Arabidopsis CURVATURE THYLAKOID1 Proteins Modify Thylakoid Architecture by Inducing Membrane Curvature

Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme curvature at margins is generated and maintained. We report the identification of the CURVATURE THYLAKOID1 (CURT1) protein family, conserved in plants and cyanobacteria. The four Arabidopsis thaliana CURT1 proteins (CURT1A, B, C, and D) oligomerize and are highly enriched at grana margins. Grana architecture is correlated with the CURT1 protein level, ranging from flat lobe-like thylakoids with considerably fewer grana margins in plants without CURT1 proteins to an increased number of membrane layers (and margins) in grana at the expense of grana diameter in overexpressors of CURT1A. The endogenous CURT1 protein in the cyanobacterium Synechocystis sp PCC6803 can be partially replaced by its Arabidopsis counterpart, indicating that the function of CURT1 proteins is evolutionary conserved. In vitro, Arabidopsis CURT1A proteins oligomerize and induce tubulation of liposomes, implying that CURT1 proteins suffice to induce membrane curvature. We therefore propose that CURT1 proteins modify thylakoid architecture by inducing membrane curvature at grana margins.     

Individual tooth macrowear pattern guides the reconstruction of Sts 52 (Australopithecus africanus) dental arches

The functional restoration of the occlusal relationship between maxillary and mandibular tooth rows is a major challenge in modern dentistry and maxillofacial surgery. Similar technical challenges are present in paleoanthropology when considering fragmented and deformed mandibular and maxillary fossils. Sts 52, an Australopithecus africanus specimen from Sterkfontein Member 4, represents a typical case where the original shape of the dental arches is no longer preserved. It includes a partial lower face (Sts 52a) and a fragmented mandible (Sts 52b), both incomplete and damaged to such an extent to thwart attempts at matching upper and lower dentitions. We show how the preserved macrowear pattern of the tooth crowns can be used to functionally reconstruct Sts 52's dental arches. High‐resolutiondental stone casts of Sts 52 maxillary and mandibular dentition were mounted and repositioned in a dental articulator. The occlusal relationship between antagonists was restored based on the analysis of the occlusal wear pattern of each preserved tooth, considering all dental contact movements represented in the occlusal compass. The reconstructed dental arches were three‐dimensional surface scanned and their occlusal kinematics tested in a simulation. The outcome of this contribution is the first functional restoration of A. africanus dental arches providing new morphometric data for specimen Sts 52. It is noteworthy that the method described in this case study might be applied to several other fossilspecimens. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

207-nm UV Light - A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. I: In Vitro Studies

Background

0.5% to 10% of clean surgeries result in surgical-site infections, and attempts to reduce this rate have had limited success. Germicidal UV lamps, with a broad wavelength spectrum from 200 to 400 nm are an effective bactericidal option against drug-resistant and drug-sensitive bacteria, but represent a health hazard to patient and staff. By contrast, because of its limited penetration, ∼200 nm far-UVC light is predicted to be effective in killing bacteria, but without the human health hazards to skin and eyes associated with conventional germicidal UV exposure.

Aims

The aim of this work was to test the biophysically-based hypothesis that ∼200 nm UV light is significantly cytotoxic to bacteria, but minimally cytotoxic or mutagenic to human cells either isolated or within tissues.

Methods

A Kr-Br excimer lamp was used, which produces 207-nm UV light, with a filter to remove higher-wavelength components. Comparisons were made with results from a conventional broad spectrum 254-nm UV germicidal lamp. First, cell inactivation vs. UV fluence data were generated for methicillin-resistant S. aureus (MRSA) bacteria and also for normal human fibroblasts. Second, yields of the main UV-associated pre-mutagenic DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts) were measured, for both UV radiations incident on 3-D human skin tissue.

Results

We found that 207-nm UV light kills MRSA efficiently but, unlike conventional germicidal UV lamps, produces little cell killing in human cells. In a 3-D human skin model, 207-nm UV light produced almost no pre-mutagenic UV-associated DNA lesions, in contrast to significant yields induced by a conventional germicidal UV lamp.

Conclusions

As predicted based on biophysical considerations, 207-nm light kills bacteria efficiently but does not appear to be significantly cytotoxic or mutagenic to human cells. Used appropriately, 207-nm light may have the potential for safely and inexpensively reducing surgical-site infection rates, including those of drug-resistant origin.     

FLT3 Mutations in Early T-Cell Precursor ALL Characterize a Stem Cell Like Leukemia and Imply the Clinical Use of Tyrosine Kinase Inhibitors

Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) has been identified as high-risk subgroup of acute T-lymphoblastic leukemia (T-ALL) with a high rate of FLT3-mutations in adults. To unravel the underlying pathomechanisms and the clinical course we assessed molecular alterations and clinical characteristics in a large cohort of ETP-ALL (n = 68) in comparison to non-ETP T-ALL adult patients. Interestingly, we found a high rate of FLT3-mutations in ETP-ALL samples (n = 24, 35%). Furthermore, FLT3 mutated ETP-ALL was characterized by a specific immunophenotype (CD2+/CD5-/CD13+/CD33-), a distinct gene expression pattern (aberrant expression of IGFBP7, WT1, GATA3) and mutational status (absence of NOTCH1 mutations and a low frequency, 21%, of clonal TCR rearrangements). The observed low GATA3 expression and high WT1 expression in combination with lack of NOTCH1 mutations and a low rate of TCR rearrangements point to a leukemic transformation at the pluripotent prothymocyte stage in FLT3 mutated ETP-ALL. The clinical outcome in ETP-ALL patients was poor, but encouraging in those patients with allogeneic stem cell transplantation (3-year OS: 74%). To further explore the efficacy of targeted therapies, we demonstrate that T-ALL cell lines transfected with FLT3 expression constructs were particularly sensitive to tyrosine kinase inhibitors. In conclusion, FLT3 mutated ETP-ALL defines a molecular distinct stem cell like leukemic subtype. These data warrant clinical studies with the implementation of FLT3 inhibitors in addition to early allogeneic stem cell transplantation for this high risk subgroup.     

Forward Modeling of Fluctuating Dietary 13C Signals to Validate 13C Turnover Models of Milk and Milk Components from a Diet-Switch Experiment

Isotopic variation of food stuffs propagates through trophic systems. But, this variation is dampened in each trophic step, due to buffering effects of metabolic and storage pools. Thus, understanding of isotopic variation in trophic systems requires knowledge of isotopic turnover. In animals, turnover is usually quantified in diet-switch experiments in controlled conditions. Such experiments usually involve changes in diet chemical composition, which may affect turnover. Furthermore, it is uncertain if diet-switch based turnover models are applicable under conditions with randomly fluctuating dietary input signals. Here, we investigate if turnover information derived from diet-switch experiments with dairy cows can predict the isotopic composition of metabolic products (milk, milk components and feces) under natural fluctuations of dietary isotope and chemical composition. First, a diet-switch from a C₃-grass/maize diet to a pure C₃-grass diet was used to quantify carbon turnover in whole milk, lactose, casein, milk fat and feces. Data were analyzed with a compartmental mixed effects model, which allowed for multiple pools and intra-population variability, and included a delay between feed ingestion and first tracer appearance in outputs. The delay for milk components and whole milk was ∼12 h, and that of feces ∼20 h. The half-life (t_½) for carbon in the feces was 9 h, while lactose, casein and milk fat had a t_½ of 10, 18 and 19 h. The ¹³C kinetics of whole milk revealed two pools, a fast pool with a t_½ of 10 h (likely representing lactose), and a slower pool with a t_½ of 21 h (likely including casein and milk fat). The diet-switch based turnover information provided a precise prediction (RMSE ∼0.2 ‰) of the natural ¹³C fluctuations in outputs during a 30 days-long period when cows ingested a pure C3 grass with naturally fluctuating isotope composition.     

Complete Mitochondrial DNA Sequences of the Threadfin Cichlid (Petrochromis trewavasae) and the Blunthead Cichlid (Tropheus moorii) and Patterns of Mitochondrial Genome Evolution in Cichlid Fishes

The cichlid fishes of the East African Great Lakes represent a model especially suited to study adaptive radiation and speciation. With several African cichlid genome projects being in progress, a promising set of closely related genomes is emerging, which is expected to serve as a valuable data base to solve questions on genotype-phenotype relations. The mitochondrial (mt) genomes presented here are the first results of the assembly and annotation process for two closely related but eco-morphologically highly distinct Lake Tanganyika cichlids, Petrochromis trewavasae and Tropheus moorii. The genomic sequences comprise 16,588 bp (P. trewavasae) and 16,590 bp (T. moorii), and exhibit the typical mitochondrial structure, with 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a non-coding control region. Analyses confirmed that the two species are very closely related with an overall sequence similarity of 96%. We analyzed the newly generated sequences in the phylogenetic context of 21 published labroid fish mitochondrial genomes. Consistent with other vertebrates, the D-loop region was found to evolve faster than protein-coding genes, which in turn are followed by the rRNAs; the tRNAs vary greatly in the rate of sequence evolution, but on average evolve the slowest. Within the group of coding genes, ND6 evolves most rapidly. Codon usage is similar among examined cichlid tribes and labroid families; although a slight shift in usage patterns down the gene tree could be observed. Despite having a clearly different nucleotide composition, ND6 showed a similar codon usage. C-terminal ends of Cox1 exhibit variations, where the varying number of amino acids is related to the structure of the obtained phylogenetic tree. This variation may be of functional relevance for Cox1 synthesis.