High altitude training of dogs results in elevated erythropoietin and endothelin-1 serum levels

Living at 2300-m altitude combined with intermittent training at 3500 m leads to cardiovascular alterations in dogs, including increase in systemic and pulmonary artery pressure. Despite moderate to marked hypoxemia at these altitudes, erythrocytosis does not develop. To study humoral mechanisms of acclimatisation to high altitude, erythropoietin (EPO), endothelin-1 (ET-1), big endothelin (Big-ET) and vascular endothelial growth factor (VEGF) were measured in dogs living at 2300 m and intermittently ascending to 3500 m, and compared to the values obtained in control dogs living at 700-900 m. While the median EPO and ET-1 level in dogs at 2300 m did not differ from the one measured at 700-900 m, exposure from 2300 to 3500 m resulted in significantly elevated EPO and ET-1 levels. Big-ET levels were significantly higher at 2300 and 3500 m compared to dogs at low altitude, but did not differ between 2300 and 3500 m. VEGF was significantly elevated in dogs at 2300 m compared to dogs at low altitude. The increases in EPO, VEGF, ET-1 and Big-ET are thought to reflect the effect of hypoxia on a cellular level in these dogs. Obviously, the mild elevation of EPO levels observed at 3500 m was not sufficient to cause erythrocytosis. Elevations of the vasoconstrictors Big-ET and ET-1 may play some, but not a central role in hypoxic vasoconstriction in these dogs. Finally, serum VEGF measurement may be a sensitive and useful test to assess hypoxic stress in dogs.     

Learning the codes of fly immunity

Insect antimicrobial response serves as an excellent model for studying human innate immunity. In this issue of Molecular Cell, Senger and colleagues demonstrate that a large number of immunity genes in Drosophila fat bodies can be regulated by a simple code, REL-GATA.     

Multivesicular body sorting: ubiquitin ligase Rsp5 is required for the modification and sorting of carboxypeptidase S

The multivesicular body (MVB) sorting pathway provides a mechanism for delivering transmembrane proteins into the lumen of the lysosome/vacuole. Recent studies demonstrated that ubiquitin modification acts in cis as a signal for the sorting of cargoes into this pathway. Here, we present results from a genetic selection designed to identify mutants that missort MVB cargoes. This selection identified a point mutation in ubiquitin ligase Rsp5 (Rsp5-326). At the permissive temperature, this mutant is specifically defective for ubiquitination and sorting of the ubiquitin-dependent MVB cargo precursor carboxypeptidase S (pCPS), but not ligand-induced ubiquitination of Ste2. A previous study implicated Tul1 as the ubiquitin ligase responsible for MVB sorting of pCPS. However, we detected no defect in either the sorting or ubiquitination of pCPS in tul1 mutants. We had previously shown that Fab1 phosphatidylinositol 3-phosphate 5-kinase is also required for MVB sorting of pCPS, but not Ste2. However, our analyses reveal that fab1 mutants do not exhibit a defect in ubiquitination of pCPS. Thus, both Rsp5 and Fab1 play distinct and essential roles in the targeting of biosynthetic MVB cargoes. However, whereas Rsp5 seems to be responsible for cargo ubiquitination, the precise role for Fab1 remains to be elucidated.     

The last dicynodont: an Australian Cretaceous relict

Some long-forgotten fossil evidence reveals that a dicynodont (mammal-like reptile of the infraorder Dicynodontia) inhabited Australia as recently as the Early Cretaceous, ca. 110 Myr after the supposed extinction of dicynodonts in the Late Triassic. This remarkably late occurrence more than doubles the known duration of dicynodont history (from ca. 63 Myr to ca. 170 Myr) and betrays the profound impact of geographical isolation on Australian terrestrial faunas through the Mesozoic. Australia's late-surviving dicynodont may be envisaged as a counterpart of the ceratopians (horned dinosaurs) in Cretaceous tetrapod faunas of Asia and North America.     

Never say never. The NIMA-related protein kinases in mitotic control

Mitosis sees a massive reorganization of cellular architecture. The microtubule cytoskeleton is reorganized to form a bipolar spindle between duplicated microtubule organizing centers, the chromosomes are condensed, attached to the spindle at their kinetochores, and, through the action of multiple molecular motors, the chromosomes are segregated into two daughter cells. Mitosis also sees a substantial wave of protein phosphorylation, controlling signaling events that coordinate mitotic processes and ensure accurate chromosome segregation. The key switch for the onset of mitosis is the archetypal cyclin-dependent kinase, Cdc2. Under the direction of Cdc2 is an executive of protein serine/threonine kinases that fall into three families: the Polo kinases, Aurora kinases and the NIMA-related kinases (Nrk). The latter family has proven the most enigmatic in function, although recent advances from several sources are beginning to reveal a common functional theme.     

Finite element modeling of trabecular bone damage

This paper presents a finite element-based, computational model for analysis of structural damage to trabecular bone tissues. A modulus reduction method was formulated from elasto-plasticity theory, and was used to account for site-specific trabecular bone tissue damage. Trabecular bone tissue damage is illustrated using a large-scale, anatomically accurate, two-dimensional, microstructural finite element model of a human thoracic vertebral body. Four models with varying specifications for damage accumulation were subjected to compressive loading and unloading cycles. The numerical results and experimental validation demonstrated that the modulus reduction method reproduced the non-linear mechanical behaviour of vertebal trabecular bone. The iterative computational approach presented provides a methodology to study trabecular bone damage, and should provide researchers with a computational approach to study bone fracture and repair and to predict vertebral fragility.     

Strain variation in an emerging iridovirus of warm-water fishes

Although iridoviruses vary widely within and among genera with respect to their host range and virulence, variation within iridovirus species has been less extensively characterized. This study explores the nature and extent of intraspecific variation within an emerging iridovirus of North American warm-water fishes, largemouth bass virus (LMBV). Three LMBV isolates recovered from three distinct sources differed genetically and phenotypically. Genetically, the isolates differed in the banding patterns generated from amplified fragment length polymorphism analysis but not in their DNA sequences at two loci of different degrees of evolutionary stability. In vitro, the isolates replicated at identical rates in cell culture, as determined by real-time quantitative PCR of viral particles released into suspension. In vivo, the isolates varied over fivefold in virulence, as measured by the rate at which they induced mortality in juvenile largemouth bass. This variation was reflected in the viral loads of exposed fish, measured using real-time quantitative PCR; the most virulent viral strain also replicated to the highest level in fish. Together, these results justify the designation of these isolates as different strains of LMBV. Strain variation in iridoviruses could help explain why animal populations naturally infected with iridovirus pathogens vary so extensively in their clinical responses to infection. The results of this study are especially relevant to emerging iridoviruses of aquaculture systems and wildlife.     

The structure of a cold-adapted family 8 xylanase at 1.3 A resolution. Structural adaptations to cold and investgation of the active site

Enzymes from psychrophilic organisms differ from their mesophilic counterparts in having a lower thermostability and a higher specific activity at low and moderate temperatures. The current consensus is that they have an increased flexibility, enhancing accommodation and transformation of the substrates at low energy costs. Here we describe the structure of the xylanase from the Antarctic bacterium Pseudoalteromonas haloplanktis at 1.3 A resolution. Xylanases are usually grouped into glycosyl hydrolase families 10 and 11, but this enzyme belongs to family 8. The fold differs from that of other known xylanases and can be described as an (alpha/alpha)(6) barrel. Various parameters that may explain the cold-adapted properties were examined and indicated that the protein has a reduced number of salt bridges and an increased exposure of hydrophobic residues. The crystal structures of a complex with xylobiose and of mutant D144N were obtained at 1.2 and 1.5 A resolution, respectively. Analysis of the various substrate binding sites shows that the +3 and -3 subsites are rearranged as compared to those of a family 8 homolog, while the xylobiose complex suggests the existence of a +4 subsite. A decreased acidity of the substrate binding cleft and an increased flexibility of aromatic residues lining the subsites may enhance the rate at which substrate is bound.     

Trabecular bone modulus-density relationships depend on anatomic site

One outstanding issue regarding the relationship between elastic modulus and density for trabecular bone is whether the relationship depends on anatomic site. To address this, on-axis elastic moduli and apparent densities were measured for 142 specimens of human trabecular bone from the vertebra (n=61), proximal tibia (n=31), femoral greater trochanter (n=23), and femoral neck (n=27). Specimens were obtained from 61 cadavers (mean+/-SD age=67+/-15 years). Experimental protocols were used that minimized end-artifact errors and controlled for specimen orientation. Tissue moduli were computed for a subset of 18 specimens using high-resolution linear finite element analyses and also using two previously developed theoretical relationships (Bone 25 (1999) 481; J. Elasticity 53 (1999) 125). Resultant power law regressions between modulus and density did depend on anatomic site, as determined via an analysis of covariance. The inter-site differences were among the leading coefficients (p<0.02), but not the exponents (p>0.08), which ranged 1.49-2.18. At a given density, specimens from the tibia had higher moduli than those from the vertebra (p=0.01) and femoral neck (p=0.002); those from the trochanter had higher moduli than the vertebra (p=0.02). These differences could be as large as almost 50%, and errors in predicted values of modulus increased by up to 65% when site-dependence was ignored. These results indicate that there is no universal modulus-density relationship for on-axis loading. Tissue moduli computed using methods that account for inter-site architectural variations did not differ across site (p>0.15), suggesting that the site-specificity in apparent modulus-density relationships may be attributed to differences in architecture.