Social parasites

Protozoan parasites cause tremendous human suffering worldwide, but strategies for therapeutic intervention are limited. Recent studies illustrate that the paradigm of microbes as social organisms can be brought to bear on questions about parasite biology, transmission and pathogenesis. This review discusses recent work demonstrating adaptation of social behaviors by parasitic protozoa that cause African sleeping sickness and malaria. The recognition of social behavior and cell-cell communication as a ubiquitous property of bacteria has transformed our view of microbiology, but protozoan parasites have not generally been considered in this context. Works discussed illustrate the potential for concepts of sociomicrobiology to provide insight into parasite biology and should stimulate new approaches for thinking about parasites and parasite-host interactions.     

Genetic and environmental heterogeneity of residual variance of weight traits in Nellore beef cattle

Background

Many studies have provided evidence of the existence of genetic heterogeneity of environmental variance, suggesting that it could be exploited to improve robustness and uniformity of livestock by selection. However, little is known about the perspectives of such a selection strategy in beef cattle.

Methods

A two-step approach was applied to study the genetic heterogeneity of residual variance of weight gain from birth to weaning and long-yearling weight in a Nellore beef cattle population. First, an animal model was fitted to the data and second, the influence of additive and environmental effects on the residual variance of these traits was investigated with different models, in which the log squared estimated residuals for each phenotypic record were analyzed using the restricted maximum likelihood method. Monte Carlo simulation was performed to assess the reliability of variance component estimates from the second step and the accuracy of estimated breeding values for residual variation.

Results

The results suggest that both genetic and environmental factors have an effect on the residual variance of weight gain from birth to weaning and long-yearling in Nellore beef cattle and that uniformity of these traits could be improved by selecting for lower residual variance, when considering a large amount of information to predict genetic merit for this criterion. Simulations suggested that using the two-step approach would lead to biased estimates of variance components, such that more adequate methods are needed to study the genetic heterogeneity of residual variance in beef cattle.     

Glutamine-valine index — An aid in the detection of urea-cycle disorders

Summary By relating the increase in glutamine to the corresponding increase in valine following protein loading it has been possible to detect carriers of OCT deficiency.     

The uptake of Zn,Mn, Cu and B from spray mixtures by navel orange leaves

Summary The effect of spray mixtures containing Zn, Mn, Cu, and B on the leaf levels of these elements in navel oranges was investigated in the Rustenburg area, South Africa.Foliar applications increased the levels of Zn, Mn, and B satisfactorily. The uptake of Mn appeared to be independent of complementary ions. Certain discrepancies observed in the uptake of other elements warrant further investigation. re]19720808     

Human Pancreatic Islet Isolation: Part II: Purification and Culture of Human Islets

Management of Type 1 diabetes is burdensome, both to the individual and society, costing over 100 billion dollars annually. Despite the widespread use of glucose monitoring and new insulin formulations, many individuals still develop devastating secondary complications. Pancreatic islet transplantation can restore near normal glucose control in diabetic patients ¹, without the risk of serious hypoglycemic episodes that are associated with intensive insulin therapy. Providing sufficient islet mass is important for successful islet transplantation. However, donor characteristics, organ procurement and preservation affect the isolation outcome ². At University of Illinois at Chicago (UIC) we developed a successful isolation protocol with an improved purification gradient ³. The program started in January 2004 and more than 300 isolations were performed up to November 2008. The pancreata were sent in cold preservation solutions (UW, University of Wisconsin or HTK, Histidine-Tryptophan Ketoglutarate) ^4-7 to the Cell Isolation Laboratory at UIC for islet isolation. Pancreatic islets were isolated using the UIC method, which is a modified version of the method originally described by Ricordi et al⁸. As described in Part I: Digestion and Collection of Pancreatic Tissue, human pancreas was trimmed, cannulated, perfused, and digested. After collection and at least 30 minutes of incubation in UW solution, the tissue was loaded in the cell separator (COBE 2991, Cobe, Lakewood, CO) for purification ³. Following purification, islet yield (expressed as islet equivalents, IEQ), tissue volume, and purity was determined according to standard methods ⁹. Isolated islets were cultured in CMRL-1066 media (Mediatech, Herndon, VA), supplemented with 1.5% human albumin, 0.1% insulin-transferrin-selenium (ITS), 1 ml of Ciprofloxacin, 5 ml o f 1M HEPES, and 14.5 ml of 7.5% Sodium Bicarbonate in T175 flasks at 37°C overnight culture before islets were transplanted or used for research.Open in a separate windowClick here to view.^{(52M, flv)}     

The Influence of Specific Neighboring Bases on Substitution Bias in Noncoding Regions of the Plant Chloroplast Genome

Substitutions occurring in noncoding sequences of the plant chloroplast genome violate the independence of sites that is assumed by substitution models in molecular evolution. The probability that a substitution at a site is a transversion, as opposed to a transition, increases significantly with increasing A + T content of the two adjacent nucleotides. In the present study, this dependency of substitutions on local context is examined further in a number of noncoding regions from the chloroplast genome of members of the grass family (Poaceae). Two features were examined; the influence of specific neighboring bases, as opposed to the general A + T content, on transversion proportion and an influence on substitutions by nucleotides other than the two immediately adjacent to the site of substitution. In both cases, a significant effect was found. In the case of specific nucleotides, transversion proportion is significantly higher at sites with a pyrimidine immediately 5′ on either strand. Substitutions at sites of the type YNR, where N is the site of substitution, have the highest rate of transversion. This specific effect is secondary to the A + T content effect such that, in terms of proportion of substitutions that are transversions, the nucleotides are ranked T > A > C > G as to their effect when they are immediately 5′ to the site of substitution. In the case of nucleotides other than the immediate neighbors, a significant influence on substitution dynamics is observed in the case where the two neighboring bases are both A and/or T. Thus, substitutions are primarily, but not exclusively, influenced by the composition of the two nucleotides that are immediately adjacent. These results indicate that the pattern of molecular evolution of the plant chloroplast genome is extremely complex as a result of a variety of inter-site dependencies. Received: 18 October 1996 / Accepted: 12 April 1997     

The degree of stacking and the average membrane area of thylakoids in lettuce chloroplasts

The surface density of stacked and total thylakoid membranes in chloroplasts was determined morphometrically using the method of vertical sections. The degree of stacking, defined as the fraction of the total membrane area which is involved in stacking, was calculated from the surface densities and found to be 0.70 for chloroplasts of lettuce grown under field conditions. An average membrane area of 500 microns 2 for the thylakoids in a chloroplast was obtained from the surface density and the average volume of the chloroplasts (11.6 microns 3, estimated by means of equivalent oblate spheroids). The advantage of the morphometric method over alternative techniques and the relevance of the results with respect to the topology of thylakoid membranes are discussed.