Bone strain magnitude is correlated with bone strain rate in tetrapods: implications for models of mechanotransduction.

Hypotheses suggest that structural integrity of vertebrate bones is maintained by controlling bone strain magnitude via adaptive modelling in response to mechanical stimuli. Increased tissue-level strain magnitude and rate have both been identified as potent stimuli leading to increased bone formation. Mechanotransduction models hypothesize that osteocytes sense bone deformation by detecting fluid flow-induced drag in the bone's lacunar-canalicular porosity. This model suggests that the osteocyte's intracellular response depends on fluid-flow rate, a product of bone strain rate and gradient, but does not provide a mechanism for detection of strain magnitude. Such a mechanism is necessary for bone modelling to adapt to loads, because strain magnitude is an important determinant of skeletal fracture. Using strain gauge data from the limb bones of amphibians, reptiles, birds and mammals, we identified strong correlations between strain rate and magnitude across clades employing diverse locomotor styles and degrees of rhythmicity. The breadth of our sample suggests that this pattern is likely to be a common feature of tetrapod bone loading. Moreover, finding that bone strain magnitude is encoded in strain rate at the tissue level is consistent with the hypothesis that it might be encoded in fluid-flow rate at the cellular level, facilitating bone adaptation via mechanotransduction.

Prevalence of Dio2(T92A) polymorphism and its association with thyroid autoimmunity.

The 3,5,3'-L-triiodothyronine (T3) partly derives by the deiodination of the prohormone 3,5,3',5'-L-tetraiodothyronine (T4) by the type 2 iodothyronine deiodinase (D2). The single-nucleotide polymorphism in the D2 gene at position 92 (Dio(2T92A)), generates an enzyme with a reduced T4 to T3 conversion velocity. Because thyroid hormones can modulate the immune response, we hypothesized a pathophysiological role for Dio(2T92A) polymorphism in autoimmunity. The objective of this study was to investigate the Dio(2T92A) polymorphism in relation to thyroid autoimmunity (TA). We compared the prevalence of Dio(2T92A) polymorphism and serum thyroid hormone levels in healthy subjects and subjects with TA. A total of 110 subjects with TA and 106 controls were genotypized for Dio(2T92A) polymorphism. Free T3 (FT3), free T4 (FT4) and TSH were measured and compared with the Dio(2T92A) polymorphism. Dio(292T/A), Dio(292A/A), and Dio(292T/T) healthy subjects were 40.9%, 46.4%, and 12.7%, respectively. These prevalences were similar to those of some European countries whilst significantly different from that of Brazil. In the two groups of healthy subjects and TA subjects, Dio(2T92A) polymorphism had a similar distribution with non-significant differences. Similarly, no significant differences were observed in the serum concentration of FT3, FT4, and TSH between subjects with different Dio(2T92A) polymorphism. The FT4/FT3, and TSH/FT3 ratios were higher in Dio(292T/T) than in Dio(292T/A) and Dio(292A/A) subjects in both TA and healthy groups, but these differences were not significant. In conclusion, the distribution of Dio(2T92A) polymorphism may reflect geographical and ethnic differences, and it is not associated with TA.

A bizarre predatory dinosaur from the Late Cretaceous of Madagascar.

Here we report the discovery of a small-bodied (approximately 1.8 m) predatory dinosaur from the Late Cretaceous (Maastrichtian) of Madagascar. Masiakasaurus knopfleri, gen. et sp. nov., represented by several skull elements and much of the postcranial skeleton, is unique in being the only known theropod with a highly procumbent and distinctly heterodont lower dentition. Such a derived dental morphology is otherwise unknown among dinosaurs. Numerous skeletal characteristics indicate that Masiakasaurus is a member of Abelisauroidea, an enigmatic clade of Gondwanan theropods. Previously, small-bodied abelisauroids were known only from Argentina. The occurrence of Masiakasaurus on Madagascar suggests that small-bodied abelisauroids, like their larger-bodied counterparts, were more cosmopolitan, radiating throughout much of Gondwana and paralleling the diversification of small coelurosaur theropods in Laurasia.

Interaction of oxo-bridged vanadium(III) phenanthroline and bipyridine dimers with DNA.

Cationic mu-oxo V(III) dimers of the type [V2OL4Cl2]2+ (L = 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline; or 2,2'-bipyridine) are shown to interact very strongly with DNA and to lead ultimately to its degradation. Spectroscopic binding studies, electrophoreses, DNA melting temperature experiments, and other tests on the parent 1,10-phenthroline complex all yield results consistent with tight binding. However, the exact nature of the binding--i.e., intercalative, groove binding, electrostatic, or covalent--remains unclear. Resonance Raman spectroscopy is found to be a powerful method for studying the interaction of these mu-oxo V(III) dimers with DNA and shows that in frozen aqueous solution, the parent complex [V2O(phen)4Cl2]2+ undergoes initial aquation, followed by the reaction of the aquated species with the DNA. Once the V(III) dimer is bound to the DNA, redox takes place, leading to the formation of alkaline-sensitive lesions. Hydrogen peroxide is implicated as a partner in this redox event, based on the effects of the enzymes SOD and catalase.

Experimental alteration of limb posture in the chicken (Gallus gallus) and its bearing on the use of birds as analogs for dinosaur locomotion.

Extant birds represent the only diverse living bipeds, and can be informative for investigations into the life-history parameters of their extinct dinosaurian relatives. However, morphological changes that occurred during early avian evolution, including the unique adoption of a nearly horizontal femoral orientation associated with a shift in center of mass (CM), suggest that caution is warranted in the use of birds as analogs for nonavian dinosaur locomotion. In this study, we fitted a group of white leghorn chickens (Gallus gallus) with a weight suspended posterior to the hip in order to examine the effects on loading and morphology. This caused a CM shift that necessitated a change in femoral posture (by 35 degrees towards the horizontal, P < 0.001), and resulted in reorientation of the ground reaction force (GRF) vector relative to the femur (from 41 degrees to 82 degrees, P < 0.001). Despite similar strain magnitudes, an overall increase in torsion relative to bending (from 1.70 to 1.95 times bending, P < 0.001) was observed, which was weakly associated with a tendency for increased femoral cross-sectional dimensions (P = 0.1). We suggest that a relative increase in torsion is consistent with a change in femoral posture towards the horizontal, since this change increases the degree to which the bone axis and the GRF vector produce mediolateral long-axis rotation of the bone. These results support the hypothesis that a postural change during early avian evolution could underlie the allometric differences seen between bird and nonavian dinosaur femora by requiring more robust femoral dimensions in birds due to an increase in torsion.