Effects of competition and shading in planktonic communities

A model for several algal species which compete both for light and for nutrients, and which are also subject to settling and diffusion, is considered. The settling speeds and diffusion coefficients are assumed to be small, in a sense to be made precise later, and a singular perturbation argument is used. In certain cases vertical segregation of the algal species is observed, and the mechanism for this is interpreted biologically.Supported by the Danish Natural Science Research Council (Grant No. 11-8321)     

A new traveling-wave solution of Fisher's equation with density-dependent diffusivity

A new traveling-wave solution of Fisher's equation is found when the diffusivity is taken to be a smoothed step function of the dependent variable. The form of the solution and a necessary relationship between the traveling wave's speed and the diffusivity are predicted. This is done using flux continuity considerations in the limit when the diffusivity is piecewise constant. The predicted form is verified by numerical integration of the equation with a slightly smoothed step function diffusivity.Work performed under the auspices of the US Army Research Office (Durham), Contract DAAL03-89-K-0014; the National Science Foundation, Grant DMS87-06642; and the Air Force Office of Scientific Research, Grant AFOSR-88-0269     

Chemical models of oxidative phosphorylation

Chemical models for coupling oxidation to phosphorylation are summarized and examined both from the standpoint of organic reaction mechanisms and with respect to their relevance to mitochondria and chloroplasts. In order to accelerate the progress of our research in bioenergetics, it is suggested to focus at least as much attention on structural biochemistry as on phenomenological observations of energy-transducing membranes.Supported in part by Public Health Service Research Grant No. GM 19990 from the National Institute of General Medical Sciences and by National Science Foundation Research Grant No. PCM 74-24083 A01     

An analysis of the kinematics of swarming ofAnarete pritchardi kim (Diptera: Cecidomyiidae)

Summary Movies of swarming of a cecidomyiid midgeAnarete pritchardi Kim, are analysed to provide kinematic data for swarming. Statistical characteristics calculated from the basic data are the mean, variance, standard deviation, skewness, and kurtosis of the insect coordinates; insect number-density distribution in space, frequency distribution of insect velocities; velocity autocorrelation coefficients; effective advective velocity and diffusivity for swarming, among others. Analyses show that the motion inside the swarm is more or less random although we occasionally notice some kind of interaction between individuals. An inward velocity is detected for insects flying at the edge of the swarm. Mathematical models based on a combined process of diffusion and of nondiffusion are compared with the kinetic data to evaluate the parameters involved in the model. The result indicates that the mathematical model is realistic and useful. A few features of midge behavior in swarming flight are also noted. The result obtained for midge kinetics should be applicable to swarms of some other insects and animals. Contribution No. 211 from Chesapeake Bay Institute, Department of Earth and Planetary Sciences, The Johns Hopkins University, and Paper No. 8791 Scientific Journal Series, Agricultural Experimental Station, University of Minnesota. Supported by the Office of Naval Research under research contract N00014-67-A-0163-0006, Research Project NR083-016, and National Science Foundation Grant, GA-16603 to The Johns Hopkins University, and National Science Foundation Grant GB-1755 to the University of Minnesota.     

Chromosomal localization of silkworm (Bombyx mori) sericin gene 1 and chymotrypsin inhibitor 13 using fluorescence in situ hybridization

The chromosomal locations of two single-copy genes, Ser-1 and CI-13, in silkworm (Bombyx mori) were detected at the molecular cytogenetics level by fluorescence in situ hybridization in the study. The results showed that Ser-1 is located near the distal end of the 11th linkage group, relatively at the 12.5±1.4 position in pachytene; and that CI-13 has been mapped near the distal end of the 2nd linkage group, relatively at the 8.2±1.2 position in pachytene. Furthermore, their location model map-FISH map on silkworm chromosome was drawn. The FISH technique and its application to silkworm are also discussed in this paper.     

Changes in microtubule packing during the stretching of an extensible microtubule bundle in the ciliate Nassula

Summary The cytopharyngeal sheath in the ciliate Nassula is a long hollow tube-shaped microtubule bundle that forms part of a large feeding organelle called the cytopharyngeal basket. During the initial stages of ingestion of algal filaments by Nassula the sheath is stretched, becomes approximately elliptical in cross-section, and its external cross-sectional perimeter increases by a factor of about two. The mean circumferential centre-to-centre spacing of radially oriented rows of sheath tubules increases from 57 to 137nm during stretching but sheath thickness and the radial spacing of sheath tubules do not change appreciably. It is suggested that extensible circumferentially oriented intertubule links and relatively inextensible radial links may define the anisometric mechanical properties of this particular microtubule bundle which are related to its cytoskeletal role. The possibility that extensible links resist stretching elastically and provide the restoring forces for return of the sheath to its former shape and dimensions after stretching is considered.Supported by the Science Research Council, U.K. (Grant nos. B/RG/5894.5 and GR/A/0875.8)     

Direct innervation of the mantle edge gland by neurosecretory axons in Helisoma duryi (Mollusca: Pulmonata)

Summary The mantle edge gland of Helisoma duryi is innervated by neurosecretory axons from the pallial nerves. Synaptoid contacts occur between axons and gland cells, and there is ultrastructural evidence for the release of neurosecretory material. The mantle edge gland contributes to the deposition of periostracum during shell formation, and direct neurosecretory innervation may control shell growth and regeneration.Supported by a National Research Council of Canada Grant (A-4673) and Negotiated Grant D-61     

On the stability of a model of testosterone dynamics

We prove the global asymptotic stability of a well-known delayed negative-feedback model of testosterone dynamics, which has been proposed as a model of oscillatory behavior. We establish stability (and hence the impossibility of oscillations) even in the presence of delays of arbitrary length.Supported in part by AFOSR Grant F49620-01-1-0063, NIH Grant P20 GM64375, and Dimacs.E.D. Sontag: Supported in part by AFOSR Grant F49620-01-1-0063 and NIH Grant R01 GM46383.Acknowledgement We would like to thank Augusto Ponce for useful suggestions.     

Interspecies transmission and host restriction of avian H5N1 influenza virus

Long-term endemicity of avian H5N1 influenza virus in poultry and continuous sporadic human infections in several countries has raised the concern of another potential pandemic influenza. Suspicion of the avian origin of the previous pandemics results in the close investigation of the mechanism of interspecies transmission. Entry and fusion is the first step for the H5N1 influenza virus to get into the host cells affecting the host ranges. Therefore receptor usage study has been a major focus for the last few years. We now know the difference of the sialic acid structures and distributions in different species, even in the different parts of the same host. Many host factors interacting with the influenza virus component proteins have been identified and their role in the host range expansion and interspecies transmission is under detailed scrutiny. Here we review current progress in the receptor usage and host factors. Supported by the National Basic Research Program of China (Grant Nos. 2005CB523001, 2005CB523002), National Key Technologies Research & Development Program (Grant 2006BAD06A01/2006BAD06A04); US National Institutes of Health (NIH) (Grant 3 U19 AI051915-05S1), the National Natural Science Foundation of China (Grant 30599434). GAO FG is a distinguished young investigator of the NSFC (Grant No. 30525010).     

Histochemical activation of rat-liver lysosomes by dimethyl sulfoxide

Summary The Gomori reaction for acid phosphatase was enhanced by inclusion of dimethyl sulfoxide (DMSO) in reaction media for incubation of cryostat sections of unfixed rat-liver tissue. The reaction was also detectably increased by DMSO in formol-calcium fixed tissue. Enhancment of the Gomori reaction for acid phosphatase by DMSO was reversible.Supported by Grant GB-3817 from the National Science Foundation and by the University Research Coucil and the Cancer Institutional Grant Committee of the University of North Carolina     

Numerical solution of a nonlinear advance-delay-differential equation from nerve conduction theory

A functional differential equation which is nonlinear and involves forward and backward deviating arguments is solved numerically. The equation models conduction in a myelinated nerve axon in which the myelin completely insulates the membrane, so that the potential change jumps from node to node. The equation is of first order with boundary values given at t=±. The problem is approximated via a difference scheme which solves the problem on a finite interval by utilizing an asymptotic representation at the endpoints, cubic interpolation and iterative techniques to approximate the delays, and a continuation method to start the procedure. The procedure is tested on a class of problems which are solvable analytically to access the scheme's accuracy and stability, then applied to the problem that models propagation in a myelinated axon. The solution's dependence on various model parameters of physical interest is studied. This is the first numerical study of myelinated nerve conduction in which the advance and delay terms are treated explicitly.Supported in part by NSF Grant MCS8301724 and by a Biomedical Research Support Grant 2SO7RR0706618 from NIH     

Developing a microfluidic-based system to quantify cell capture efficiency

Micro-fabrication technology has substantial potential for identifying molecular markers expressed on the surfaces of tissue cells and viruses. It has been found in several conceptual prototypes that cells with such markers are able to be captured by their antibodies immobilized on microchannel substrates and unbound cells are flushed out by a driven flow. The feasibility and reliability of such a microfluidic-based assay, however, remains to be further tested. In the current work, we developed a microfluidic-based system consisting of a microfluidic chip, an image grabbing unit, data acquisition and analysis software, as well as a supporting base. Specific binding of CD59-expressed or BSA-coupled human red blood cells (RBCs) to anti-CD59 or anti-BSA antibody-immobilized chip surfaces was quantified by capture efficiency and by the fraction of bound cells. Impacts of respective flow rate, cell concentration, antibody concentration and site density were tested systematically. The measured data indicated that the assay was robust. The robustness was further confirmed by capture efficiencies measured from an independent ELISA-based cell binding assay. These results demonstrated that the system developed provided a new platform to effectively quantify cellular surface markers effectively, which promoted the potential applications in both biological studies and clinical diagnoses. Supported by the National Key Basic Research Program of China (Grant No. 2006CB910303), National Natural Science Foundation of China (Grant Nos. 30730032 and 10332060), National High-Tech Research and Development Program of China (Grant No. 2007AA02Z306) and Chinese Academy of Sciences Grant (Grant No.2005-1-16)     

Multi-species interactions with hereditary effects and spatial diffusion

Summary We study the effect of spatial diffusion on oscillatory states in arbitrary multi-species growth models having hereditary terms. We show that it is a general principle that the addition of spatial diffusion to a stable oscillatory ecological community induces a periodic diffusion wave in which the original wavenumber (or phase) evolves according to a nonlinear evolution equation of generalized Burgers' type.Supported in part by the U.S. Army Research Office (Durham) under Contract DAHC-04-68-C-0006 and by the National Science Foundation under Grant GP-32157X2     

Are small RNAs a big help to plants?

The discovery of RNA interference (RNAi) has augmented our knowledge of gene regulation and presents a fascinating technology that has a great potential for application in genetic analysis, disease therapy, plant protection, and many other areas. In this review, we will focus on the biological functions of RNAi and its application in agriculture with a brief introduction to the history of its discovery and molecular mechanism. Supported by National Natural Sciences of China (Grant No. 30630008) and National Key Basic Research and Development Program of China (Grant No. 2007CB108800).     

Interstitial deletion in the “critical region” of the long arm of the X chromosome in a mentally retarded boy and his normal mother

Summary A family in which an interstitial deletion of the X chromosome, del(X)(q13q21.3), is segregating was ascertained through a boy with cleft lip and palate, agenesis of the corpus callosum, and severe mental retardation. The possible causal relationship to his chromosome abnormality is discussed. Although the deletion occurred within the critical region, the mother showed no signs of gonadal dysgenesis. A phenotypically normal daughter was, as her mother, monosomic for this region of the X, and both showed random inactivation of the X chromosome.Supported in part by grants to E.N. from the Carl Petersen's Foundation (B 995) and the Danish Medical Research Council (512-4276)     

Current research status of immunology in the genomic era

This review updates the current status of immunology research under the influence of genomics, both conceptually and technologically. It particularly highlights the advantages of employing the high-throughput and large-scale technology, the large genomic database, and bioinformatic power in the immunology research. The fast development in the fields of basic immunology, clinical immunology (tumor and infectious immunology) and vaccine designing is illustrated with respect to the successful usage of genomic strategy. We also speculate the future research directions of immunology in the era of genomics and post-genomics. Supported by the National High-Tech Research and Development Program of China (Grant No.2006AA02A252), National Natural Science Foundation of China (Grant No.30771965) and Shanghai Pujiang Program (Grant No.07pj14066).     

Fractionation of RNA from tetrahymena by affinity chromatography on poly-u-sepharose

Summary Exponential growing Tetrahymena pyriformis organisms were labelled with (³H) uridine or (³H) adenosine. The labelled RNA was extracted and isolated by affinity chromatography on poly-uridylic-acid Sepharose and further analysed by means of sucrose gradient centrifugation and RNase digestion.Experimental evidence proved the existence of RNase resistant poly adenylic-acid fragments in the RNA of Tetrahymena cells. This poly adenylic-acid segment has a sedimentation rate of 4-5 S and would be localised in the 10-12S region of the RNA which is probably the m-RNA.Supported by Stiftung Volkswagenwerk Research Grant No.112273.     

On using cis-Pt (II)-uracil as a stain for nucleic acids in brain slices and subcellular fractions

Summary Chick brain cortical slices and crude mitochondrial fractions were fixed with glutaraldehyde, stained only with cis-Pt (II)-uracil and processed for electron microscopy. The optimal time of staining was determined to be 10 min. Results show that this platinum-pyrimidine complex is a relatively specific stain for the nucleic acids of brain slices. However, staining of crude mitochondrial fractions apparently resulted in some protein staining and other artifacts. The method should be helpful identifying ribosomal contamination of subcellular preparations and if its specificity can be increased it may prove a useful addition to staining methods of the electron microscopist.Supported by NIH Grant NS-12485, Grant P-593 from the Robert A. Welch Foundation, and Grant C-7561 from the TCU Research Foundation     

Conduction in demyelinated axons—A simplified model

This paper is concerned with conduction of the nervous impulse in a myelinated axon and the effect of demyelination on conduction characteristics. A model of nerve conduction called the “gunpowder fuse” model is presented which accurately predicts conduction velocities in both myelinated and unmyelinated nerves. The effect on conduction velocity in this model by reducing myelin thickness is examined by utilizing basic data and building and equivalent circuit. The result is a curve relating reduced conduction velocity to reduced myelin thickness. A similar analysis and resultant curve is derived from a saltatory conduction model. Supported in part by National Multiple Sclerosis Society Research Grant No. 516 and Air Force Grant AFOSR 669-67.     

Screening and breeding of high taxol producing fungi by genome shuffling

To apply the fundamental principles of genome shuffling in breeding of taxol-producing fungi, Nodulisporium sylviform was used as starting strain in this work. The procedures of protoplast fusion and genome shuffling were studied. Three hereditarily stable strains with high taxol production were obtained by four cycles of genome shuffling. The qualitative and quantitative analysis of taxol produced was confirmed using thin-layer chromatography (TLC), high performance liquid chromatography (HPLC) and LC-MS. A high taxol producing fungus, Nodulisporium sylviform F4-26, was obtained, which produced 516.37 μg/L taxol. This value is 64.41% higher than that of the starting strain NCEU-1 and 31.52%―44.72% higher than that of the parent strains.