Stem cells find their niche.

The concept that stem cells are controlled by particular microenvironments known as 'niches' has been widely invoked. But niches have remained largely a theoretical construct because of the difficulty of identifying and manipulating individual stem cells and their surroundings. Technical advances now make it possible to characterize small zones that maintain and control stem cell activity in several organs, including gonads, skin and gut. These studies are beginning to unify our understanding of stem cell regulation at the cellular and molecular levels, and promise to advance efforts to use stem cells therapeutically.     

Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution.

Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 A resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.     

Body fat, body water, and total caloric value of Uinta ground squirrels

The weight of body water and fat-free dry weight of Uinta ground squirrels ( Spermophilus armatus ) is given as a function of body weight. Body fat is presented as a function of body weight and body length. An equation for calculating the total caloric content of Uinta ground squirrels is given. Fat index (weight of fat/fat-free dry weight) values of juveniles increased from 0.11 to 0.22 from 5 June to 28 July. In male yearlings and adults the fat index increased about 8 to 9 times in the latter half of June and early July.         

Catastrophic wildfire and number of populations as factors influencing risk of extinction for Gila trout ( Oncorhynchus gilae )

We used the computer program RAMAS to explore the sensitivity of an extinction-risk model for the Gila trout ( Oncorhynchus gilae ) to management of wildfires and number of populations of the species. The Gila trout is an endangered salmonid presently restricted to very few headwaters of the Gila and San Francisco river tributaries in southwestern New Mexico. Life history data for 10 extant populations were used to examine sensitivity of the species viability to changes in a variety of factors including population size, fecundity, life stage structure, number of populations, severity and probability of forest fires, and a regulated fishery. The probability and severity of forest fires and number of populations had the greatest effect on viability. Results indicate that successful conservation of Gila trout requires establishment of additional populations and reduction of the severity of forest fires through a program incorporating more frequent, but less severe, fires.     

Richard Watson

The development of the circular dividing engine in England is traced from Henry Hindley and Jesse Ramsden through the improvements introduced by Ramsden's successors to the self-acting engine of William Simms. Particular emphasis is given to the invention, evolution and transmission of the methods used to achieve accuracy in: dividing the wheel; ratching the teeth and matching them to the endless screw; and mounting the cutter. The procedures adopted by Ramsden and Troughton for correcting initial dividing marks are also described.     

Distribution records and comments on fleas in southwestern South Dakota

From October 2003 through April 2006, we collected 565 fleas incidental to a distribution survey of mammals in southwestern South Dakota. Sixty-one specimens, representing 18 species of mammals, possessed 20 species of fleas. The geographic distributions of these flea species revealed 8 new records for the Black Hills and its adjacent grasslands. Four species— Megarthroglossus divisus, Stenoponia americana, Odontopsyllus dentatus, and Amaradix euphorbi —constitute new records for South Dakota, thus increasing the state’s known flea fauna to 42 species. Hunters, trappers, and field biologists should be aware that serosurveillance during the 1990s revealed the presence of sylvatic plague and tularemia in the Black Hills area. Desde octubre de 2003 hasta abril de 2006, colectamos 565 pulgas de manera incidental durante un estudio de la distribución de mamíferos en el suroeste del estado de Dakota del Sur. Los 61 especímenes, que representaban 18 especies de mamíferos, albergaban 20 especies de pulgas. Sus distribuciones geográficas revelaron 8 nuevos registros para las Colinas Negras (Black Hills) y las praderas adyacentes. Cuatro de estas especies ( Megarthroglossus divisus, Stenoponia americana, Odontopsyllus dentatus y Amaradix euphorbi ) constituyen nuevos registros para Dakota del Sur. Esto aumenta el número de especies de pulgas conocidas del estado a 42 especies. Los cazadores, tramperos y biólogos de campo deben estar conscientes de que la vigilancia serológica durante la década de los 1990 reveló la presencia de la plaga silvática y la tularemia en el área de las Colinas Negras.     

Vaccination against and treatment of tuberculosis, the leishmaniases and AIDS: perspectives from basic immunology and immunity to chronic intracellular infections

The occurrence of infectious disease represents a failure of the immune system, a failure that must be prevented by effective vaccination or remedied by treatment. Vaccination against acute diseases such as smallpox and polio are very effective, due to the rapid and increased immune response of vaccinated individuals upon natural infection. In contrast, effective vaccination against intracellular pathogens that cause chronic diseases, such as the leishmaniases, tuberculosis and AIDS, has not been achieved. Clinical observations suggest cell-mediated, Th1 responses, exclusive of antibody production and the generation of Th2 cells, are optimally protective against these intracellular pathogens. Effective vaccination must ensure the generation of such a protective response. We explore here whether understanding very broad features of the regulation of the immune response can accommodate modern findings on the immunological features of these diseases, and provide a perspective within which strategies for effective vaccination and treatment can be developed.