A rapid fluorometric assay for the proteolytic activity of SKI-1/S1P based on the surface glycoprotein of the hemorrhagic fever Lassa virus

The subtilase subtilisin kexin isozyme-1 (SKI-1)/site 1 protease (S1P), has been implicated in the processing of Lassa virus glycoprotein C (GP-C) precursor into GP1 and GP2 that are responsible for viral fusion with the host cell membrane. Here, we studied in vitro the kinetics of this cleavage by hSKI-1 using an intramolecularly quenched fluorogenic (IQF) peptide, Q-GPC(251-263) [Abz-(251)Asp-Ile-Tyr-Ile-Ser-Arg-Arg-Leu-Leu/Gly-Thr-Phe-Thr(263)-3-NitroTyr-Ala-CONH(2)], containing the identified site. The measured V(max (app))/K(m (app)) was compared to those for other IQF SKI-substrates. Q-GPC(251-263) is cleaved 10-fold more efficiently than the previously known best SKI-substrate, Q-hproSKI(134-142). This study confirmed the role of SKI-1 in GP-C processing and provides a novel, rapid and efficient enzymatic assay of SKI-1.     

Respiratory chain defects: what do we know for sure about their consequences in vivo?

The function and the structure of mitochondria have been the subject of intensive research since the discovery of these organelles. Yet, the investigation of patients with mitochondrial disease reveals that we do not understand a large part of the underlying pathogenic processes. This has disastrous consequences in terms of the therapy possibly proposed to the patients and their family. An attempt is made in this short review to question our present ideas on the potential consequences of mitochondrial dysfunctions and to enlighten new observations which might be valuable in the understanding of the physiopathology of these diseases.     

Mitochondria and reproduction

Mitochondria play a primary role in cellular energetic metabolism. They possess their own DNA, which is exclusively maternally transmitted. The relatively recent idea that mitochondria may be directly involved in human reproduction is arousing increasing interest in the scientific and medical community. It has been shown that the functional status of mitochondria contributes to the quality of oocytes and spermatozoa, and plays a part in the process of fertilisation and embryo development. Moreover, new techniques, such as ooplasm transfer, compromise the uniquely maternal inheritance of mitochondrial DNA, raising important ethical questions. This review discusses recent information about mitochondria in the field of human fertility and reproduction.     

Multiple causes of sexual segregation in European red deer: enlightenments from varying breeding phenology at high and low latitude

Sexual segregation outside the mating season occurs in most species of sexually dimorphic ungulates and has been extensively described in the literature, but the mechanisms causing segregation are still debated. The detailed pattern of sexual segregation throughout the year has rarely been presented for mammals, and no study, to our knowledge, has used latitudinal-related variation in breeding phenology to shed light on the underlying mechanisms. Recent methodological developments have made it possible to quantify separate components of segregation (social, habitat) and activity synchrony in animal groups, but these major improvements have so far been little used. We observed European red deer year round at two widely different latitudes (France and Norway) and tested three different mechanistic hypotheses of segregation related to: (i) predation risk; (ii) body-size-related forage selection; and (iii) activity budget. Habitat segregation peaked during calving in both populations and dropped rapidly after calving. Females with calves were more segregated from males than were females without calves, pointing to a key role of antipredator behaviour even though large predators are absent in France and extremely rare in Norway. However, at both sites individuals also grouped with their own sex within habitat types (i.e. social segregation), and individuals in mixed-sex groups were less synchronized in activity type than individuals in either unisex male or unisex female groups, suggesting that differences in activity budgets are involved. Social segregation peaked during calving and was lowest during the rut (indicating aggregation) in both populations; these activities occurred one month later in the Northern populations, corresponding well with known differences in breeding phenology. We conclude that latitude-dependent breeding phenology shapes the seasonal pattern of sexual segregation and that sexual segregation in ungulates has multiple causes.     

Ascorbic acid treatment corrects the phenotype of a mouse model of Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is the most common hereditary peripheral neuropathy, affecting 1 in 2,500 people. The only treatment currently available is rehabilitation or corrective surgery. The most frequent form of the disease, CMT-1A, involves abnormal myelination of the peripheral nerves. Here we used a mouse model of CMT-1A to test the ability of ascorbic acid, a known promoter of myelination, to correct the CMT-1A phenotype. Ascorbic acid treatment resulted in substantial amelioration of the CMT-1A phenotype, and reduced the expression of PMP22 to a level below what is necessary to induce the disease phenotype. As ascorbic acid has already been approved by the FDA for other clinical indications, it offers an immediate therapeutic possibility for patients with the disease.     

Cryptococcal Cell Morphology Affects Host Cell Interactions and Pathogenicity

Cryptococcus neoformans is a common life-threatening human fungal pathogen. The size of cryptococcal cells is typically 5 to 10 µm. Cell enlargement was observed in vivo, producing cells up to 100 µm. These morphological changes in cell size affected pathogenicity via reducing phagocytosis by host mononuclear cells, increasing resistance to oxidative and nitrosative stress, and correlated with reduced penetration of the central nervous system. Cell enlargement was stimulated by coinfection with strains of opposite mating type, and ste3 a Δ pheromone receptor mutant strains had reduced cell enlargement. Finally, analysis of DNA content in this novel cell type revealed that these enlarged cells were polyploid, uninucleate, and produced daughter cells in vivo. These results describe a novel mechanism by which C. neoformans evades host phagocytosis to allow survival of a subset of the population at early stages of infection. Thus, morphological changes play unique and specialized roles during infection.     

Testing five hypotheses of sexual segregation in an arctic ungulate

1. Sexual segregation occurs in most species of sexually dimorphic ungulates. At least five not mutually exclusive hypotheses have been formulated to explain patterns of social, habitat and spatial segregation; the indirect competition hypothesis (H1), the nutritional needs hypothesis (H2), the activity budget hypothesis (H3), the weather sensitivity hypothesis (H4), and the predation risk hypothesis (H5). 2. Each hypothesis has a unique set of predictions with respect to the occurrence of segregation, and how seasonality, density dependence and reproductive status affect sexual segregation. 3. We tested this set of predictions in order to separate the hypotheses H1-H5 for patterns of sexual segregation of the Svalbard reindeer based on 9 years data on seasonal estimates of spatial, habitat and social (i.e. grouping with their own sex) segregation in combination with resource selection functions. 4. Our results do not support that one single mechanism causes segregation. The activity budget hypothesis, the nutritional needs hypothesis and the weather sensitivity hypothesis were all partially supported, while the predation risk hypothesis was discarded for Svalbard reindeer because predators have been absent for at least 5000 years. Several mechanisms are thus interacting to explain the full-year pattern of sexual segregation and the combination of mechanisms varies among species and populations.     

Activity pattern of arctic reindeer in a predator-free environment: no need to keep a daily rhythm

Arctic Cervids face considerable challenges in sustaining life in a harsh and highly seasonal environment, and when to forage is a key component of the survival strategy. We predict that a cervid maximizes net intake of energy to change the duration of feeding-ruminating cycles depending on season, and pays no attention to light or other activity-entraining cues. Still, in periods of bad weather it may pay energetically to reduce exposure and heat loss. We investigated environmental impact on the seasonal and daily activity pattern of a food-limited, predator-free arctic deer, the Svalbard reindeer. We found that the reindeer indeed had season-dependent feeding-rumination intervals, with no distinct peaks in activity at sunrise and sunset, as would be expected if animals maximize energy intake rates in predator-free environments. However, they temporarily reduced activity when exposed to low temperature and increased precipitation during winter, possibly to conserve energy. We provide insight into the behavioural strategy of Svalbard reindeer which enables them to cope with such an extreme environment.