Cancer and stem cell biology: how tightly intertwined?

Ever since the discovery of cancer stem cells in leukemia and, more recently, in solid tumors, enormous attention has been paid to the apparent stem cell nature of cancer. These concepts were the focus of the "Stem Cells and Cancer" symposium held recently at the University of California, San Francisco, and the inspiration for this overview of current research and important questions emerging in this area.     

Cicada acoustic communication: potential sound partitioning in a multispecies community from Mexico (Hemiptera: Cicadomorpha: Cicadidae)

Multispecies cicada communities in neotropical rainforests produce a complex and intense acoustic environment. In a fragment of a Mexican rainforest (Veracruz, Mexico), a cicada community at the end of the dry season consisted of nine species ( Daza montezuma; Pacarina schumanni; Miranha imbellis; Dorisiana sutori; Fidicinoides picea; Fidicinoides pronoe; Quesada gigas; one species of the genus Neocicada and one uncaught canopy species). Seven of the nine species formed dense choruses at dawn and at dusk. Each species showed preferences in the height of calling sites. Males of the species were solitary or gregarious, and followed a 'call-fly' or a 'call-stay' calling strategy. Acoustic signals of each species had particular time and frequency patterns. All these specific features appear to separate the nine species acoustically and lead to a partitioning of the acoustic environment. The acoustic partitioning might decrease the risk of heterospecific courting and mating.© 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 379–394.     

Linear 2′ O-Methyl RNA probes for the visualization of RNA in living cells

U1snRNA, U3snRNA, 28 S ribosomal RNA, poly(A) RNA and a specific messenger RNA were visualized in living cells with microinjected fluorochrome-labeled 2′ O-Methyl oligoribonucleotides (2′ OMe RNA). Antisense 2′ OMe RNA probes showed fast hybridization kinetics, whereas conventional oligodeoxyribonucleotide (DNA) probes did not. The nuclear distributions of the signals in living cells were similar to those found in fixed cells, indicating specific hybridization. Cytoplasmic ribosomal RNA, poly(A) RNA and mRNA could hardly be visualized, mainly due to a rapid entrapment of the injected probes in the nucleus. The performance of linear probes was compared with that of molecular beacons, which due to their structure should theoretically fluoresce only upon hybridization. No improvements were achieved however with the molecular beacons used in this study, suggesting opening of the beacons by mechanisms other than hybridization. The results show that linear 2′ OMe RNA probes are well suited for RNA detection in living cells, and that these probes can be applied for dynamic studies of highly abundant nuclear RNA. Furthermore, it proved feasible to combine RNA detection with that of green fluorescent protein-labeled proteins in living cells. This was applied to show co-localization of RNA with proteins and should enable RNA–protein interaction studies.     

Wing cross veins: an efficient biomechanical strategy to mitigate fatigue failure of insect cuticle

Locust wings are able to sustain millions of cycles of mechanical loading during the lifetime of the insect. Previous studies have shown that cross veins play an important role in delaying crack propagation in the wings. Do cross veins thus also influence the fatigue behaviour of the wings? Since many important fatigue parameters are not experimentally accessible in a small biological sample, here we use the finite element (FE) method to address this question numerically. Our FE model combines a linear elastic material model, a direct cyclic approach and the Paris law and shows results which are in very good agreement with previously reported experimental data. The obtained results of our study show that cross veins indeed enhance the durability of the wings by temporarily stopping cracks. The cross veins further distribute the stress over a larger area and therefore minimize stress concentrations. In addition, our work indicates that locust hind wings have an endurance limit of about 40% of the ultimate tensile strength of the wing material, which is comparable to many engineering materials. The comparison of the results of the computational study with predictions of two most commonly used fatigue failure criteria further indicates that the Goodman criterion can be used to roughly predict the failure of the insect wing. The methodological framework presented in our study could provide a basis for future research on fatigue of insect cuticle and other biological composite structures.     

Localization of phosphoserine residues in the alpha subunit of rabbit skeletal muscle phosphorylase kinase

The alpha subunit of skeletal muscle phosphorylase kinase, as isolated, carries phosphate at the serine residues 1018, 1020 and 1023. Employing the S-ethyl-cysteine method, these residues are found to be phosphorylated partially, i.e. differently phosphorylated species exist in muscle. Serine 1018 is a site which can be phosphorylated by the cyclic-AMP-dependent protein kinase. The serine residues 972, 985 and 1007 are phosphorylated by phosphorylase kinase itself when its activity is stimulated by micromolar concentrations of Ca2+. These phosphorylation sites are not identical to those found to be phosphorylated already in the enzyme as prepared from freshly excised muscle. A 'multiphosphorylation loop' uniquely present in this but not in the homologous beta subunit contains all the phosphoserine residues so far identified in the alpha subunit.     

Age-Associated Impairments in Mitochondrial ADP Sensitivity Contribute to Redox Stress in Senescent Human Skeletal Muscle

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