Photoreceptor death: Spatiotemporal patterns arising from one-hit death kinetics and a diffusible cell death factor

Retinitis pigmentosa (RP) is an inherited disease affecting approximately 1: 4000 individuals in North America. It is characterized clinically by the gradual apoptotic death of photoreceptor cells that occurs nonuniformly across the surface of the retina. Recently, it has been demonstrated that the time of death of many individual photoreceptors is random, a fact that must be reconciled with the spatiotemporal patterns of photoreceptor degeneration that are observed in patients with RP. One possible explanation is that a diffusible toxic factor is released by dying photoreceptors and induces adjacent cells to likewise undergo apoptosis. To determine if such a mechanism can result in patchy distributions of photoreceptor death, as frequently observed in RP patients, we studied cell attrition produced by a bistable biochemical switch in an idealized one-dimensional retina. We found that with a reasonable choice of parameter values, our model was able to produce patterns of cell death resembling those observed in RP. In the context of this model, patches on the order of histologically observable size could develop from a single release event, but their rates of formation were independent of the concentration of toxic factor released. Instead, factor concentration affected the overall rate of cell death, the number of degenerating patches, and their distribution across the retina.     

Reptin and pontin antagonistically regulate heart growth in zebrafish embryos

Organ size is precisely regulated during development, but the control mechanisms remain obscure. We have isolated a mutation in zebrafish, liebeskummer (lik), which causes development of hyperplastic embryonic hearts. lik encodes Reptin, a component of a DNA-stimulated ATPase complex. The mutation activates ATPase activity of Reptin complexes and causes a cell-autonomous proliferation of cardiomyocytes to begin well after progenitors have fashioned the primitive heart tube. With regard to heart growth, beta-catenin and Pontin, a DNA-stimulated ATPase that is often part of complexes with Reptin, are in the same genetic pathways. Pontin reduction phenocopies the cardiac hyperplasia of the lik mutation. Thus, the Reptin/Pontin ratio serves to regulate heart growth during development, at least in part via the beta-catenin pathway.     

Pulmonary type II cell hypertrophy and pulmonary lipoproteinosis are features of chronic IL-13 exposure

Interleukin (IL)-13, a key mediator of Th2-mediated immunity, contributes to the pathogenesis of asthma and other pulmonary diseases via its ability to generate fibrosis, mucus metaplasia, eosinophilic inflammation, and airway hyperresponsiveness. In these studies, we compared surfactant accumulation in wild-type mice and mice in which IL-13 was overexpressed in the lung. When compared with littermate controls, transgenic animals showed alveolar type II cell hypertrophy under light and electron microscopy. Over time, their alveoli also filled with surfactant in a pulmonary alveolar proteinosis pattern. At the same time, prominent interstitial fibrosis occurs. Bronchoalveolar lavage fluid from these mice had a three- to sixfold increase in surfactant phospholipids. Surfactant proteins (SP)-A, -B, and -C showed two- to threefold increases, whereas SP-D increased 70-fold. These results indicate that IL-13 is a potent stimulator of surfactant phospholipid and surfactant accumulation in the lung. IL-13 may therefore play a central role in the broad range of chronic pulmonary conditions in which fibrosis, type II cell hypertrophy, and surfactant accumulation occur.     

Manipulation of immune responses to Mycobacterium bovis by vaccination with IL-2- and IL-18-secreting recombinant bacillus Calmette Guerin

Bacillus Calmette Guerin (BCG) has been reported to show variable efficacy as a vaccine against tuberculosis. We demonstrated that the secretion of biologically active IL-2 (rBCG/IL-2),but not IL-18 (rBCG/IL-18), by BCG improves its ability to induce and maintain a strong type 1 immune response in BALB/c mice. rBCG/IL-2 induced significantly higher Ag-specific proliferative responses, high IFN-gamma production and serum titres of IgG2a 16 weeks after vaccination. This immune profile was correlated to an increased rate of clearance of non-pathogenic mycobacteria (live BCG delivered intranasally). Surprisingly, however,this strong type 1 immune profile induced no greater protective immunity against aerosol challenge with virulent Mycobacterium bovis than that induced by normal BCG (nBCG). By comparison,vaccination with rBCG/IL-18 was found to induce significantly less IFN-gamma production in splenic lymphocytes than nBCG.This impaired induction of IFN-gamma was correlated to a significantly lower protective efficacy against M. bovis challenge, as compared to nBCG. The data suggest that manipulation of the immune response to tuberculosis and tuberculosis vaccines will require a more complete understanding of the factors that are important in generating a protective immune response.     

Spatial and temporal analysis of the microbial community in slow sand filters used for treating horticultural irrigation water

An experimental slow sand filter (SSF) was constructed to study the spatial and temporal structure of a bacterial community suppressive to an oomycete plant pathogen, Phytophthora cryptogea. Passage of water through the mature sand column resulted in complete removal of zoospores of the plant pathogen. To monitor global changes in the microbial community, bacterial and fungal numbers were estimated on selective media, direct viable counts of fungal spores were made, and the ATP content was measured. PCR amplification of 16S rRNA genes and denaturing gradient gel electrophoresis (DGGE) were used to study the dynamics of the bacterial community in detail. The top layer (1 cm) of the SSF column was dominated by a variable and active microbial population, whereas the middle (50 cm) and bottom (80 cm) layers were dominated by less active and diverse bacterial populations. The major changes in the microbial populations occurred during the first week of filter operation, and these populations then remained to the end of the study. Spatial and temporal nonlinear mapping of the DGGE bands provided a useful visual representation of the similarities between SSF samples. According to the DGGE profile, less than 2% of the dominating bands present in the SSF column were represented in the culturable population. Sequence analysis of DGGE bands from all depths of the SSF column indicated that a range of bacteria were present, with 16S rRNA gene sequences similar to groups such as Bacillus megaterium, Cytophaga, Desulfovibrio, Legionella, Rhodococcus rhodochrous, Sphingomonas, and an uncharacterized environmental clone. This study describes the characterization of the performance, and microbial composition, of SSFs used for the treatment of water for use in the horticultural industry. Utilization of naturally suppressive population of microorganisms either directly or by manipulation of the environment in an SSF may provide a more reproducible control method for the future.     

Some possible codes for encrypting data in DNA

Three codes are reported for storing written information in DNA. We refer to these codes as the Huffman code, the comma code and the alternating code. The Huffman code was devised using Huffman's algorithm for constructing economical codes. The comma code uses a single base to punctuate the message, creating an automatic reading frame and DNA which is obviously artificial. The alternating code comprises an alternating sequence of purines and pyrimidines, again creating DNA that is clearly artificial. The Huffman code would be useful for routine, short-term storage purposes, supposing – not unrealistically – that very fast methods for assembling and sequencing large pieces of DNA can be developed. The other two codes would be better suited to archiving data over long periods of time (hundreds to thousands of years).     

Induction of cyclooxygenase 2 by Escherichia coli but not Helicobacter pylori lipopolysaccharide in gastric epithelial cells in vitro

Background. Cyclooxygenase 2 (COX‐2) is an inducible enzyme that plays a key role in the synthesis of prostaglandins in response to inflammatory stimuli. It is expressed in the gastric mucosa as part of the response to infection with Helicobacter pylori. The specific interaction between H. pylori and the gastric epithelium that results in COX‐2 expression has not been identified. Methods. In order to investigate the hypothesis that lipopolysaccharide (LPS) from H. pylori plays a role in the induction of cyclooxygenase 2 in the stomach, gastric cell lines MKN‐7 and MKN‐45 were incubated with LPS from either H. pylori NCTC 11637 or Escherichia coli 055:B5. Incubation of cells with live H. pylori NCTC 11637 was also carried out as a positive control. Cells were then analysed for COX‐2 protein and mRNA and prostaglandin E2 synthesis. Results. Cyclooxygenase 2 protein and mRNA expression was induced by E. coli LPS and live H. pylori, but not by H. pylori LPS. Prostaglandin E₂ synthesis increased in a dose‐dependent manner in both cell lines with E. coli but not H. pylori LPS. Conclusions. H. pylori LPS is of low biological activity when compared with E. coli LPS in its ability to induce the expression of cyclooxygenase 2 and synthesis of prostaglandin E₂. This may provide one mechanism by which H. pylori minimizes the inflammatory response in the gastric mucosa, allowing chronic infection.