Optimizing countershading camouflage.

Countershading, the widespread tendency of animals to be darker on the side that receives strongest illumination, has classically been explained as an adaptation for camouflage: obliterating cues to 3D shape and enhancing background matching. However, there have only been two quantitative tests of whether the patterns observed in different species match the optimal shading to obliterate 3D cues, and no tests of whether optimal countershading actually improves concealment or survival. We use a mathematical model of the light field to predict the optimal countershading for concealment that is specific to the light environment and then test this prediction with correspondingly patterned model "caterpillars" exposed to avian predation in the field. We show that the optimal countershading is strongly illumination-dependent. A relatively sharp transition in surface patterning from dark to light is only optimal under direct solar illumination; if there is diffuse illumination from cloudy skies or shade, the pattern provides no advantage over homogeneous background-matching coloration. Conversely, a smoother gradation between dark and light is optimal under cloudy skies or shade. The demonstration of these illumination-dependent effects of different countershading patterns on predation risk strongly supports the comparative evidence showing that the type of countershading varies with light environment.

Array comparative genomic hybridization for diagnosis of developmental delay: an exploratory cost-consequences analysis.

A major application of array comparative genomic hybridization (aCGH) is to define a specific cause in children with undiagnosed learning and developmental disability (LDD). Medical notes for 46 consecutive patients selected for aCGH analysis by clinical dysmorphologists were abstracted for clinical investigations related to LDD and a cost-consequences analysis was performed. aCGH analysis was completed in 36 cases and five diagnostic chromosomal anomalies were identified (13.8%). The number of investigations undertaken on each child varied. With aCGH estimated to cost 590 British Pound per case, if aCGH had been undertaken after negative standard initial tests for LDD investigation, the additional cost would be 2399 British Pound per positive case. If the cost of aCGH was reduced to 256 British Pound per case (approximately 350 Euro), aCGH becomes cost neutral. All chromosomal anomalies detected by aCGH had a de Vries score of > or =5. If aCGH had only been used for individuals with a score of > or =5, the sensitivity increased to 21.7% yielding a cost of 1087 British Pound per positive case identified. Pre-selection of cases for aCGH based on de Vries criteria has a major economic impact on introducing aCGH into clinical practice. Prospective studies are required to explore the long-term costs and consequences of aCGH and identify when aCGH may provide the most benefit at least cost.

Unfolding and refolding of cytochrome c driven by the interaction with lipid micelles.

Binding of native cyt c to L-PG micelles leads to a partially unfolded conformation of cyt c. This micelle-bound state has no stable tertiary structure, but remains as alpha-helical as native cyt c in solution. In contrast, binding of the acid-unfolded cyt c to L-PG micelles induces folding of the polypeptide, resulting in a similar helical state to that originated from the binding of native cyt c to L-PG micelles. Far-ultraviolet (UV) circular dichroism (CD) spectra showed that this common micelle-associated helical state (HL) has a native-like alpha-helix content, but is highly expanded without a tightly packed hydrophobic core, as revealed by tryptophan fluorescence, near-UV, and Soret CD spectroscopy. The kinetics of the interaction of native and acid-unfolded cyt c was investigated by stopped-flow tryptophan fluorescence. Formation of H(L) from the native state requires the disruption of the tightly packed hydrophobic core in the native protein. This micelle-induced unfolding of cyt c occurs at a rate approximately 0.1 s(-1), which is remarkably faster in the lipid environment compared with the expected rate of unfolding in solution. Refolding of acid-unfolded cyt c with L-PG micelles involves an early highly helical collapsed state formed during the burst phase (<3 ms), and the observed main kinetic event reports on the opening of this early compact intermediate prior to insertion into the lipid micelle.