A double coil chromatin sub-unit model.

A model is proposed for the structure of DNA in chromatin sub-units. Each sub-unit is proposed to contain two turns of an inner coil, with a pitch of about 40 A and an external diameter of 70 A. Around the inner coil is wound, in opposite handedness, a slightly larger amount of DNA at a diameter of about 150 A. The total contour length consistent with the electron micrographs and X-ray scattering is 600-700 A, or about 200 base pairs. It is suggested that the inner coil is protein rich and contains all of the histones except H1, which is associated with the outer coil. The double-coil model is consistent with previous biochemical and biophysical studies of chromatin. The existence of 200 and 100 base pair digestion fragments and a 6 to 1 DNA compaction are readily explained. This model is based upon the electron microscopic observation of replicas of frozen chromatin and X-ray and neutron scattering. Structural details of 25 A are preserved and visualized by the freeze electron microscopy techniques employed.     

Dung beetles as secondary seed dispersers in a temperate grassland

The two-phase dispersal event in which dung beetles move seeds after endozoochory is often assumed to be advantageous for plant regeneration. Because seeds are expected to end up in favourable and safe germination sites, it is considered as an example of directed dispersal. However, literature so far is restricted to tropical rain forest ecosystems, while data for temperate regions are lacking. In this study, the effect of dung beetles on seedling establishment of endozoochorically dispersed seeds is evaluated for a temperate grassland ecosystem. We performed a field experiment in which cages excluded dung beetles from horse and cattle dung samples with mixed-in grass seeds. Seed germination from these samples was significantly higher than that from samples which were accessible to dung beetles. This indicates that the effect of dung beetles on short-term seedling establishment was negative, which contrasts with the patterns found for large-seeded species used in tropical studies. This is most likely attributed to the lack of roller species and the larger depth at which tunneling Geotrupes species bury seeds.     

Left atrium remodeling predicts late recurrence of paroxysmal atrial fibrillation after second generation cryoballoon ablation

Background

Atrial fibrillation (AF) is the most common arrhythmia worldwide. Nowadays, AF ablation is a valuable treatment option. It has been shown that the left atrium (LA) diameter is a predictor of AF recurrence after cryoballoon ablation (CBA). Since it does not reflect the true LA size, we compared the role of different LA anatomical parameters using echocardiography for the prediction of AF recurrence after CBA.

Methods

We retrospectively included 209 patients (mean age 56.1?±?13.6 years, male 62%) with paroxysmal AF undergoing CBA. A transthoracic echocardiography was performed in all patients.

Results

At a mean follow-up of 16.9?±?6.3 months, AF recurred in 25.4% of the patients. LA anterior - posterior diameter (LAD), LA minimum volume (LAmin) and early AF recurrence were independent predictors of recurrence. Based on receiver operating characteristics, cut – off values for LAD and, LAmin were 41 mm, 23.69 mL, respectively. The negative predictive values for recurrence were 73% and 87.3% respectively. In patients with AF recurrence, a significant proportion (30.2%) showed LA longitudinal remodeling (LA superior – inferior diameter) even though classically measured LAD was normal.

Conclusions

Longitudinal LA remodeling plays an additional role for predicting AF recurrence after CBA, in patients without LAD dilation. Moreover, LAmin had a high negative predictive value and was an independent predictor of AF recurrence. Therefore, a more complete LA anatomical assessment allows a better prediction of AF recurrences after CBA.

     

Mass spectrometry imaging: How will it affect clinical research in the future?

Introduction: Mass spectrometry imaging (MSI) is a label free, multiplex imaging technology able to simultaneously record the distributions of 100’s to 1000’s of species, and which may be configured to study metabolites, lipids, glycans, peptides, and proteins simply by changing the tissue preparation protocol.

Areas covered: The capability of MSI to complement established histopathological practice through the identification of biomarkers for differential diagnosis, patient prognosis, and response to therapy; the capability of MSI to annotate tissues on the basis of each pixel’s mass spectral signature; the development of reproducible MSI through multicenter studies.

Expert commentary: We discuss how MSI can be combined with microsampling/microdissection technologies in order to investigate, with more depth of coverage, the molecular changes uncovered by MSI.     

The nuclear membrane integrity assay

A novel technique is described for the evaluation of membrane integrity in isolated nuclei. Membrane integrity is assessed by measuring nuclear fragility in response to high salt conditions. Salt-induced disruption of the nuclear membrane is followed by spectrophotometric monitoring of released nucleotides. The assay is based on determining the amount of salt necessary to induce release of 50% of the total pool of releasable nucleotides. This allows semiquantitative comparison of relative nuclear membrane strength or integrity of different samples in response to high salt conditions. In this manner, the effects of altered nuclear membrane composition or metabolism on membrane integrity may be monitored.