Abnormal arterial-venous fusions and fate specification in mouse embryos lacking blood flow.

The functions of blood flow in the morphogenesis of mammalian arteries and veins are not well understood. We examined the development of the dorsal aorta (DA) and the cardinal vein (CV) in Ncx1 -/- mutants, which lack blood flow due to a deficiency in a sodium calcium ion exchanger expressed specifically in the heart. The mutant DA and CV were abnormally connected. The endothelium of the Ncx1 -/- mutant DA lacked normal expression of the arterial markers ephrin-B2 and Connexin-40. Notch1 activation, known to promote arterial specification, was decreased in mutant DA endothelial cells (ECs), which ectopically expressed the venous marker Coup-TFII. These findings suggest that flow has essential functions in the DA by promoting arterial and suppressing venous marker expression. In contrast, flow plays a lesser role in the CV, because expression of arterial-venous markers in CV ECs was not as dramatically affected in Ncx1 -/- mutants. We propose a molecular mechanism by which blood flow mediates DA and CV morphogenesis, by regulating arterial-venous specification of DA ECs to ensure proper separation of the developing DA and CV

The impact of revitalization treatments on biological activity of soil under afforestation on post-agricultural land

In Poland, afforestation is usually carried out on the weakest soils, excluded from agricultural use and wasteland, i.e. post-agricultural land. A characteristic feature of such habitat is poor-quality soil, relatively high content of nutrients for trees, particularly nitrogen, as well as a low level of humus. This is important for the quality of microbiological processes occurring in post-agricultural soils. Restitution of the forest in such a habitat requires the use of various revitalisation treatments for improving soil quality and increasing biological activity and soil fertility. This article presents the results of a long-term experiment on the effectiveness of various revitalisation treatments (zoo- and phytomelioration) on afforested post-agricultural lands after more than 30 years from their application in pine forests in north-western Poland. These treatments consisted of introducing additional organic matter into the soil in the form of bark and sawdust, sowing lupine and introducing soil fauna. The comparative area for afforestation on post-agricultural soils in the presented experiment was the area of forest soils, located in the same habitat, in a pine stand, at the same time. Biological activity of soil was measured with the activity of soil enzymes dehydrogenases and acid phosphatase, the biomass of microorganisms was measured and the content of total dissolved carbon and nitrogen was also determined.

HOW BIOMECHANICAL IMPROVEMENTS IN RUNNING ECONOMY COULD HELP BREAK THE 2-HOUR MARATHON BARRIER

A sub-2-hour marathon requires an average velocity that is "only" 2.5% faster than the current world record of 2:02:57. A 2.5% reduction in the metabolic cost of running would enable a 2.5% faster velocity of 5.86 mls, i.e. a sub-2-hour marathon. Our analyses suggest that the metabolic cost of body wei 9 ht support could be reduced by running at the equator (slightly lower gravity = 9.78 mls ) and by pre-emptive, strategic dehydration of 2% body weight. Drafting and tailwinds could reduce the cost of forward propulsion. These biomechanical factors could each be exploited to enhance running economy by small amounts, and sum to save at least 178 seconds, permitting a time of 1:59:59

Rare plant conservation planning workshop results: Middle Park

This document identifies conservation strategies for Penland penstemon and Kremmling milkvetch, based on an assessment of the plants' viability and threats by participants of a June 2008 workshop. The primary audience is intended to be the workshop participants and other stakeholders interested in helping to implement the strategies.Sponsored by the Colorado Rare Plant Conservation Initiative, June 26, 2008

Avian Cone Photoreceptors Tile the Retina as Five Independent, Self-Organizing Mosaics

The avian retina possesses one of the most sophisticated cone photoreceptor systems among vertebrates. Birds have five types of cones including four single cones, which support tetrachromatic color vision and a double cone, which is thought to mediate achromatic motion perception. Despite this richness, very little is known about the spatial organization of avian cones and its adaptive significance. Here we show that the five cone types of the chicken independently tile the retina as highly ordered mosaics with a characteristic spacing between cones of the same type. Measures of topological order indicate that double cones are more highly ordered than single cones, possibly reflecting their posited role in motion detection. Although cones show spacing interactions that are cell type-specific, all cone types use the same density-dependent yardstick to measure intercone distance. We propose a simple developmental model that can account for these observations. We also show that a single parameter, the global regularity index, defines the regularity of all five cone mosaics. Lastly, we demonstrate similar cone distributions in three additional avian species, suggesting that these patterning principles are universal among birds. Since regular photoreceptor spacing is critical for uniform sampling of visual space, the cone mosaics of the avian retina represent an elegant example of the emergence of adaptive global patterning secondary to simple local interactions between individual photoreceptors. Our results indicate that the evolutionary pressures that gave rise to the avian retina's various adaptations for enhanced color discrimination also acted to fine-tune its spatial sampling of color and luminance