Social sleepers: The effects of social status on sleep in terrestrial mammals.

Social status among group-living mammals can impact access to resources, such as water, food, social support, and mating opportunities, and this differential access to resources can have fitness consequences. Here, we propose that an animal's social status impacts their access to sleep opportunities, as social status may predict when an animal sleeps, where they sleep, who they sleep with, and how well they sleep. Our review of terrestrial mammals examines how sleep architecture and intensity may be impacted by (1) sleeping conditions and (2) the social experience during wakefulness. Sleeping positions vary in thermoregulatory properties, protection from predators, and exposure to parasites. Thus, if dominant individuals have priority of access to sleeping positions, they may benefit from higher quality sleeping conditions and, in turn, better sleep. With respect to waking experiences, we discuss the impacts of stress on sleep, as it has been established that specific social statuses can be characterized by stress-related physiological profiles. While much research has focused on how dominance hierarchies impact access to resources like food and mating opportunities, differential access to sleep opportunities among mammals has been largely ignored despite its potential fitness consequences.

Spontaneous reversal of the developmental aging of normal human cells following transcriptional reprogramming.

AIM: To determine whether transcriptional reprogramming is capable of reversing the developmental aging of normal human somatic cells to an embryonic state. MATERIALS & METHODS: An isogenic system was utilized to facilitate an accurate assessment of the reprogramming of telomere restriction fragment (TRF) length of aged differentiated cells to that of the human embryonic stem (hES) cell line from which they were originally derived. An hES-derived mortal clonal cell strain EN13 was reprogrammed by SOX2, OCT4 and KLF4. The six resulting induced pluripotent stem (iPS) cell lines were surveyed for telomere length, telomerase activity and telomere-related gene expression. In addition, we measured all these parameters in widely-used hES and iPS cell lines and compared the results to those obtained in the six new isogenic iPS cell lines. RESULTS: We observed variable but relatively long TRF lengths in three widely studied hES cell lines (16.09-21.1 kb) but markedly shorter TRF lengths (6.4-12.6 kb) in five similarly widely studied iPS cell lines. Transcriptome analysis comparing these hES and iPS cell lines showed modest variation in a small subset of genes implicated in telomere length regulation. However, iPS cell lines consistently showed reduced levels of telomerase activity compared with hES cell lines. In order to verify these results in an isogenic background, we generated six iPS cell clones from the hES-derived cell line EN13. These iPS cell clones showed initial telomere lengths comparable to the parental EN13 cells, had telomerase activity, expressed embryonic stem cell markers and had a telomere-related transcriptome similar to hES cells. Subsequent culture of five out of six lines generally showed telomere shortening to lengths similar to that observed in the widely distributed iPS lines. However, the clone EH3, with relatively high levels of telomerase activity, progressively increased TRF length over 60 days of serial culture back to that of the parental hES cell line. CONCLUSION: Prematurely aged (shortened) telomeres appears to be a common feature of iPS cells created by current pluripotency protocols. However, the spontaneous appearance of lines that express sufficient telomerase activity to extend telomere length may allow the reversal of developmental aging in human cells for use in regenerative medicine.

Influence of nanoparticle size on the pH-dependent structure of adsorbed proteins studied with quantitative localized surface plasmon spectroscopy.

We have studied pH-dependent conformational transitions of Bovine Serum Albumin adsorbed onto different sizes of gold nanospheres. For larger spheres (D > 10 nm) there is evidence for a path-dependent extended state near pH 4, over a very small pH range. For smaller nanospheres (5 nm and 10 nm) the evidence for such a transition is either much weaker or completely suppressed. We suggest that the absence of the transition on small spheres is due to the fact that the protein adsorbed on such small spheres has already lost at least some of its tertiary structure. The results have important implications for the functionality of proteins adsorbed onto nanospheres or surfaces with nm scale roughness.

Quartz crystal microbalance study of protein adsorption kinetics on poly(2-hydroxyethyl methacrylate).

The interaction of macromolecules with artificial biomaterials may lead to potentially serious complications upon implantation into a biological environment. The interaction of one of the most widely used biomaterials, polyHEMA, with lysozyme, bovine serum albumin (BSA), and lactoferrin was investigated using quartz crystal microbalance (QCM). The concentration dependence of adsorption was measured for the aforementioned proteins individually as well as for lysozyme-BSA, and lysozyme-lactoferrin combinations. An extension of Voinova's viscoelastic model to n layers was used to create thickness-time graphs for adsorption. For each of lactoferrin and lysozyme, two distinctly different timescales of adsorption could be differentiated. However, the mechanisms of adsorption appeared to differ between the two. Negative dissipation shifts were measured for low concentrations of lysozyme, trending to positive dissipation at higher concentrations. This suggested that lysozyme was adsorbed initially into the matrix, stiffening the hydrogel, and later onto the surface of polyHEMA. Additionally, trials with commercial no-rub cleaning solutions indicated little added effectiveness over buffer solutions. Mixtures of proteins showed behaviour which differed in some cases from the simple combination of single protein adsorption experiments.

Size-dependent denaturing kinetics of bovine serum albumin adsorbed onto gold nanospheres.

We have used localized surface plasmon resonance (LSPR) to monitor the kinetics of thermal denaturing of bovine serum albumin (BSA) adsorbed onto gold nanospheres of size 5 nm-100 nm. The effect of the protein on the LSPR was monitored by visible extinction spectroscopy. The wavelength of the peak extinction (resonance) is affected by the conformation of the adsorbed protein layer, and as such can be used as a very sensitive probe of thermal denaturing that is specific to the adsorbed (as opposed to free) protein. The time dependence of the denaturing is measured in the temperature range 60 degrees C-70 degrees C, and the lifetimes are used to calculate an activation barrier for thermal denaturing. The results show that thermally activated denaturing of proteins adsorbed onto nanoparticles has a nanoparticle-size-dependent activation barrier, and this barrier increases for decreasing particle size. This may have important implications for other protein-nanoparticle interactions.

Anomalous thermal denaturing of proteins adsorbed to nanoparticles.

We have used localized surface plasmon resonance (LSPR) to monitor the structural changes that accompany thermal denaturing of bovine serum albumin (BSA) adsorbed onto gold nanospheres of size 5nm-60nm. The effect of the protein on the LSPR was monitored by visible extinction spectroscopy. The position of the resonance is affected by the conformation of the adsorbed protein layer, and as such can be used as a very sensitive probe of thermal denaturing that is specific to the adsorbed protein. The results are compared to detailed calculations and show that full calculations can lead to significant increases in knowledge where gold nanospheres are used as biosensors. Thermal denaturing on spheres with diameter > 20 nm show strong similarity to bulk calorimetric studies of BSA in solution. BSA adsorbed on nanospheres with d [Symbol: see text] 15nm shows a qualitative difference in behavior, suggesting a sensitivity of denaturing characteristics on local surface curvature. This may have important implications for other protein-nanoparticle interactions.

The properties of free polymer surfaces and their influence on the glass transition temperature of thin polystyrene films.

We present a detailed study of free polymer surfaces and their effects on the measured glass transition temperature (T(g)) of thin polystyrene (PS) films. Direct measurements of the near-surface properties of PS films are made by monitoring the embedding of 10 and 20 nm diameter gold spheres into the surface of spin-cast PS films. At a temperature T = 378 K( > T(g)), the embedding of the spheres is driven by geometrical considerations arising from the wetting of the gold spheres by the PS. At temperatures below T(g) (363 K < T < 370 K), both sets of spheres embed 3-4 nm into the PS films and stop. These studies suggest that a liquid-like surface layer exists in glassy PS films and also provide an estimate for the lower bound of the thickness of this layer of 3-4 nm. This qualitative idea is supported by a series of calculations based upon a previously developed theoretical model for the indentation of nanoscale spheres into linear viscoelastic materials. Comparing data with simulations shows that this surface layer has properties similar to those of a bulk sample of PS having a temperature of 374 K. Ellipsometric measurements of the T(g) are also performed on thin spin-cast PS films with thicknesses in the range 8 nm < h < 290 nm. Measurements are performed on thin PS films that have been capped by thermally evaporating 5 nm thick metal (Au and Al) capping layers on top of the polymer. The measured T(g) values (as well as polymer metal interface structure) in such samples depend on the metal used as the capping layer, and cast doubt on the general validity of using evaporative deposition to cover the free surface. We also prepared films that were capped by a new non-evaporative procedure. These films were shown to have a T(g) that is the same as that of bulk PS (370+/-1 K) for all film thicknesses measured (> 7 nm). The subsequent removal of the metal layer from these films was shown to restore a thickness-dependent T(g) in these samples that was essentially the same as that observed for uncapped PS films. An estimate of the thickness of the liquid-like surface layer was also extracted from the ellipsometry measurements and was found to be 5+/-1 nm. The combined ellipsometry and embedding studies provide strong evidence for the existence of a liquid-like surface layer in thin glassy PS films. They show that the presence of the free surface is an important parameter in determining the existence of T(g) reductions in thin PS films.

Direct imaging of nanoparticle embedding to probe viscoelasticity of polymer surfaces.

Atomic force microscopy was used to study the embedding of gold nanoparticles into the surface of polystyrene films. The rate of embedding was determined at temperatures near the bulk glass transition temperature T(g) by measuring the apparent nanosphere height as a function of annealing time. In particular, relative height measurements of the adhered particles were made at temperatures below the bulk T(g) value. In the absence of enhanced surface dynamics or yield processes no embedding is expected to occur for T