Redox-induced structural dynamics of Fe-heme ligand in myoglobin by X-ray absorption spectroscopy

The Fe(III) --> Fe(II) reduction of the heme iron in aquomet-myoglobin, induced by x-rays at cryogenics temperatures, produces a thermally trapped nonequilibrium state in which a water molecule is still bound to the iron. Water dissociates at T > 160 K, when the protein can relax toward its new equilibrium, deoxy form. Synchrotron radiation x-ray absorption spectroscopy provides information on both the redox state and the Fe-heme structure. Owing to the development of a novel method to analyze the low-energy region of x-ray absorption spectroscopy, we obtain structural pictures of this photo-inducible, irreversible process, with 0.02-0.06-A accuracy, on the protein in solution as well as in crystal. After photo-reduction, the iron-proximal histidine bond is shortened by 0.15 A, a reinforcement that should destabilize the iron in-plane position favoring water dissociation. Moreover, we are able to get the distance of the water molecule even after dissociation from the iron, with a 0.16-A statistical error.     

The efficacy of performing field surveys during the dry and rainy seasons to estimate species richness and composition of local bat assemblages

Here we assessed the efficacy of performing field surveys during both dry and rainy seasons to estimate species richness and composition of phyllostomid bats in 12 sites of the Brazilian Atlantic Forest. Our goal was to elucidate two opposite scenarios. If bat species compositions differ between the dry and rainy seasons, then field surveys in both seasons will be considered complementary for estimating local bat assemblages. In contrast, if bat species compositions in the dry season are a nested subset of the species present in the rainy season, then field surveys in both seasons will be considered redundant. Our results showed that field surveys performed only during the rainy season exhibited the same efficacy in recording bat species as field surveys considering both dry and rainy seasons combined. Consequently, the rare species sampled in the rainy season contributed to the uniqueness of communities in terms of species composition. Considering that time, funding, and the number of field personnel available for work are important factors when determining the sampling effort in highly biodiverse regions like the tropics, our results can be useful in establishing protocols for research projects with limited resources aiming to create a comprehensive list of species.     

Increasing winter temperatures explain body size decrease in wintering bird populations of Northern Europe—But response patterns vary along the spatioclimatic gradient

Aim

Recent evidence has shown changes in body size and shape of individuals, which are suggested to be a result of global warming caused by climate change. Here, we explored the spatiotemporal changes in wing length and body mass of 24 wintering bird species in Northern Europe and how these relate to temperature anomaly.

Location

Finland and Sweden, Europe.

Time Period

50 years, 1970 to 2020.

Major Taxa Studied

Birds, 24 species.

Methods

We used site-specific, long-term winter ringing data containing wing length and body mass measurements from across Sweden and Finland for 24 bird species. We modelled wing length and body mass change over time, in relation to the spatioclimatic gradient and as response to temperature anomalies (of [i] the same winter as the ringing took place, [ii] the previous winter and [iii] the previous spring) by accounting for phylogenetic relatedness between species and their species-specific responses to each predictor of interest.

Results

We show that across all species, body size has decreased since the 1970s, with a negative relationship between wing length and temperature anomalies of previous winters, suggesting carry-over effects likely linked to body size-related survival or dispersal. Body mass was negatively related to the temperature anomaly of the same winter, indicating more immediate effects related to reduced fat reserves during mild winters.

Main Conclusions

Our results highlight a climate-driven decrease in body size across several species and its association with positive anomalies in winter temperature in the high latitudes. However, the responses are not spatially uniform and there is considerable species-specific variation, emphasizing the importance of conducting multispecies studies when investigating responses to climate change. The mechanisms of decreasing wing length and body mass seem to differ and underline the immediate and carry-over effects of temperature warming during the nonbreeding season.     

The behaviour of nuclear domains in the course of apoptosis

Programmed cell death is activated, by different stimuli and in many cell types, to regulate cell population balance during tissue proliferation and embryogenesis. Its initial event seems to be, in most cases, the activation of a Ca²⁺-dependent endonuclease, causing DNA cleavage into nucleosomic fragments. Its morphological expression is characterized by deep nuclear changes, consisting of typical cap-shaped chromatin marginations, followed by nuclear fragmentation and final formation of numerous micronuclei. Cytoplasmic damage appears in a very late stage of the process and the greatest part of the phenomenon appears to take place despite good preservation of the plasma membrane and organellar component. In the present study we analyzed apoptosis in camptothecin-treated HL60 leukaemia cells, and in freshly isolated mouse thymocytes treated with dexamethasone. The process was first quantified and time monitored by flow cytometry. Subsequently the specimens were processed for morphological examination in order to investigate the behaviour of the different nuclear domains. To follow DNA and RNA localization, we utilized osmium ammine and DNase-colloidal gold cytochemical reactions. The concentration of most DNA in the cap-shaped structures was demonstrated by these reactions. Confocal microscopy of cells processed by in situ nick-translation suggested that DNA was firstly cleaved and subsequently condensed in cup-shaped structures. Despite the strong nuclear modifications, nucleoli could be clearly recognized until the late apoptotic stages.     

Real-time imaging of the dynamics of secretory granules in growth cones

Secretory granules containing a hybrid protein consisting of the regulated secretory protein tissue plasminogen activator and an enhanced form of green fluorescent protein were tracked at high spatial resolution in growth cones of differentiated PC12 cells. Tracking shows that granules, unlike synaptic vesicles, generally are mobile in growth cones. Quantitative analysis of trajectories generated by granules revealed two dominant modes of motion: diffusive and directed. Diffusive motion was observed primarily in central and peripheral parts of growth cones, where most granules diffused two to four orders of magnitude more slowly than comparably sized spheres in dilute solution. Directed motion was observed primarily in proximal parts of growth cones, where a subset of granules underwent rapid, directed motion at average speeds comparable to those observed for granules in neurites. This high-resolution view of the dynamics of secretory granules in growth cones provides insight into granule organization and release at nerve terminals. In particular, the mobility of granules suggests that granules, unlike synaptic vesicles, are not tethered stably to cytoskeletal structures in nerve terminals. Moreover, the slow diffusive nature of this mobility suggests that secretory responses involving centrally distributed granules in growth cones will occur slowly, on a time scale of minutes or longer.