Design of Active Transport Must Be Highly Intricate: A Possible Role of Myosin and Ena/VASP for G-Actin Transport in Filopodia

Recent modeling of filopodia—the actin-based cell organelles employed for sensing and motility—reveals that one of the key limiting factors of filopodial length is diffusional transport of G-actin monomers to the polymerizing barbed ends. We have explored the possibility of active transport of G-actin by myosin motors, which would be an expected biological response to overcome the limitation of a diffusion-based process. We found that in a straightforward implementation of active transport the increase in length was unimpressive, ≤30%, due to sequestering of G-actin by freely diffusing motors. However, artificially removing motor sequestration reactions led to approximately threefold increases in filopodial length, with the transport being mainly limited by the motors failing to detach from the filaments near the tip, clogging the cooperative conveyer belt dynamics. Making motors sterically transparent led to a qualitative change of the dynamics to a different regime of steady growth without a stationary length. Having identified sequestration and clogging as ubiquitous constraints to motor-driven transport, we devised and tested a speculative means to sidestep these limitations in filopodia by employing cross-linking and putative scaffolding roles of Ena/VASP proteins. We conclude that a naïve design of molecular-motor-based active transport would almost always be inefficient—an intricately organized kinetic scheme, with finely tuned rate constants, is required to achieve high-flux transport.     

Determination of the sensitivity of head lice to insecticides]

The author recommends a method of determination of sensitivity of head lice which, in difference from the accepted one, is based on the establishment of the time interval between the death of 50-100% of the insects as a result of the contact with the insecticide in definite doses of the active substance. The method permits to assess the rapidity and the extent of the toxic action of various substances on lice; it is simple and convenient for use in practice.     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

No relation between ACEml/D polymorphism and high altitude pulmonary edema in the Han Chinese

Objectives To explore whether the angiotensin T -converting enzyme （ACE） I/D （insertion/ deletion） polymorphism is associated with the susceptibility to high altitude pulmonary edema （HAPE） in the Han Chinese. Methods One hundred and forty-seven HAPE-p （HAPE patients） and 193 HAPE-r （HAPE resistants） were enrolled from the Yushu earthquake reconstruction workers in Qinghai province where the altitude is over 3 500 m above sea level. Blood samples were collected from each of the HAPE-p and HAPE-r groups. Information about physiological phenotypes was obtained via fieldwork investigation. The ACE-I/D polymorphism in HAPE-p and HAPE-r was detected by polymerase chain reaction （PCR）. Results The SaO2 was significantly lower while HR was significantly higher in HAPE-p group than those in HAPE-r group. The genotype frequencies of ACE-I/D for II, ID, DD in HAPE-r and HAPE-p groups were 0.430, 0.446, 0.124 and 0.435, 0.469, 0.095, respectively, the allelic frequencies of I and D were 0.650, 0.350 and 0.670, 0.330, respectively. The OR of ID, DD and D alleles relative to II for HAPE was 0.961 （0.610-1.514）, 1.322 （0.634-2.758） and 1.080 （0.783-1.489）. There was no significant difference of the genotypic and the allelic frequencies in ACE-I/D polymorphism between HAPE-p and HAPE-r groups. Conclusions There is no relation between ACE-I/D polymorphism and HAPE in the Han Chinese.