The impact of cyclin-dependent kinase 5 depletion on poly(ADP-ribose) polymerase activity and responses to radiation

Cyclin-dependent kinase 5 (Cdk5) has been identified as a determinant of sensitivity to poly(ADP-ribose) polymerase (PARP) inhibitors. Here, the consequences of its depletion on cell survival, PARP activity, the recruitment of base excision repair (BER) proteins to DNA damage sites, and overall DNA single-strand break (SSB) repair were investigated using isogenic HeLa stably depleted (KD) and Control cell lines. Synthetic lethality achieved by disrupting PARP activity in Cdk5-deficient cells was confirmed, and the Cdk5^KD cells were also found to be sensitive to the killing effects of ionizing radiation (IR) but not methyl methanesulfonate or neocarzinostatin. The recruitment profiles of GFP-PARP-1 and XRCC1-YFP to sites of micro-irradiated Cdk5^KD cells were slower and reached lower maximum values, while the profile of GFP-PCNA recruitment was faster and attained higher maximum values compared to Control cells. Higher basal, IR, and hydrogen peroxide-induced polymer levels were observed in Cdk5^KD compared to Control cells. Recruitment of GFP-PARP-1 in which serines 782, 785, and 786, potential Cdk5 phosphorylation targets, were mutated to alanines in micro-irradiated Control cells was also reduced. We hypothesize that Cdk5-dependent PARP-1 phosphorylation on one or more of these serines results in an attenuation of its ribosylating activity facilitating persistence at DNA damage sites. Despite these deficiencies, Cdk5^KD cells are able to effectively repair SSBs probably via the long patch BER pathway, suggesting that the enhanced radiation sensitivity of Cdk5^KD cells is due to a role of Cdk5 in other pathways or the altered polymer levels.     

How to (properly) strengthen Bell's theorem using counterfactuals

Bell's theorem in its standard version demonstrates that the joint assumptions of the hidden-variable hypothesis and the principle of local causation lead to a conflict with quantum-mechanical predictions. In his latest counterfactual strengthening of Bell's theorem, Stapp attempts to prove that the locality assumption itself contradicts the quantum-mechanical predictions in the Hardy case. His method relies on constructing a complex, non-truth functional formula which consists of statements about measurements and outcomes in some region R, and whose truth value depends on the selection of a measurement setting in a space-like separated location L. Stapp argues that this fact shows that the information about the measurement selection made in L has to be present in R. I give detailed reasons why this conclusion can and should be resisted. Next I correct and formalize an informal argument by Shimony and Stein showing that the locality condition coupled with Einstein's criterion of reality is inconsistent with quantum-mechanical predictions. I discuss the possibility of avoiding the inconsistency by rejecting Einstein's criterion rather than the locality assumption.     

The proteasome antechamber maintains substrates in an unfolded state

Eukaryotes and archaea use a protease called the proteasome that has an integral role in maintaining cellular function through the selective degradation of proteins. Proteolysis occurs in a barrel-shaped 20S core particle, which in Thermoplasma acidophilum is built from four stacked homoheptameric rings of subunits, α and β, arranged α(7)β(7)β(7)α(7) (ref. 5). These rings form three interconnected cavities, including a pair of antechambers (formed by α(7)β(7)) through which substrates are passed before degradation and a catalytic chamber (β(7)β(7)) where the peptide-bond hydrolysis reaction occurs. Although it is clear that substrates must be unfolded to enter through narrow, gated passageways (13?? in diameter) located on the α-rings, the structural and dynamical properties of substrates inside the proteasome antechamber remain unclear. Confinement in the antechamber might be expected to promote folding and thus impede proteolysis. Here we investigate the folding, stability and dynamics of three small protein substrates in the antechamber by methyl transverse-relaxation-optimized NMR spectroscopy. We show that these substrates interact actively with the antechamber walls and have drastically altered kinetic and equilibrium properties that maintain them in unstructured states so as to be accessible for hydrolysis.     

An imperfect imago? Post-mating loss of iridescent scales in Cheimas butterflies may change female from attractive to cryptic (Lepidoptera: Nymphalidae: Satyrinae)

Adults of both sexes of Cheimas opalinus (Staudinger), a Satyrinae butterfly occurring in the cloud forests of the Venezuelan Cordillera de Mérida, have simple wing colour patterns, dark brown dorsa marked by one conspicuous element, large greenish-blue patches in the discal area of the hind wing. It was observed that in young, freshly emerged females these patches are frequently absent. They fade away and eventually disappear during mating and nuptial flights when brushed out by lateral movements of the male’s hind wing put between folded female hind wings. The falling off of the scales is made easy because they do not adhere to the wing as firmly as brown background scales due to their particular folded extremities. We speculate that this process is related to the fitness of the females. Prior to mating, blue-green patches are advantageous because they attract the attention of the opposite sex and enhance the chances of successful mating. After mating they lose their sexual role. Females without the blue-green patches become cryptic. Thus, they are less apparent not only for the males, which helps them avoid sexual harassment, but also for potential bird predators. Additionally, the loss of blue reflecting scales may speed up the warming up of the abdomen and egg maturation. In the males, positive role of the patches (signalling), and negative (bird attraction), is balanced during their entire life span, and they fade gradually due to regular usage of wings scaling in flight. Our hypothesis is supported by morphological, optical, experimental and statistical analysis in which we used 509 individuals of both sexes. A similar ratio of young (with undamaged wing) females with or without blue patch was recorded, whereas in the males no individuals without any trace of blue patch were reported, and a correlation of age (wing damage) and gradual fading off of the patch was demonstrated. Such an adaptation involving an active change of the appearance of adults, i.e. colour patterns related to sexual selection, has not been reported previously in Lepidoptera.     

Pre-ovipositional and ovipositional behaviour of Trichouropoda ovalis (C.L. Koch) and Uroobovella marginata (C.L. Koch) (Parasitiformes: Uropodina: Trematuridae,Urodinychidae) with notes on egg incubation and hatching behaviour

Egg deposition by the soil mites Trichouropoda (= Oodinychus) ovalis (C.L. Koch and Uroobovella (= Fuscuropoda) marginata (C.L. Koch), egg incubation and hatching behaviour were observed using continuous video-monitoring. The oviposition in both species was found to consist of three distinct phases. In Phase 1, both species engage in pre-ovipositional activity prior to the egg being extruded from the genital opening. Phase 1 lasted approximately 7.5 minutes in T. ovalis and about 6 minutes in U. marginata. Phase 2 involved egg deposition and lasted approximately 2.5 times longer in T. ovalis (88 seconds) than in U. marginata. Egg covering occurs in Phase 3, and in both species lasts about 25 minutes. Incubation time in U. marginata (137 hours) was approximately 30% shorter compared to that of T. ovalis, while the hatching time was 2 times longer (150 min) in the latter species.