Cellular FLICE-inhibitory protein (cFLIP) isoforms block CD95- and TRAIL death receptor-induced gene induction irrespective of processing of caspase-8 or cFLIP in the death-inducing signaling complex

Death receptors (DRs) induce apoptosis but also stimulate proinflammatory "non-apoptotic" signaling (e.g. NF-κB and mitogen-activated protein kinase (MAPK) activation) and inhibit distinct steps of DR-activated maturation of procaspase-8. To examine whether isoforms of cellular FLIP (cFLIP) or its cleavage products differentially regulate DR signaling, we established HaCaT cells expressing cFLIP(S), cFLIP(L), or mutants of cFLIP(L) (cFLIP(D376N) and cFLIP(p43)). cFLIP variants blocked TRAIL- and CD95L-induced apoptosis, but the cleavage pattern of caspase-8 in the death inducing signaling complex was different: cFLIP(L) induced processing of caspase-8 to the p43/41 fragments irrespective of cFLIP cleavage. cFLIP(S) or cFLIP(p43) blocked procaspase-8 cleavage. Analyzing non-apoptotic signaling pathways, we found that TRAIL and CD95L activate JNK and p38 within 15 min. cFLIP variants and different caspase inhibitors blocked late death ligand-induced JNK or p38 MAPK activation suggesting that these responses are secondary to cell death. cFLIP isoforms/mutants also blocked death ligand-mediated gene induction of CXCL-8 (IL-8). Knockdown of caspase-8 fully suppressed apoptotic and non-apoptotic signaling. Knockdown of cFLIP isoforms in primary human keratinocytes enhanced CD95L- and TRAIL-induced NF-κB activation, and JNK and p38 activation, underscoring the regulatory role of cFLIP for these DR-mediated signals. Whereas the presence of caspase-8 is critical for apoptotic and non-apoptotic signaling, cFLIP isoforms are potent inhibitors of TRAIL- and CD95L-induced apoptosis, NF-κB activation, and the late JNK and p38 MAPK activation. cFLIP-mediated inhibition of CD95 and TRAIL DR could be of crucial importance during keratinocyte skin carcinogenesis and for the activation of innate and/or adaptive immune responses triggered by DR activation in the skin.     

The cross-correlation and phase-difference methods are not equivalent under noninvasive estimation of the motor unit propagation velocity.

Noninvasive estimation of motor unit propagation velocity (MUPV) was reduced to that of the time delay between signals detected by two surface EMG electrodes placed along the muscle fibres. When the cross-correlation function between the signals was used, the problem with temporal resolution arose. Estimation of the time delay in the frequency domain was proposed to overcome this problem. To check whether the cross-correlation and phase-difference methods give the same estimates, the results obtained by both methods were compared through simulation. A different sensitivity of the two methods to the effects of the excitation origin and extinction was found. Besides, the quality of the estimate depended on the electrode arrangement. The longitudinal double difference electrodes were preferable with the phase-difference method, while the MUPV estimates obtained by the cross-correlation technique were more correct when the longitudinal single difference or bipolar transversal double difference electrodes were used. In addition, the estimates obtained by the phase-difference method were more sensitive to the longitudinal scattering of motor end-plates and ends of the fibres, to the fibre lengths and to the negative after-potential magnitude. Such sensitivity could make MUPV estimates incorrect even under a relatively small distance between the motor unit axis and electrode.     

Karyotype constancy and genome size variation in BulgarianCrepis foetida s. l. (Asteraceae)

Ten populations ofCrepis foetida from Bulgaria belonging to the three subspeciesfoetida, rhoeadifolia, andcommutata were analyzed karyologically using haematoxylin staining, Giemsa C-banding, fluorochrome banding, Ag-NOR staining, Feulgen cytophotometry (scanning densitometry and video-based image analysis), and propidium iodide flow cytometry. The quantitatively-evaluated karyotype structure was similar among all populations, with minor variation in a few intercalary sites only and in the amount of NOR-associated heterochromatin (satellites). In contrast to the karyotypic constancy the genome size ofC. foetida subsp.commutata was about 10% lower than those of the other two subspecies, which had similar genome sizes. The genome size measurements using three different methods resulted in highly correlated data. The genome size difference adds some weight to previous taxonomic opinions treatingC. foetida subsp.commutata at species level, asC. commutata. Prof. Dr. Stefan Kozhuharov (4 January 1933–24 August 1997).     

Mathematical modelling of intra- and extracellular potentials generated by active structures with short regions of increased diameter

The Hodgkin-Huxley (1952) model was used to calculate intracellular potentials by the method of Joyner et al. (1978). Extracellular potentials were estimated on the basis of a mathematical model proposed by us. It has shown that, irrespective of practical isopotentiality of the membrane of a local inhomogeneity, the latter affects extracellular potentials in two ways: 1) through changes in the potential profile in the region of the structure before the inhomogeneity; 2) through its own potential profile. The first effect is considerably greater than the second one, but the second is greater than the effect of the equal portion of the thin fibre. Increase in the diameter or length of an inhomogeneity is combined with such changes in the potential profile, that the effect of the inhomogeneity on the extracellular potential amplitude is practically independent of its actual size. The extracellular potential waveform substantially depends on the ratio of the diameters of the two parts of the structure and on the position of the inhomogeneity in relation to the sealed structure end. Registration of the positive-negative potentials having a large positive phase should not be considered as an indication of passive properties of the structure.     

Chromaticity in the UV/blue range facilitates the search for achromatically background-matching prey in birds

A large variety of predatory species rely on their visual abilities to locate their prey. However, the search for prey may be hampered by prey camouflage. The most prominent example of concealing coloration is background-matching prey coloration characterized by a strong visual resemblance of prey to the background. Even though this principle of camouflage was recognized to efficiently work in predator avoidance a long time ago, the underlying mechanisms are not very well known. In this study, we assessed whether blue tits (Cyanistes caeruleus) use chromatic cues in the search for prey. We used two prey types that were achromatically identical but differed in chromatic properties in the UV/blue range and presented them on two achromatically identical backgrounds. The backgrounds had either the same chromatic properties as the prey items (matching combination) or differed in their chromatic properties (mismatching combination). Our results show that birds use chromatic cues in the search for mismatching prey, whereupon chromatic contrast leads to a ‘pop-out’ of the prey item from the background. When prey was presented on a matching background, search times were significantly higher. Interestingly, search for more chromatic prey on the matching background was easier than search for less chromatic prey on the matching background. Our results indicate that birds use both achromatic and chromatic cues when searching for prey, and that the combination of both cues might be helpful in the search task.     

Receptor for activated C kinase 1 stimulates nascent polypeptide-dependent translation arrest

Nascent peptide-dependent translation arrest is crucial for the quality control of eukaryotic gene expression. Here we show that the receptor for activated C kinase 1 (RACK1) participates in nascent peptide-dependent translation arrest, and that its binding to the 40S subunit is crucial for this. Translation arrest by a nascent peptide results in Dom34/Hbs1-independent endonucleolytic cleavage of mRNA, and this is stimulated by RACK1. We propose that RACK1 stimulates the translation arrest that is induced by basic amino-acid sequences that leads to endonucleolytic cleavage of the mRNA, as well as to co-translational protein degradation.