Factors that influence the post-emergence growth in Sarcophaga falculata

The post-emergence growth (deposition of endocuticle and growth of skeletal muscles) in Sarcophaga falculata is induced by a blood-borne factor secreted from the head of the pharate adult. The secretion begins 24 to 28 hr before eclosion (at 28°C). A second blood-borne factor, appearing in the haemolymph of the flies a few hours after tanning, suppresses the post-emergence growth in flies, the heads of which have been ligatured at the time of eclosion.     

Water permeability of bilayer lipid membranes: Sterol-lipid interaction

Summary Bilayer lipid membranes were generated in an aqueous medium from synthetic, egg or plant phosphatidyl choline (PC) or from plant monogalactosyl diglyceride (MG). The water permeability of the black membranes was determined by measuring the net volume flux produced by a NaCl gradient. The osmotic permeability coefficient,P _os, was markedly affected by the number of double bonds in the fatty acid conjugates of the lipids: the greater the degree of unsaturation, the higher the value ofP _os. The temperature dependence ofP _os of the lipid membranes was studied over a range of 29 to 40°C. The experimental activation energy,E _a , estimated from the linear plots of log (P _os)versus 1/T, was significantly higher for MG membranes (17 kcal/mole) than for the various PC membranes (11 to 13 kcal/mole), probably owing to hydrogen bonding between MG and water molecules. In comparison with PC membranes, the membranes generated from PC and cholesterol (11 molar ratio) had lowerP _os but similarE _a values. Likewise, either stigmasterol or -sitosterol decreasedP _os of MG membranes, whileE _a was not affected by the sterols. MG-cholesterol membranes were specifically characterized by a unique value ofE _a (–36 kcal/mole) thus indicating temperature dependent structural changes.     

Determinants of wing-feather moult speed in songbirds

Wing morphology is known to strongly affect flight performance by affecting lift and drag during flight. Performance may consequently deteriorate during feather moult due to the creation of feather gaps in the wing. Since wing gap size may directly affect the extent of reduced flight capacity, rapid moult involving the creation of large feather gaps is expected to substantially impair flight compared with the small gaps induced by a slower moult. To examine the factors affecting wing-feather moult speed, we studied adults of nineteen resident or very short-distance migrant passerine species during their post-breeding moult using a model-selection framework following a phylogenetically controlled analysis. We examined the speed of wing-feather moult in relation to each species’ flight distance index that was estimated based on local foraging movements rather than on longer flights (e.g., migration), assessed by the Delphi technique of expert evaluation. Moult speed was also examined with respect to six morphometric variables: body mass, wing loading, the feather comprising the tip of the wing, aspect ratio, wing span, and wing area. Our results suggest that flight distance index is the most important factor determining the speed of wing-feather moult in songbirds. Species that regularly fly a shorter distance were found to moult quickly, and those that take relatively longer flights moult slowly. These results suggest that the aerodynamic cost of wing area reduction due to feather moult shapes the evolution of annual routine processes by dictating a slower moult speed (resulting in small wing gaps) for species that regularly fly long distances and consequently may be affected more substantially by large wing gaps compared with short distance flyers.     

Regulation of MAPKs by growth factors and receptor tyrosine kinases

Multiple growth- and differentiation-inducing polypeptide factors bind to and activate transmembrane receptors tyrosine kinases (RTKs), to instigate a plethora of biochemical cascades culminating in regulation of cell fate. We concentrate on the four linear mitogen-activated protein kinase (MAPK) cascades, and highlight organizational and functional features relevant to their action downstream to RTKs. Two cellular outcomes of growth factor action, namely proliferation and migration, are critically regulated by MAPKs and we detail the underlying molecular mechanisms. Hyperactivation of MAPKs, primarily the Erk pathway, is a landmark of cancer. We describe the many links of MAPKs to tumor biology and review studies that identified machineries permitting prolongation of MAPK signaling. Models attributing signal integration to both phosphorylation of MAPK substrates and to MAPK-regulated gene expression may shed light on the remarkably diversified functions of MAPKs acting downstream to activated RTKs.     

Seasonal effect of three desert halophytes on soil microbial functional diversity

The objective of this study was to evaluate the effect of some plant ecophysiological adaptations on soil microbial functional diversity in a Negev Desert ecosystem. Soil samples from the upper 0–10 cm layer were collected at the study site under three species of halophyte shrubs, Zygophyllum dumosum, Hammada scoparia, and Reaumuria negevensis. These halophytes represent the most typical cover of the Negev Desert and each of them develops complex strategies that enable greater adaptation and hence, survival. The microhabitat of the shrubs showed differences in trends and magnitude of organic matter content, electrical conductivity, total soluble nitrogen, microbial functional diversity, and C compound utilization. The trends are assumed to be driven by various mechanisms of shrub adaptation in order to be able to survive the harsh desert environment. This study provides evidence that ecophysiological strategies developed by halophytes force microbial communities (from the point of view of activity, composition, and substrate utilization) to adapt to a beneficial plant-microorganism relationship.     

Polymorphism Data Can Reveal the Origin of Species Abundance Statistics

What is the underlying mechanism behind the fat-tailed statistics observed for species abundance distributions? The two main hypotheses in the field are the adaptive (niche) theories, where species abundance reflects its fitness, and the neutral theory that assumes demographic stochasticity as the main factor determining community structure. Both explanations suggest quite similar species-abundance distributions, but very different histories: niche scenarios assume that a species population in the past was similar to the observed one, while neutral scenarios are characterized by strongly fluctuating populations. Since the genetic variations within a population depend on its abundance in the past, we present here a way to discriminate between the theories using the genetic diversity of noncoding DNA. A statistical test, based on the Fu-Li method, has been developed and enables such a differentiation. We have analyzed the results gathered from individual-based simulation of both types of histories and obtained clear distinction between the Fu-Li statistics of the neutral scenario and that of the niche scenario. Our results suggest that data for 10–50 species, with approximately 30 sequenced individuals for each species, may allow one to distinguish between these two theories.     

The ATM-mediated DNA-damage response: taking shape

Cellular responses to DNA damage are crucial for maintaining homeostasis and preventing the development of cancer. Our understanding of the DNA-damage response has evolved: whereas previously the focus was on DNA repair, we now appreciate that the response to DNA lesions involves a complex, highly branched signaling network. Defects in this response lead to severely debilitating, cancer-predisposing "genomic instability syndromes". Double strand breaks (DSBs) in DNA are potent triggers of the DNA-damage response, which is why they are used to study this pathway. The chief transducer of the DSB signal is the nuclear protein kinase ataxia-telangiectasia mutated (ATM). Genetic, biochemical and structural studies have recently provided insights into the ATM-mediated DSB response, reshaping our view of this signaling pathway while raising new questions.