The evolutionary emergence of stochastic phenotype switching in bacteria

Stochastic phenotype switching - or bet hedging - is a pervasive feature of living systems and common in bacteria that experience fluctuating (unpredictable) environmental conditions. Under such conditions, the capacity to generate variable offspring spreads the risk of being maladapted in the present environment, against offspring likely to have some chance of survival in the future. While a rich subject for theoretical studies, little is known about the selective causes responsible for the evolutionary emergence of stochastic phenotype switching. Here we review recent work - both theoretical and experimental - that sheds light on ecological factors that favour switching types over non-switching types. Of particular relevance is an experiment that provided evidence for an adaptive origin of stochastic phenotype switching by subjecting bacterial populations to a selective regime that mimicked essential features of the host immune response. Central to the emergence of switching types was frequent imposition of 'exclusion rules' and 'population bottlenecks' - two complementary faces of frequency dependent selection. While features of the immune response, exclusion rules and bottlenecks are likely to operate in many natural environments. Together these factors define a set of selective conditions relevant to the evolution of stochastic switching, including antigenic variation and bacterial persistence.     

Scats and den contents as indicators of the diet of stoats (Mustela erminea) in the Tasman Valley,South Canterbury,New Zealand

Stoats are significant predators of native fauna in New Zealand. They occur in many habitat types and consume a wide range of prey. The diet of stoats in the Tasman River, South Canterbury, was studied by analysis of scats and den contents. Analysis of 206 scats showed that stoats ate mainly lagomorphs, birds and invertebrates. Minor components included mice, lizards, fish and hedgehogs. Stoats ate more birds in spring than in autumn, and female stoats ate more invertebrates than did males. The contents of 219 dens collected in the same area at the same time provided further information. Birds and lagomorphs occurred at high frequency in dens, and other components were minor. Remains in dens were larger than in scats and allowed identification of many more prey items to species level. Den contents revealed a potentially substantial impact of stoats on threatened shorebirds locally; this impact was not detected by analysis of scats.     

Expression of Claudins and Their Prognostic Significance in Noninvasive Urothelial Neoplasms of the Human Urinary Bladder

The members of the claudin family are major integral transmembrane protein constituents of tight junctions. Normal and neoplastic tissues can be characterized by unique qualitative and quantitative distribution of claudin subtypes, which may be related to clinicopathological features. Differential diagnosis and prognosis of nonmuscle invasive tumor entities of urinary bladder epithelium are often challenging. The aim was to investigate the expression profile of claudins in inverted urothelial papillomas (IUPs), urothelial papillomas (UPs), papillary urothelial neoplasms of low malignant potential (PUNLMPs), and intraepithelial (Ta), low-grade urothelial cell carcinomas (LG-UCCs) in order to reveal potential prognostic and differential diagnostic values of certain claudins. Claudin-1, -2, -4, and -7 protein expressions detected by immunohistochemistry and clinical data were analyzed in 15 IUPs, 20 UPs, 20 PUNLMPs, and 20 LG-UCCs. UPs, PUNLMPs, and LG-UCCs showed significantly decreased claudin-1 expression in comparison to IUPs. LG-UCCs expressing claudin-4 over the median were associated with significantly shorter recurrence-free survival. PUNLMPs expressing claudin-1 over the median revealed significantly longer recurrence-free survival. High claudin-1 protein expression might help to differentiate IUP from UPs, PUNLMPs, and LG-UCCs. High claudin-4 expression may determine an unfavorable clinical course of LG-UCCs, while high claudin-1 expression in PUNLMP was associated with markedly better clinical outcome.     

Hepatocarcinogenesis in human liver

Due to the development of the imaging techniques and liver surgery, pathologists are encountered more frequently with preneoplastic liver lesions. Well-defined stages of human hepatocarcinogenesis have been distinguished recently. Dysplastic foci represent the earliest stage of this process. Small-cell dysplastic foci are tumor precursors, but the large-cell form of this lesion does not progress further. The next stage is the dysplastic nodule, this larger lesion can be recognized by imaging techniques and gross examination of the specimen. Low- and high-risk forms are distinguished based on the level of cytological and structural atypia. The small hepatocellular carcinomas have a diameter of less than 2 cm by definition. The small HCC of indistinctly nodular type is equivalent of in situ carcinomas in other organs and designated sometimes as early HCC. The small HCC of the distinctly nodular type can be interpreted as advanced cancer despite its small size. The distinction between these lesions can be facilitated by ancillary techniques. The so-called capillarization of the liver sinusoids during the progression is characterized by the increased expression of endothelial markers as CD31 and CD34. Immunostaining for CD44, beta-catenin and p53 has prognostic value. Molecular biological techniques reveal gradual epigenetic and DNA changes during the process of hepatocarcinogenesis. Global gene expression profiling of hepatocellular carcinomas may result in a new classification of this tumor and can reveal new potential therapeutic targets.     

Hepatitis viruses and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is among the most frequent malignancies worldwide. Hepatitis viruses, such as the hepatitis B virus (HBV) and hepatitis C virus (HCV) are undoubtedly listed in the etiology of HCC. Studies show that, in the near future, viral hepatitis will carry increasing weight in the etiology of HCC. This review briefly discusses the known carcinogenic effects of HBV and HCV in the light of experimental and human studies. The data show that viral proteins may directly interfere with gene products responsible for cell proliferation and cell growth. Many other signal transduction cascades may be affected as well. Direct integration of HBV viral sequences into the host genome increases the genomic instability. The genomic imbalance allows the development and survival of malignant clones bearing defected genomic information. HBV and HCV infection induces indirect and direct mechanisms through cellular damage, increased regeneration and cell proliferation, therefore enhancing the development of HCC.     

Orientational behavior of phosphatidylcholine bilayers in the presence of aromatic amphiphiles and a magnetic field.

A number of aromatic-containing additives which can influence the orientation of fragments of lipid bilayer membranes by a magnetic field have been investigated. Two properties of these additives prove important: (1) sufficient detergency to facilitate reorganization of bilayer components and (2), sufficient anisotropy in magnetic susceptibility the preferred direction of fragment orientation. Triton X-100 is identified as effective in terms of facilitating magnetic field ordering of bilayer fragments but does not alter the preferred direction of orientation. A combination of the detergent CHAPSO (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate) and the aromatic alcohol 1-naphthol facilitates both ordering and alters the preferred direction of bilayer orientation. As mixtures of dimyristoylphosphatidylcholine (DMPC) and CHAPSO, which orient with bilayer normals perpendicular to the magnetic field, were titrated with 1-naphthol, the assemblies underwent transitions, first to random orientation, and then to an orientation with bilayer normals parallel to the field. Based on temperature-induced phase transitions and the extent of motional averaging of the 31P shielding tensor of the DMPC headgroup, the DMPC in these oriented samples appears to maintain a bilayer morphology during transitions. The insight provided in this study regarding factors which influence fragment stability and orientation lays the groundwork for the design of improved field-oriented media for spectroscopic investigation of membrane components.     

Synthesis of [H]- and -[C]-labelled sulprostone (CP-34,089/ZK-57,671)

The synthesis of N-methanesulfonyl 16-phenoxy-ω-tetranor PGE₂ carboxamide (sulprostone — CP-34,089/ZK-57,671) labeled with tritium and carbon-14 is described. Sulprostone labeled with tritium in the phenoxy moiety by means of catalytic hydrogenolysis was obtained in a 17% radiochemical yield with a specific activity of 1.0 Ci/mmol. The methanesulfonamide-¹⁴C derivative of sulprostone was prepared from methyl-¹⁴C iodide in an 11.8% radiochemical yield having a specific activity of 18.8 mCi/mmol.