Identification of novel chondroitin proteoglycans in Caenorhabditis elegans: embryonic cell division depends on CPG-1 and CPG-2.

Vertebrates produce multiple chondroitin sulfate proteoglycans that play important roles in development and tissue mechanics. In the nematode Caenorhabditis elegans, the chondroitin chains lack sulfate but nevertheless play essential roles in embryonic development and vulval morphogenesis. However, assignment of these functions to specific proteoglycans has been limited by the lack of identified core proteins. We used a combination of biochemical purification, Western blotting, and mass spectrometry to identify nine C. elegans chondroitin proteoglycan core proteins, none of which have homologues in vertebrates or other invertebrates such as Drosophila melanogaster or Hydra vulgaris. CPG-1/CEJ-1 and CPG-2 are expressed during embryonic development and bind chitin, suggesting a structural role in the egg. RNA interference (RNAi) depletion of individual CPGs had no effect on embryonic viability, but simultaneous depletion of CPG-1/CEJ-1 and CPG-2 resulted in multinucleated single-cell embryos. This embryonic lethality phenocopies RNAi depletion of the SQV-5 chondroitin synthase, suggesting that chondroitin chains on these two proteoglycans are required for cytokinesis

Sequential primed kinases create a damage-responsive phosphodegron on Eco1.

Sister-chromatid cohesion is established during S phase when Eco1 acetylates cohesin. In budding yeast, Eco1 activity falls after S phase due to Cdk1-dependent phosphorylation, which triggers ubiquitination by SCF(Cdc4). We show here that Eco1 degradation requires the sequential actions of Cdk1 and two additional kinases, Cdc7-Dbf4 and the GSK-3 homolog Mck1. These kinases recognize motifs primed by previous phosphorylation, resulting in an ordered sequence of three phosphorylation events on Eco1. Only the latter two phosphorylation sites are spaced correctly to bind Cdc4, resulting in strict discrimination between phosphates added by Cdk1 and by Cdc7. Inhibition of Cdc7 by the DNA damage response prevents Eco1 destruction, allowing establishment of cohesion after S phase. This elaborate regulatory system, involving three independent kinases and stringent substrate selection by a ubiquitin ligase, enables robust control of cohesion establishment during normal growth and after stress

Elastic behaviour of a regular lattice for meso-scale modelling of solids

AbstractA modelling strategy is proposed to link the meso-scale mechanical response of a solid material to the macroscopic material behaviour. The model is based on a regular lattice of truncated octahedral cells, with sites at the cell centres linked by two sets of bonds. The relationship between the macroscopic elastic behaviour of the model and the elastic properties of the bonds is studied numerically. The results demonstrate that, in contrast to previously proposed lattice arrangements, any elastic properties of metallic or cementitious materials can be obtained by appropriate selection of the axial and the shear stiffness of the bonds. Discussion of the modelling approach includes the potential of the site-bond model to simulate the evolution of damage driven not only by mechanical deformation but also by processes that involve the interaction of different mechanisms

Wolverine Reproductive Den Habitat in Glacier National Park, Montana

Wolverine reproductive dens occur in habitat not easily accessible to humans during the denning period (Feb – May) and can be challenging to find.  As such, few den sites have been precisely described. From 2003 – 2007 we located and documented 14 natal and maternal dens of 3 reproductive female wolverine in Glacier National Park.  Two females were known to have produced young in multiple years, using different den sites each year.  Reproductive dens occurred at an average elevation of 1890m (range: 1805-1999m), on 9° slopes (range: 5-22o), within a variable range of aspects (   =263°), and with an average snow depth of 2.6m (range: 2.4-3.4m). Den structures included downed trees, large boulders, and rock caves associated with alpine cirques, ridges, and cliff bands at, or below, existing tree line.  Distance to occupied human development averaged 6.4km, and distance between denning areas of the same female in different years averaged 5.8 km.  Various climate change models predict less persistent snowpack in many areas of the conterminous United States, with a resultant potential for increased isolation of island populations of wolverines

Wolverine Food Habitats and Foraging Strategies in Glacier National Park, Montana

From 2003-2007 we captured and instrumented 28 wolverines (Gulo gulo) in Glacier National Park to investigate reproduction and recruitment. We collected 189 scat samples at reproductive den, forage and rendezvous sites, and documented 90 prey species through observation and prey remains found at similar sites. Seasonal scat analysis provided evidence of differences in prey species consumed during winter (n = 170), summer (n = 19), and reproductive den (n = 103) periods. Ungulates were the most frequently observed prey found in all scats (71%; N=135), with Cervid remains being observed most often (37%; n = 70). Hibernating rodents (ground squirrels and marmots) (36%; n = 68) were the next most utilized prey, with the third most documented prey being mice and voles (31%; n = 56). Vegetation (72%; n = 169), soil material (31%; n = 59), and bone (90%; n = 171) were also found in scats. Seasonal importance of prey was documented, with ungulates being the most observed prey in winter scats (75%; n = 128) and den period scats (79%; n = 81), and hibernating rodents being most observed in summer scats (47%; n = 9). A similar condition was found with analysis of all prey remains (n = 90); ungulates were consumed most often (69%; n = 63), with hibernating rodents as the second most documented prey (12%; n = 11). Wolverines exhibited seasonal dietary shifts in that ungulates were consumed most frequently during winter (77%; n = 55) and the den period (78%; n = 17), with hibernating rodents the most frequent prey documented in summer (50%; n = 9). Wolverine foraging strategies, including searching tree wells, fishing, decapitation, and food caching are also discussed