When colour patterns reflect phylogeography: New species of Dasypeltis (Serpentes: Colubridae: Boigini) from West Africa

Six colour phases are currently known in the genus Dasypeltis in West Africa, three in the D. scabra complex and three in the D. fasciata complex. Molecular phylogenetic analysis reveals that all correspond to distinct species. D. parascabra sp. nov. is described from wet savannah areas of Guinea and Ivory Coast. D. latericia is given full specific rank. The validity of D. sahelensis, D. gansi and D. confusa – three species recently described on the basis of colour pattern and biogeography – is confirmed. D. fasciata is confined to rain forest areas of West and Central Africa. D. scabra is absent from West Africa.     

Field-dependent effect of crown ether (18-crown-6) on ionic conductance of alpha-hemolysin channels

Closing linear poly(ethylene glycol) (PEG) into a circular "crown" dramatically changes its dynamics in the alpha-hemolysin channel. In the electrically neutral crown ether (C2H4O)6, six ethylene oxide monomers are linked into a circle that gives the molecule ion-complexing capacity and increases its rigidity. As with linear PEG, addition of the crown to the membrane-bathing solution decreases the ionic conductance of the channel and generates additional conductance noise. However, in contrast to linear PEG, both the conductance reduction (reporting on crown partitioning into the channel pore) and the noise (reporting on crown dynamics in the pore) now depend on voltage strongly and nonmonotonically. Within the whole frequency range accessible in channel reconstitution experiments, the noise power spectrum is "white", showing that crown exchange between the channel and the bulk solution is fast. Analyzing these data in the framework of a Markovian two-state model, we are able to characterize the process quantitatively. We show that the lifetime of the crown in the channel reaches its maximum (a few microseconds) at about the same voltage (approximately 100 mV, negative from the side of protein addition) where the crown's reduction of the channel conductance is most pronounced. Our interpretation is that, because of its rigidity, the crown feels an effective steric barrier in the narrowest part of the channel pore. This barrier together with crown-ion complexing and resultant interaction with the applied field leads to behavior usually associated with voltage-dependent binding in the channel pore.     

Characterization of a new hybrid mink-mouse clone panel: chromosomal and regional assignments of the GLO,ACY, NP,CKBB, ADH2, and ME1 loci in mink (Mustela vison)

To expand the mink map, we established a new panel consisting of 23 mink-mouse clones. On the basis of statistical criteria (Wijnen et al. 1977; Burgerhout 1978), we developed a computer program for choice of clones of the panel. Assignments of the following mink genes were achieved with the use of the hybrid panel: glyoxalase (GLO), Chromosome (Chr) 1; acetyl acylase (ACY), Chr 5; creatine phosphokinase B (CKBB), Chr 10; alcohol dehydrogenase-2 (subunit B) (ADH2), Chr 8. Using a series of clones carrying rearrangements involving mink Chr 1 and 8, we assigned the gene for ME1 to the short arm of Chr 1 and that for ADH2 to Chr 8, in the region 8p12-p24. Mapping results confirm the ones we previously obtained with a mink-Chinese hamster panel. However, by means of an improved electrophoretic technique, we revised the localization of the gene for purine nucleoside phosphorylase (NP), which has been thought to be on mink Chr 2. It is reassigned to mink Chr 10.     

Targeted genomic integration of EGFP under tubulin beta 3 class III promoter and mEos2 under tryptophan hydroxylase 2 promoter does not produce sufficient levels of reporter gene expression

Neuronal tracing is a modern technology that is based on the expression of fluorescent proteins under the control of cell type–specific promoters. However, random genomic integration of the reporter construct often leads to incorrect spatial and temporal expression of the marker protein. Targeted integration (or knock-in) of the reporter coding sequence is supposed to provide better expression control by exploiting endogenous regulatory elements. Here we describe the generation of two fluorescent reporter systems: enhanced green fluorescent protein (EGFP) under pan-neural marker class III β-tubulin (Tubb3) promoter and mEos2 under serotonergic neuron-specific tryptophan hydroxylase 2 (Tph2) promoter. Differentiation of Tubb3-EGFP embryonic stem (ES) cells into neurons revealed that though Tubb3-positive cells express EGFP, its expression level is not sufficient for the neuronal tracing by routine fluorescent microscopy. Similarly, the expression levels of mEos2-TPH2 in differentiated ES cells was very low and could be detected only on messenger RNA level using polymerase chain reaction-based methods. Our data shows that the use of endogenous regulatory elements to control transgene expression is not always beneficial compared with the random genomic integration.     

Marker-Dependent Recombination in T4 Bacteriophage. I. Outline of the Phenomenon and Evidence Suggesting a Mismatch Repair Mechanism

In standard crosses, some rIIB mutants of T4 phage were found to be susceptible to an extra recombination mechanism to which the other mutants were much less susceptible. The following observations were interpreted as evidence for the mismatch-repair nature of the phenomenon: (1) Marker-dependent recombination generates exclusively double exchanges at both sides of the marker. (2) Marker-dependent recombination is highly sensitive to DNA base sequence at the site of the marker and to that at the corresponding site on the chromosome of the other parent. (3) Within certain limits, the contribution of the marker-dependent mechanism to the total recombination frequency is distance-independent and thus constitutes a constant component.     

Short-term partitioning of Cd recently taken up between sunflowers organs (<Emphasis Type="Italic">Helianthus annuus</Emphasis>) at flowering and grain filling stages: effect of plant transpiration and allometry

Aims

This work concentrated on understanding the allocation of Cd recently taken up between the organs of sunflower at early and middle reproductive growth stages. The roles of transpiration and allometry were investigated.

Methods

Sunflowers were grown hydroponically in greenhouse, being exposed to low concentrations of Cd (pCd²⁺ = 11.03). At flower bud and grain filling stages, plants were exposed for three days to ¹¹¹Cd and at the same time, subjected or not to fans to increase the transpiration. The partitioning of ¹¹¹Cd between plant organs measured by high resolution ICP-MS was then modelled.

Results

Although the use of fans increased the plant water uptake and transpiration by about 20%, there were no significant effects on the partitioning of recent Cd. Most of the recent Cd was recovered in roots (60%) and only 2.8% were found in seeds (0.8% for the husk and 2.0% for the almonds). The sequestration of recent Cd in a plant organ was successfully explained by its biomass and except for leaves, by the biomass of other organs acting as competitive sinks.

Conclusions

This work proposes a modelling approach for the partitioning of the labelled Cd between plant organs in sunflower.

     

Argiotoxin in the closed AMPA receptor channel: experimental and modeling study

Binding of argiotoxin in the closed state of Ca(2+)-permeable AMPA receptor channels was studied using electrophysiological and molecular modeling approaches. Experimental study unambiguously revealed that argiotoxin is trapped in the closed AMPA receptor channels after agonist dissociation. Docking of the argiotoxin to the channel model based on recently published X-ray structure demonstrated that the drug can be effectively accommodated in the cavity of the closed channel only if the terminal moiety of the molecule penetrates in the narrow portion of the pore below the selectivity filter. Combining these results, we conclude that the selectivity filter of the AMPA receptor channels is not sterically occluded in the closed state.     

Depletion of the histone chaperone tNASP inhibits proliferation and induces apoptosis in prostate cancer PC-3 cells

Background  

NASP (Nuclear Autoantigenic Sperm Protein) is a histone chaperone that is present in all dividing cells. NASP has two splice variants: tNASP and sNASP. Only cancer, germ, transformed, and embryonic cells have a high level of expression of the tNASP splice variant. We examined the consequences of tNASP depletion for prostate cancer PC-3 cells.     

Na+ channel distribution and electrophysiological heterogeneities in guinea pig ventricular wall

We sought to explore the distribution pattern of Na(+) channels across ventricular wall, and to determine its functional correlates, in the guinea pig heart. Voltage-dependent Na(+) channel (Na(v)) protein expression levels were measured in transmural samples of ventricular tissue by Western blotting. Isolated, perfused heart preparations were used to record monophasic action potentials and volume-conducted ECG, and to measure effective refractory periods (ERPs) and pacing thresholds, in order to assess excitability, electrical restitution kinetics, and susceptibility to stimulation-evoked tachyarrhythmias at epicardial and endocardial stimulation sites. In both ventricular chambers, Na(v) protein expression was higher at endocardium than epicardium, with midmyocardial layers showing intermediate expression levels. Endocardial stimulation sites showed higher excitability, as evidenced by lower pacing thresholds during regular stimulation and downward displacement of the strength-interval curve reconstructed after extrasystolic stimulation compared with epicardium. ERP restitution assessed over a wide range of pacing rates showed greater maximal slope and faster kinetics at endocardial than epicardial stimulation sites. Flecainide, a Na(+) channel blocker, reduced the maximal ERP restitution slope, slowed restitution kinetics, and eliminated epicardial-to-endocardial difference in dynamics of electrical restitution. Greater excitability and steeper electrical restitution have been associated with greater arrhythmic susceptibility of endocardium than epicardium, as assessed by measuring ventricular fibrillation threshold, inducibility of tachyarrhythmias by rapid cardiac pacing, and the magnitude of stimulation-evoked repolarization alternans. In conclusion, higher Na(+) channel expression levels may contribute to greater excitability, steeper electrical restitution slopes and faster restitution kinetics, and greater susceptibility to stimulation-evoked tachyarrhythmias at endocardium than epicardium in the guinea pig heart.