Spatial and temporal expression of histone demethylase,Kdm2a,during murine molar development

The histone demethylase, lysine (K)-specific demethylase 2A (Kdm2a), is highly conserved and expressed ubiquitously. Kdm2a can regulate cell proliferation and osteo/dentinogenic, adipogenic and chondrogenic differentiation of mesenchymal stem cells (MSCs) derived from dental tissue. We used quantitative real-time RT-PCR analysis and immunohistochemistry to detect Kdm2a expression during development of the murine molar at embryonic days E12, E14, E16 and E17 and postnatal days P3 and P14. Immunohistochemistry results showed no positive staining of Kdm2a at E12. At E14, Kdm2a was expressed weakly in the inner enamel epithelium, stellate reticulum cells and dental sac. At E16, Kdm2a was expressed mainly in the inner and outer enamel epithelium, stratum intermedium and dental sac, but weaker staining was found in cervical loop and dental papilla cells adjacent to the basement membrane. At E17, the strongest Kdm2a staining was detected in the ameloblasts and stronger Kdm2a staining also was detected in the stratum intermedium, outer enamel epithelium and dental papilla cells compared to the expression at E16. Postnatally, we found that Kdm2a was localized in secretory and mature ameloblasts and odontoblasts, and dentin was unstained. Real-time RT-PCR showed that Kdm2a mRNA levels in murine germ cells increased from E12 to E14 and from E14 to E16; no significant change occurred at E16, E17 or P3, then the levels decreased at P14 compared to P3. Kdm2a expression may be closely related to cell proliferation, to ameloblast and odontoblast differentiation and to the secretion of extracellular enamel and dentin during murine tooth development.     

Building retinal connectomes

Understanding vertebrate vision depends on knowing, in part, the complete network graph of at least one representative retina. Acquiring such graphs is the business of synaptic connectomics, emerging as a practical technology due to improvements in electron imaging platform control, management software for large-scale datasets, and availability of data storage. The optimal strategy for building complete connectomes uses transmission electron imaging with 2nm or better resolution, molecular tags for cell identification, open-access data volumes for navigation, and annotation with open-source tools to build 3D cell libraries, complete network diagrams and connectivity databases. The first forays into retinal connectomics have shown that even nominally well-studied cells have much richer connection graphs than expected.     

Natural selection affects multiple aspects of genetic variation at putatively neutral sites across the human genome

A major question in evolutionary biology is how natural selection has shaped patterns of genetic variation across the human genome. Previous work has documented a reduction in genetic diversity in regions of the genome with low recombination rates. However, it is unclear whether other summaries of genetic variation, like allele frequencies, are also correlated with recombination rate and whether these correlations can be explained solely by negative selection against deleterious mutations or whether positive selection acting on favorable alleles is also required. Here we attempt to address these questions by analyzing three different genome-wide resequencing datasets from European individuals. We document several significant correlations between different genomic features. In particular, we find that average minor allele frequency and diversity are reduced in regions of low recombination and that human diversity, human-chimp divergence, and average minor allele frequency are reduced near genes. Population genetic simulations show that either positive natural selection acting on favorable mutations or negative natural selection acting against deleterious mutations can explain these correlations. However, models with strong positive selection on nonsynonymous mutations and little negative selection predict a stronger negative correlation between neutral diversity and nonsynonymous divergence than observed in the actual data, supporting the importance of negative, rather than positive, selection throughout the genome. Further, we show that the widespread presence of weakly deleterious alleles, rather than a small number of strongly positively selected mutations, is responsible for the correlation between neutral genetic diversity and recombination rate. This work suggests that natural selection has affected multiple aspects of linked neutral variation throughout the human genome and that positive selection is not required to explain these observations.     

Ancient DNA identifies post‐glacial recolonisation,not recent bottlenecks,as the primary driver of contemporary mtDNA phylogeography and diversity in Scandinavian brown bears

Aim

Brown bear populations in Scandinavia show a strong mitochondrial DNA (mtDNA) phylogeographic structure and low diversity relative to other parts of Europe. Identifying the timing and origins of this mtDNA structure is important for conservation programs aimed at restoring populations to a natural state. Therefore, it is essential to identify whether contemporary genetic structure is linked to post‐glacial recolonisation from divergent source populations or an artefact of demographic impacts during recent population bottlenecks. We employed ancient DNA techniques to investigate the timing and potential causes of these patterns.

Location

Scandinavia and Europe.

Methods

Ancient mtDNA sequences from 20 post‐glacial Scandinavian bears were used to investigate phylogeographic structure and genetic diversity over the last 6000 years. MtDNA from 19 Holocene Norwegian bears was compared with 499 sequences from proximate extant populations in Sweden, Finland, Estonia and western Russia. A single mtDNA sequence from a Holocene Denmark sample was compared with 149 ancient and modern bears from Western Europe.

Results

All nineteen Holocene Norwegian samples are identical to or closely related to the most common mtDNA haplotype found in northern Europe today. MtDNA diversity was low and not significantly different from extant populations in northern Europe. In Denmark, we identified a single mtDNA haplotype that is previously unrecorded from Scandinavia.

Main conclusions

The current discrete phylogeographic structure and lack of mtDNA diversity in Scandinavia is attributed to serial founder effects during post‐glacial recolonisation from divergent source populations rather than an artefact of recent anthropogenic impacts. In contrast to previous interpretations, the recolonisation of southern Scandinavia may not have been limited to bears from a single glacial refugium. Results highlight the importance of conserving the long‐term evolutionary separation between northern and southern populations and identify southern Scandinavia as an important reservoir of mtDNA diversity that is under threat in other parts of Europe.

     

The Effect of Cataract on Early Stage Glaucoma Detection Using Spatial and Temporal Contrast Sensitivity Tests

Background

To investigate the effect of cataract on the ability of spatial and temporal contrast sensitivity tests used to detect early glaucoma.

Methods

Twenty-seven glaucoma subjects with early cataract (mean age 60 ±10.2 years) which constituted the test group were recruited together with twenty-seven controls (cataract only) matched for age and cataract type from a primary eye care setting. Contrast sensitivity to flickering gratings at 20 Hz and stationary gratings with and without glare, were measured for 0.5, 1.5 and 3 cycles per degree (cpd) in central vision. Perimetry and structural measurements with the Heidelberg Retinal Tomograph (HRT) were also performed.

Results

After considering the effect of cataract, contrast sensitivity to stationary gratings was reduced in the test group compared with controls with a statistically significant mean difference of 0.2 log units independent of spatial frequency. The flicker test showed a significant difference between test and control group at 1.5 and 3 cpd (p = 0.019 and p = 0.011 respectively). The percentage of glaucoma patients who could not see the temporal modulation was much higher compared with their cataract only counterparts. A significant correlation was found between the reduction of contrast sensitivity caused by glare and the Glaucoma Probability Score (GPS) as measured with the HRT (p<0.005).

Conclusions

These findings indicate that both spatial and temporal contrast sensitivity tests are suitable for distinguishing between vision loss as a consequence of glaucoma and vision loss caused by cataract only. The correlation between glare factor and GPS suggests that there may be an increase in intraocular stray light in glaucoma.     

Inflammatory markers CD11b, CD16, CD66b, CD68, myeloperoxidase and neutrophil elastase in eccentric exercised human skeletal muscles

The aim of the present study was to investigate leucocyte markers, CD11b, CD16, CD66b, CD68, myeloperoxidase and neutrophil elastase on skeletal muscle biopsies from biceps brachii after unaccustomed eccentric exercise followed by the second bout of exercise 3 weeks later. The subjects (10 subjects received COX-2 inhibitor (Celecoxib) and 13 subjects received placebo) were divided into three categories: mild, moderate and severe effect of eccentric exercise, according to the reduction and recovery of muscle force-generating capacity after performing 70 maximal eccentric actions with elbow flexors on an isokinetic dynamometer. The results showed that the CD66b antibody was applicable for localization of neutrophils in human skeletal muscle, whereas the other studied neutrophil markers recognized also other leucocytes than neutrophils. The number of CD66b positive cells in skeletal muscle was very low and was not affected by the exercise. The macrophage marker CD68 showed reactivity also against satellite cells and fibroblast-like cells in skeletal muscle and therefore cannot be applied as a quantitative value for inflammatory cells. Skeletal muscle fibre injury, shown as dystrophin negative fibres, was observed approximately in half of the biopsies at 4 and 7 days after the first exercise bout in the categories moderate and severe effect of eccentric exercise. These subjects represent the most prominent loss in muscle force-generating capacity both at the category and the individual levels. Furthermore, deformed skeletal muscle fibres were observed in five subjects in these categories after the second bout of exercise. The present results suggest that neutrophils are not involved in skeletal muscle fibre injury and the reduction in muscle force-generating capacity after a single bout of eccentric exercise is a good indirect indicator of muscle damage in humans. Furthermore, prolonged regeneration process could be one of the reasons for impaired peripheral muscle function after high-force eccentric exercise.