New Roles for Cyclin E in Megakaryocytic Polyploidization

Megakaryocytes are platelet precursor cells that undergo endomitosis. During this process, repeated rounds of DNA synthesis are characterized by lack of late anaphase and cytokinesis. Physiologically, the majority of the polyploid megakaryocytes in the bone marrow are cell cycle arrested. As previously reported, cyclin E is essential for megakaryocyte polyploidy; however, it has remained unclear whether up-regulated cyclin E is an inducer of polyploidy in vivo. We found that cyclin E is up-regulated upon stimulation of primary megakaryocytes by thrombopoietin. Transgenic mice in which elevated cyclin E expression is targeted to megakaryocytes display an increased ploidy profile. Examination of S phase markers, specifically proliferating cell nuclear antigen, cyclin A, and 5-bromo-2-deoxyuridine reveals that cyclin E promotes progression to S phase and cell cycling. Interestingly, analysis of Cdc6 and Mcm2 indicates that cyclin E mediates its effect by promoting the expression of components of the pre-replication complex. Furthermore, we show that up-regulated cyclin E results in the up-regulation of cyclin B1 levels, suggesting an additional mechanism of cyclin E-mediated ploidy increase. These findings define a key role for cyclin E in promoting megakaryocyte entry into S phase and hence, increase in the number of cell cycling cells and in augmenting polyploidization.     

Secretion of a lysophospholipase D activity by adipocytes: involvement in lysophosphatidic acid synthesis

The aim of the present work was to depict the metabolic pathways involved in extracellular production of lysophosphatidic acid (LPA) by adipocytes. LPA was followed by quantifying the accumulation of LPA in the incubation medium (conditioned medium, CM) of 3T3F442A adipocytes or human adipose tissue explants using a radioenzymatic assay. Surprisingly, after separation from the cells, the amount of LPA present in CM could be significantly increased by further incubation at 37 degrees C. This suggested the presence of a LPA-synthesizing activity (LPA-SA) in CM. LPA-SA appeared as a soluble activity which was inhibited by divalent ion chelators EDTA and phenanthrolin. The effect of EDTA was preferentially reverted by CoCl2, as described for a lysophospholipase D (lyso-PLD) activity previously identified in rat plasma. LPA concentration could also be increased by treatment with a bacterial PLD, demonstrating the presence of PLD-sensitive LPA precursors (mainly lysophosphatidylcholine) in adipocyte CM. LPA-SA could be increased by the addition of exogenous lysophosphatidylcholine, lysophosphatidylglycerol, or lyso-platelet activating factor, demonstrating that LPA-SA resulted from the action of a lyso-PLD. LPA-SA was not inhibited, but rather activated, by primary alcohol (ethanol and 1-butanol), suggesting that adipocyte lyso-PLD was not a classical PLD. Finally, LPA-SA was found to be weaker in CM of undifferentiated adipocyte (preadipocytes) compared with CM of differentiated adipocytes. In conclusion, our results reveal the existence of a secreted lyso-PLD activity regulated during adipocyte-differentiation and involved in extra cellular production of synthesis of LPA by adipocytes.     

Strain distribution during anchorage failure of Pinus pinaster Ait. at different ages and tree growth response to wind-induced root movement

Winching tests were carried out on 5- 13- and 17-year-old tap rooted Maritime pine (Pinus pinaster Ait.) in order to determine how the mode of anchorage failure changes throughout the life of a tree. As trees were pulled sideways, strain along the lateral roots was recorded using strain gauges attached to a strain indicator. Measurements of strain in the root system, taken during winching, provide information about root movement when loaded by wind. The mode of mechanical failure appeared to depend on tree age. The youngest trees bent over completely during winching, but did not break due to the plasticity of their trunks. The 13-year-old trees either broke at the base of the tree (due to the presence of grafting scar tissue) or at the base of the tap-root. The oldest trees broke at the base of the tap-root and sounds of roots breaking were also heard. Strain was twice as great in the trunk compared to the roots in the 5- and 13-year-old trees and was three times greater in the compression roots of 17-year–old trees compared to that in the trunk. In one 17-year-old tree, strain was found to increase at a distance of 35 cm in tension roots before decreasing again. Although the mode of failure changed with tree size, anchorage strength increased proportionally with the third power of trunk diameter, therefore another reason why failure differs with tree age must exist. In order to determine if different types of wood were being laid down in the lateral roots in response to wind loading, maturation strains, indicating the existence of mechanical stress in developing wood cells, were measured at different points along the roots. A high correlation was found between maturation strain and strain measured during winching, in roots that lay in the wind direction only. Therefore, trees appear to be able to respond to external loading stress, even at a local level within a root. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genito-sexual dysfunction in patients with a medullary lesion

Multiple dramatic consequences follow medullary lesions. Not only are voluntary motor control and sensitivity of the body segment below the lesion lost, but it also becomes impossible to control erection and ejaculation as well as urinary and faecal continency. The first investigations into genito-sexual function in paraplegics have brought about the idea, commonly admitted in the medical world, that this kind of patient is impotent and sterile. Fortunately this idea is disappearing gradually and many data have demonstrated that appropriate treatment is required and some therapies efficient. This is particularly important in the case of the population concerned, namely young men in 70% of the cases, since the usual age bracket at trauma is between 25 and 35 years old. At this time of life, sexual activity is often at its peak, so that the fertility potential becomes erased.     

Cyprus versus UK: Cultural Differences of Attitudes toward Animals Based on Personality and Sensational Interests

The aim of the present study was to see if positive attitudes toward animals can be predicted by the personality traits of agreeableness and conscientiousness, and whether higher levels of militaristic interests may lead to less positive attitudes. Militarism was expected to be predicted by lower agreeableness and conscientiousness, higher extraversion, and lower age. Known relationships between gender, age, and personality were also expected. These relationships were examined cross-culturally through a comparison between Cyprus and the UK, using measures translated for use in a Greek Cypriot sample and a new measure specifically designed for use in both UK and Cyprus samples. Cyprus, while similar to the UK in terms of its standard of living, retains a more traditional, rural lifestyle most often associated with collectivist cultures. While this study does not examine individualism and collectivism, findings may inform on any possible differences between such societies and offer a basis for more in-depth research. An online questionnaire was completed by 618 people and a path analysis was used to analyze the data, pooling the data for the analysis to determine possible cross-cultural causes for the observed differences in attitudes, personality traits, and interests. Findings indicated that individuals scoring high on agreeableness, scoring high on conscientiousness, Cypriot residents, females, and individuals expressing fewer militaristic interests expressed more positive attitudes toward animals. Additional relationships between personality, militaristic interests, and demographics were also established. The findings lend support to existing theory regarding the variables of interest and highlight significant new findings for the field. Cypriot residents reporting more positive attitudes toward animals may be a result of their collectivist culture, which appears to extend to human–animal relationships. New findings are discussed in light of suggestions for future research in the collectivist nature of Cypriot culture and its potential effects on militaristic interests and general animal welfare.     

Larval Starvation to Satiation: Influence of Nutrient Regime on the Success of Acanthaster planci

High density populations of the crown-of-thorns seastar, Acanthaster planci, are a major contributor to the decline of coral reefs, however the causes behind periodic outbreaks of this species are not understood. The enhanced nutrients hypothesis posits that pulses of enhanced larval food in eutrophic waters facilitate metamorphic success with a flow-on effect for population growth. The larval resilience hypothesis suggests that A. planci larvae naturally thrive in tropical oligotrophic waters. Both hypotheses remain to be tested empirically. We raised A. planci larvae in a range of food regimes from starvation (no food) to satiation (excess food). Algal cell concentration and chlorophyll levels were used to reflect phytoplankton conditions in nature for oligotrophic waters (0-100 cells ml^-1; 0-0.01 μg chl a L^-1), natural background levels of nutrients on the Great Barrier Reef (GBR) (1,000-10,000 cells ml^-1; 0.1-1.0 μg chl a L^-1), and enhanced eutrophic conditions following runoff events (100,000 cells ml^-1; 10 μg chl a L^-1). We determine how these food levels affected larval growth and survival, and the metamorphic link between larval experience and juvenile quality (size) in experiments where food ration per larvae was carefully controlled. Phytoplankton levels of 1 μg chl a L^-1, close to background levels for some reefs on the GBR and following flood events, were optimal for larval success. Development was less successful above and below this food treatment. Enhanced larval performance at 1 μg chl a L^-1 provides empirical support for the enhanced nutrients hypothesis, but up to a limit, and emphasizes the need for appropriate mitigation strategies to reduce eutrophication and the consequent risk of A. planci outbreaks.     

Chronic Electrical Stimulation with a Suprachoroidal Retinal Prosthesis: A Preclinical Safety and Efficacy Study

Purpose

To assess the safety and efficacy of chronic electrical stimulation of the retina with a suprachoroidal visual prosthesis.

Methods

Seven normally-sighted feline subjects were implanted for 96–143 days with a suprachoroidal electrode array and six were chronically stimulated for 70–105 days at levels that activated the visual cortex. Charge balanced, biphasic, current pulses were delivered to platinum electrodes in a monopolar stimulation mode. Retinal integrity/function and the mechanical stability of the implant were assessed monthly using electroretinography (ERG), optical coherence tomography (OCT) and fundus photography. Electrode impedances were measured weekly and electrically-evoked visual cortex potentials (eEVCPs) were measured monthly to verify that chronic stimuli were suprathreshold. At the end of the chronic stimulation period, thresholds were confirmed with multi-unit recordings from the visual cortex. Randomized, blinded histological assessments were performed by two pathologists to compare the stimulated and non-stimulated retina and adjacent tissue.

Results

All subjects tolerated the surgical and stimulation procedure with no evidence of discomfort or unexpected adverse outcomes. After an initial post-operative settling period, electrode arrays were mechanically stable. Mean electrode impedances were stable between 11–15 kΩ during the implantation period. Visually-evoked ERGs & OCT were normal, and mean eEVCP thresholds did not substantially differ over time. In 81 of 84 electrode-adjacent tissue samples examined, there were no discernible histopathological differences between stimulated and unstimulated tissue. In the remaining three tissue samples there were minor focal fibroblastic and acute inflammatory responses.

Conclusions

Chronic suprathreshold electrical stimulation of the retina using a suprachoroidal electrode array evoked a minimal tissue response and no adverse clinical or histological findings. Moreover, thresholds and electrode impedance remained stable for stimulation durations of up to 15 weeks. This study has demonstrated the safety and efficacy of suprachoroidal stimulation with charge balanced stimulus currents.