Three-dimensional structure of the shell plate assembly of the chiton Tonicella marmorea and its biomechanical consequences

This study investigates the three-dimensional structure of the eight plate exoskeletal (shell) assembly of the chiton Tonicella marmorea. X-ray micro-computed tomography and 3D printing elucidate the mechanism of conformational change from a passive (slightly curved, attached to surface) to a defensive (rolled, detached from surface) state of the plate assembly. The passive and defensive conformations exhibited differences in longitudinal curvature index (0.43 vs. 0.70), average plate-to-plate overlap (～62% vs. ～48%), cross-sectional overlap heterogeneity (60-82.5% vs. 0-90%, fourth plate), and plate-to-plate separation distance (100% increase in normalized separation distance between plates 4 and 5), respectively. The plate-to-plate interconnections consist of two rigid plates joined by a compliant, actuating muscle, analogous to a geometrically structured shear lap joint. This work provides an understanding of how T. marmorea achieves the balance between mobility and protection. In the passive state, the morphometry of the plates and plate-to-plate interconnections results in an approximately continuous curvature and constant armor thickness, resulting in limited mobility but maximum protection. In the defensive state, the underlying soft tissues gain protection and the chiton gains mobility through tidal flow, but regions of vulnerability open dorsally, due to the increase in plate-to-plate separation and decrease in plate-to-plate overlap. Lastly, experiments using optical and scanning electron microscopy, mercury porosimetry, and Fourier-transform infrared spectroscopy explore the microstructure and spatial distribution of the six layers within the intermediate plates, the role of multilayering in resisting predatory attacks, and the detection of chitin as a major component of the intra-plate organic matrix and girdle.     

Structure/function analysis of the Saccharomyces cerevisiae Trf4/Pol sigma DNA polymerase

The Trf4p/Pol sigma DNA polymerase (formerly Trf4p/Pol kappa) couples DNA replication to the establishment of sister chromatid cohesion. The polymerase is encoded by two redundant homologs in Saccharomyces cerevisiae, TRF4 and TRF5, that together define a fourth essential nuclear DNA polymerase in yeast and probably in all eukaryotes. Here we present a thorough genetic analysis of the founding member of this novel family of DNA polymerases, TRF4. Analyses of mutants carrying 1 of 34 "surface-targeted" alanine scanning mutations in TRF4 have identified those regions required for Pol sigma's essential function, for its role in DNA double-strand break repair, and for its association with chromosomes. The data strongly support the importance of the regions of predicted structural similarity with the Pol beta superfamily as critical for Trf4p/Pol sigma's essential and repair functions. Surprisingly, five lethal mutations lie outside all polymerase homology in a C-terminal region. The protein possesses Mg2+-dependent 3' to 5' exonuclease activity. Cell cycle analysis reveals that Trf4p/Pol sigma associates with chromosomes in G1, S, and G2 phases, but that association is abolished coincident with dissolution of cohesion at the metaphase-to-anaphase transition.     

A warmer environment can reduce sociability in an ectotherm

The costs and benefits of being social vary with environmental conditions, so individuals must weigh the balance between these trade-offs in response to changes in the environment. Temperature is a salient environmental factor that may play a key role in altering the costs and benefits of sociality through its effects on food availability, predator abundance, and other ecological parameters. In ectotherms, changes in temperature also have direct effects on physiological traits linked to social behaviour, such as metabolic rate and locomotor performance. In light of climate change, it is therefore important to understand the potential effects of temperature on sociality. Here, we took the advantage of a ‘natural experiment’ of threespine sticklebacks from contrasting thermal environments in Iceland: geothermally warmed water bodies (warm habitats) and adjacent ambient-temperature water bodies (cold habitats) that were either linked (sympatric) or physically distinct (allopatric). We first measured the sociability of wild-caught adult fish from warm and cold habitats after acclimation to a low and a high temperature. At both acclimation temperatures, fish from the allopatric warm habitat were less social than those from the allopatric cold habitat, whereas fish from sympatric warm and cold habitats showed no differences in sociability. To determine whether differences in sociability between thermal habitats in the allopatric population were heritable, we used a common garden breeding design where individuals from the warm and the cold habitat were reared at a low or high temperature for two generations. We found that sociability was indeed heritable but also influenced by rearing temperature, suggesting that thermal conditions during early life can play an important role in influencing social behaviour in adulthood. By providing the first evidence for a causal effect of rearing temperature on social behaviour, our study provides novel insights into how a warming world may influence sociality in animal populations.     

The pure posterior pedicle procedure for breast reduction

The inferior pedicle technique, which has already become classic, employs a glandular areola-bearing pedicle whose source of vascularization is primarily posterior. In fact, the inferior pedicle is a posterior pedicle with an inferior border. After systematically and progressively reducing this inferior border, I have completely eliminated it. The pure posterior pedicle that results is independent of the inframammary fold. It is vascularized by means of the pectoral muscle and fascia, as has been demonstrated by injection studies of the thoracoacromial artery in fresh cadavers. The resulting mammary reduction technique retains the advantages of the inferior pedicle technique while avoiding its major inconveniences: dependence on the inframammary fold, bulging at the inferior base of the pedicle, and the necessity of low positioning for the breast.     

Meal cysteine improves postprandial glucose control in rats fed a high-sucrose meal

Whey protein, particularly the alpha-lactalbumin fraction, are rich in cysteine (cys) and could therefore favor postprandial glucose homeostasis by a glutathione-mediated effect. This work investigates the effects of the ingestion of an alpha-lactalbumin-rich whey concentrate (alpha-LAC) during a high-sucrose (HS) meal on postprandial glucose homeostasis in healthy rats. In the first experiment, rats received an HS meal containing 14% protein, in which the protein source was either alpha-LAC (HS(a)) or total milk proteins, alone (HS(0)) or supplemented with 17 mg (HS(1)) or 59 mg (HS(2)) of N-acetylcysteine (NAC). This resulted in a total cys content 3.6-fold higher in the HS(1) and HS(a) meals and 12-fold higher in the HS(2) meal, when compared to the HS(0) meal. Postprandial parameters were monitored for 3 h after ingestion of the meal. The same measurements were performed on rats injected with 4 mmol/kg of buthionine sulfoximine (BSO), a specific inhibitor of glutathione synthesis. Increasing the meal's cys content dose-dependently reduced both postprandial glucose and insulin (P<.05). The inhibition of glutathione synthesis with BSO injection abrogated the beneficial effects of NAC supplementation on postprandial glucose response but did not affect those of alpha-LAC. These results show that (1) the substitution of alpha-LAC for total milk protein reduces glucose response, as does the addition of a cys donor to the meal, (2) but contrary to those of a simple cys donor, the beneficial effects of alpha-LAC are not entirely mediated by glutathione synthesis, suggesting additional mechanisms.     

Delayed hypothermia prevents decreases in N-acetylaspartate and reduced glutathione in the cerebral cortex of the neonatal pig following transient hypoxia-ischaemia

The effects of normothermia and delayed hypothermia on the levels of N-acetylaspartate (NAA), reduced glutathione (GSH) and the activities of mitochondrial complex I, II-III, IV and citrate synthase were measured in brain homogenates obtained from anaesthetized neonatal pigs following transient in vivo hypoxia-ischaemia. In the normothermic animals there was a significant decrease in complex I activity and in the levels of GSH and NAA when compared to the controls. Delayed hypothermia preserved NAA and GSH at control levels and enhanced the rate of complex II-III activity. There was correlation (R = 0.79) between GSH and NAA levels when data from all three experimental groups were analyzed. Citrate synthase activity was not significantly different in the three groups, indicating maintenance of mitochondrial integrity. These data suggest that delayed hypothermia affords protection of integrated mitochondrial function in the neonatal brain following transient hypoxia-ischaemia.