS2) in patients with mental retardation

We report on three unrelated mentally disabled patients, each carrying a de novo balanced translocation that truncates the autism susceptibility candidate 2 (AUTS2) gene at 7q11.2. One of our patients shows relatively mild mental retardation; the other two display more profound disorders. One patient is also physically disabled, exhibiting urogenital and limb malformations in addition to severe mental retardation. The function of AUTS2 is presently unknown, but it has been shown to be disrupted in monozygotic twins with autism and mental retardation, both carrying a translocation t(7;20)(q11.2;p11.2) (de la Barra et al. in Rev Chil Pediatr 57:549–554, 1986; Sultana et al. in Genomics 80:129–134, 2002). Given the overlap of this autism/mental retardation (MR) phenotype and the MR-associated disorders in our patients, together with the fact that mapping of the additional autosomal breakpoints involved did not disclose obvious candidate disease genes, we ascertain with this study that AUTS2 mutations are clearly linked to autosomal dominant mental retardation.     

Characterization of recombinant amino-terminal NC4 domain of human collagen IX: interaction with glycosaminoglycans and cartilage oligomeric matrix protein

The N-terminal NC4 domain of collagen IX is a globular structure projecting away from the surface of the cartilage collagen fibril. Several interactions have been suggested for this domain, reflecting its location and its characteristic high isoelectric point. In an attempt to characterize the NC4 domain in more detail, we set up a prokaryotic expression system to produce the domain. The purified 27.5-kDa product was analyzed for its glycosaminoglycan-binding potential by surface plasmon resonance and solid-state assays. The results show that the NC4 domain of collagen IX specifically binds heparin with a K(d) of 0.6 microm, and the full-length recombinant collagen IX has an even stronger interaction with heparin, with an apparent K(d) of 3.6 nm. The heparin-binding site of the NC4 domain was located in the extreme N terminus, containing a heparin-binding consensus sequence, whereas electron microscopy suggested the presence of at least three additional heparin-binding sites on full-length collagen IX. The NC4 domain was also shown to bind cartilage oligomeric matrix protein. This interaction and the association of cartilage oligomeric matrix protein with other regions of collagen IX were found to be heparin-competitive. Circular dichroism analyses of the NC4 domain indicated the presence of stabilizing disulfide bonds and a thermal denaturation point of about 80 degrees C. The pattern of disulfide bond formation within the NC4 domain was identified by tryptic peptide mass mapping of the NC4 in native and reduced states. A similar pattern was demonstrated for the NC4 domain of full-length recombinant collagen IX.     

Effects of forest conversion into grassland on soil aggregate structure and carbon storage in Panama: evidence from soil carbon fractionation and stable isotopes

Land-use and land-cover strongly influence soil properties such as the amount of soil organic carbon (SOC), aggregate structure and SOC turnover processes. We studied the effects of a vegetation shift from forest to grassland 90 years ago in soils derived from andesite material on Barro Colorado Island (BCI), Panama. We quantified the amount of carbon (C) and nitrogen (N) and determined the turnover of C in bulk soil, water stable aggregates (WSA) of different size classes (<53 μm, 53–250 μm, 250–2000 μm and 2000–8000 μm) and density fractions (free light fraction, intra-aggregate particulate organic matter and mineral associated soil organic C). Total SOC stocks (0–50 cm) under forest (84 Mg C ha⁻¹) and grassland (64 Mg C ha⁻¹) did not differ significantly. Our results revealed that vegetation type did not have an effect on aggregate structure and stability. The investigated soils at BCI did not show higher C and N concentrations in larger aggregates, indicating that organic material is not the major binding agent in these soils to form aggregates. Based on δ¹³C values and treating bulk soil as a single, homogenous C pool we estimated a mean residence time (MRT) of 69 years for the surface layer (0–5 cm). The MRT varied among the different SOC fractions and among depth. In 0–5 cm, MRT of intra-aggregate particulate organic matter (iPOM) was 29 years; whereas mineral associated soil organic C (mSOC) had a MRT of 124 years. These soils have substantial resilience to C and N losses because the >90% of C and N is associated with mSOC, which has a comparatively long MRT.     

Discovery and Structure Activity Relationship of Small Molecule Inhibitors of Toxic β-Amyloid-42 Fibril Formation

Increasing evidence implicates Aβ peptides self-assembly and fibril formation as crucial events in the pathogenesis of Alzheimer disease. Thus, inhibiting Aβ aggregation, among others, has emerged as a potential therapeutic intervention for this disorder. Herein, we employed 3-aminopyrazole as a key fragment in our design of non-dye compounds capable of interacting with Aβ42 via a donor-acceptor-donor hydrogen bond pattern complementary to that of the β-sheet conformation of Aβ42. The initial design of the compounds was based on connecting two 3-aminopyrazole moieties via a linker to identify suitable scaffold molecules. Additional aryl substitutions on the two 3-aminopyrazole moieties were also explored to enhance π-π stacking/hydrophobic interactions with amino acids of Aβ42. The efficacy of these compounds on inhibiting Aβ fibril formation and toxicity in vitro was assessed using a combination of biophysical techniques and viability assays. Using structure activity relationship data from the in vitro assays, we identified compounds capable of preventing pathological self-assembly of Aβ42 leading to decreased cell toxicity.     

Soil water uptake by trees using water stable isotopes (δ2H and δ18O)−a method test regarding soil moisture,texture and carbonate

Aims

Stable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition.

Methods

In the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry.

Results

The isotopic composition of extracted soil water was similarly depleted in both ¹⁸O and ²H with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the δ¹⁸O composition while δ²H was not affected.

Conclusions

Our results indicate that soil carbonate can cause artifacts for ¹⁸O isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for δ¹⁸O and δ²H in plant water uptake studies.     

Rainfall partitioning into throughfall and stemflow and associated nutrient fluxes: land use impacts in a lower montane tropical region of Panama

Land-use change alters catchment hydrology by influencing the quality and quantity of partitioned rainfall. We compared rainfall partitioning (throughfall, stemflow and interception) and nutrient concentrations in rainfall, throughfall and stemflow in three land-use types [primary forest (PF), secondary forest (SF) and agriculture (A)] in Panama. Measurements of throughfall were highly variable which may have masked seasonal and land use differences but it was clear that throughfall at agricultural sites made up a larger proportion of gross precipitation than at forest sites. Of incident precipitation, 94% became throughfall in agriculture sites while 83 and 81% of gross precipitation became throughfall in PF and SF, respectively. The size of the precipitation event was the main driver of variation in throughfall and stemflow. Consistent patterns in nutrient cycling were also difficult to identify. Vegetation has a vital role in delivering nutrients as throughfall deposition of K was often larger than precipitation deposition. A canopy budget model indicated that canopy exchange was often more dominant than dry deposition. Throughfall was generally enriched with nutrients, especially K and Mg, with enrichment factors of up to 17 and 5 for K and Mg, respectively, in PF. In contrast, Ca was sometimes taken up by the canopy. Values of nutrient deposition were high (with up to 15, 3, 30 and 15 kg ha^?1 month^?1 in stand deposition of Ca, Mg, K and Na, respectively in PF), possibly due to the slash-and-burn agricultural practices in the area or marine inputs. Throughfall and stemflow are vital sources of nutrients in these ecosystems.     

Monomeric Amyloid Beta Peptide in Hexafluoroisopropanol Detected by Small Angle Neutron Scattering

Small proteins like amyloid beta (Aβ) monomers are related to neurodegenerative disorders by aggregation to insoluble fibrils. Small angle neutron scattering (SANS) is a nondestructive method to observe the aggregation process in solution. We show that SANS is able to resolve monomers of small molecular weight like Aβ for aggregation studies. We examine Aβ monomers after prolonged storing in d-hexafluoroisopropanol (dHFIP) by using SANS and dynamic light scattering (DLS). We determined the radius of gyration from SANS as 1.0±0.1 nm for Aβ_1–40 and 1.6±0.1 nm for Aβ_1–42 in agreement with 3D NMR structures in similar solvents suggesting a solvent surface layer with 5% increased density. After initial dissolution in dHFIP Aβ aggregates sediment with a major component of pure monomers showing a hydrodynamic radius of 1.8±0.3 nm for Aβ_1–40 and 3.2±0.4 nm for Aβ_1–42 including a surface layer of dHFIP solvent molecules.     

Molecular interactions between prions as seeds and recombinant prion proteins as substrates resemble the biological interspecies barrier in vitro

Prion diseases like Creutzfeldt-Jakob disease in humans, Scrapie in sheep or bovine spongiform encephalopathy are fatal neurodegenerative diseases, which can be of sporadic, genetic, or infectious origin. Prion diseases are transmissible between different species, however, with a variable species barrier. The key event of prion amplification is the conversion of the cellular isoform of the prion protein (PrP(C)) into the pathogenic isoform (PrP(Sc)). We developed a sodiumdodecylsulfate-based PrP conversion system that induces amyloid fibril formation from soluble α-helical structured recombinant PrP (recPrP). This approach was extended applying pre-purified PrP(Sc) as seeds which accelerate fibrillization of recPrP. In the present study we investigated the interspecies coherence of prion disease. Therefore we used PrP(Sc) from different species like Syrian hamster, cattle, mouse and sheep and seeded fibrillization of recPrP from the same or other species to mimic in vitro the natural species barrier. We could show that the in vitro system of seeded fibrillization is in accordance with what is known from the naturally occurring species barriers.