A tough biodegradable elastomer

Biodegradable polymers have significant potential in biotechnology and bioengineering. However, for some applications, they are limited by their inferior mechanical properties and unsatisfactory compatibility with cells and tissues. A strong, biodegradable, and biocompatible elastomer could be useful for fields such as tissue engineering, drug delivery, and in vivo sensing. We designed, synthesized, and characterized a tough biodegradable elastomer from biocompatible monomers. This elastomer forms a covalently crosslinked, three-dimensional network of random coils with hydroxyl groups attached to its backbone. Both crosslinking and the hydrogen-bonding interactions between the hydroxyl groups likely contribute to the unique properties of the elastomer. In vitro and in vivo studies show that the polymer has good biocompatibility. Polymer implants under animal skin are absorbed completely within 60 days with restoration of the implantation sites to their normal architecture.     

When the going gets tough,the tough get going: The enigma of survival strategies in harsh glacial stream environments

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Opposing patterns of zooplankton diversity and functioning along a natural stress gradient: when the going gets tough,the tough get going

Salinity represents a major structuring factor in aquatic habitats which strongly affects species richness. We studied the relationships among species richness, density and phylogenetic diversity of zooplankton communities along a natural salinity gradient in astatic soda pans in the Carpathian Basin (Hungary, Austria and Serbia). Diversity and density showed opposing trends along the salinity gradient. The most saline habitats had communities of one or two species only, with maximum densities well above 1000 ind l^?1. Similarity of communities increased with salinity, with most of the highly saline communities being dominated by one highly tolerant calanoid copepod, Arctodiaptomus spinosus, which was at the same time the only soda‐water specialist. Salinity obviously constrained species composition and resulted in communities of low complexity, where few tolerant species ensure high biomass production in the absence of antagonistic interactions. The pattern suggests that environmental stress may result in highly constrained systems which exhibit high rates of functioning due to these key species, in spite of the very limited species pool.     

Transfer of a parasitic sex factor to the nuclear genome of the host: A hypothesis on the evolution of sex-determining mechanisms in the terrestrial Isopod Armadillidium vulgare Latr.

In A. vulgare sex is usually determined either by a cytoplasmic feminizing factor (F symbiotic bacteria) or by another feminizing factor (f) which behaves like a mobile element of DNA and which seems to correspond to a fragment of bacterial DNA. By inhibiting the expression of male genes carried by the Z heterochromosome, these feminizing factors induce differentiation of neo-females [ZZ(+F) or ZZ(+f)]. Such a mechanism leads to the production of progenies whose sex ratio is highly female biased. In some populations in which F and/or f factors are present, genetic females (WZ) have disappeared and all individuals (males and females) are genetic males. However in other populations, cohabitation of ZZ(+f) neo-females and females in all points similar to genetic females is observed. Such a situation may be unstable and is not likely to be explainable only by migrations of individuals from distinct populations. Owing to certain types of crosses, in particular those which involve an artificial neo-male ( = female reversed into a functional male by an implant of androgenic gland) we show here that the f factor can be transmitted as a Mendelian gene. In these progenies Z_fZ females may appear: like WZ females, they breed broods whose sex ratio is unbiased. The hypothesis that the “F bacteria—A. vulgare” symbiosis may have led, after a complex co-evolutive process (F bacteria → f mobile element → insertion of f on Z heterochromosome), to the creation (from a male genotype) of a female genotype, is put forward. The consequences of such a phenomenon on the composition and the evolution of A. vulgare populations are examined.     

Intermediate filaments: not so tough after all

The dynamic properties of cellular protein polymers such as microtubules and microfilaments depend to a large extent on the cell's capacity to modify rapidly the exchange rate between polymerized and unpolymerized pools of subunits. Until quite recently the dynamic nature of intermediate filaments was underestimated because of their biochemical stability in vitro and a paucity of studies on their characteristics in vivo. However, the recent studies described in this review show that the karyoskeletal and cytoskeletal structures that assemble from many intermediate filament proteins possess the properties expected of dynamic protein polymer networks.