Vibration attraction response is a plastic trait in blind Mexican tetra (Astyanax mexicanus), variable within subpopulations inhabiting the same cave

Animals evolve their sensory systems and foraging behaviours to adapt and colonize new and challenging habitats such as the dark cave environment. Vibration attraction behaviour (VAB) gives fish the ability to locate the source of a water disturbance in the darkness. VAB evolved in the blind Mexican cave tetra, Astyanax mexicanus. VAB is triggered in cavefish by vibration stimuli peaking at 35 Hz, which is within the main spectrum of water fluctuations produced by many prey crustaceans and insects. VAB has a genetic component and is correlated to an increased number of head mechanosensory neuromasts in the eye orbital region when compared to surface fish. Previous competitive prey capture assays have supported the advantage of VAB for foraging in the dark. Despite its putative adaptive function, VAB has been described as absent in some Astyanax cave populations (Tinaja and Molino) but present in others (Pachón, Piedras, Toro and Sabinos). Here we have tested the occurrence of VAB in the field and in multiple cave populations using a vibrating device in natural pools. Our results confirmed the presence of VAB in caves such as Pachón, Toro and Sabinos but showed that VAB is also present in the Tinaja and Molino cave populations, previously reported as VAB-negative in laboratory experiments. Thus, VAB is available throughout the range of hypogean A. mexicanus. However, and most notably, within a given cave the levels of VAB were highly variable among different pools. Fish at one pool may express no VAB, while fish at another nearby pool of the same cave may actively show VAB. While a variety of environmental conditions may foster this diversity, we found that individuals inhabiting pools with a high abundance of organic matter have reduced expression of VAB. In contrast, in pools with little organic debris where fish probably depend more on hunting than on scavenging, VAB is enhanced. Our results suggest that expression of VAB is a plastic trait whose variability can depend on local conditions. Such plasticity may be required within and among caves where high environmental variability between pools results in a diverse availability of food.     

Humoral and cellular capsid-specific immune responses to adeno-associated virus type 1 in randomized healthy donors

A major impediment to the use of adeno-associated virus (AAV)-mediated gene delivery to muscle in clinical applications is the pre-existing immune responses against the vector. Pre-existing humoral response to different AAV serotypes is now well documented. In contrast, cellular responses to AAV capsid have not been analyzed in a systematic manner, despite the risk of T cell reactivation upon gene transfer. AAV1 has been widely used in humans to target muscle. In this study, we analyzed PBMCs and sera of healthy donors for the presence of AAV1 capsid-specific T cell responses and AAV1 neutralizing factors. Approximately 30% of donors presented AAV1 capsid-specific T cells, mainly effector memory CD8(+) cells. IFN-γ-producing cells were also observed among effector memory CD4(+) cells for two of these donors. Moreover, to our knowledge, this study shows for the first time on a large cohort that there was no correlation between AAV1-specific T cell and humoral responses. Indeed, most donors presenting specific Ig and neutralizing factors were negative for cellular response (and vice versa). These new data raise the question of prescreening patients not only for the humoral response, but also for the cellular response. Clearly, a better understanding of the natural immunology of AAV serotypes will allow us to improve AAV gene therapy and make it an efficient treatment for genetic disease.     

Alpha repeat proteins (αRep) as expression and crystallization helpers

We have previously described a highly diverse library of artificial repeat proteins based on thermostable HEAT-like repeats, named αRep. αReps binding specifically to proteins difficult to crystallize have been selected and in several examples, they made possible the crystallization of these proteins. To further simplify the production and crystallization experiments we have explored the production of chimeric proteins corresponding to covalent association between the targets and their specific binders strengthened by a linker. Although chimeric proteins with expression partners are classically used to enhance expression, these fusions cannot usually be used for crystallization. With specific expression partners like a cognate αRep this is no longer true, and chimeric proteins can be expressed purified and crystallized. αRep selection by phage display suppose that at least a small amount of the target protein should be produced to be used as a bait for selection and this might, in some cases, be difficult. We have therefore transferred the αRep library in a new construction adapted to selection by protein complementation assay (PCA). This new procedure allows to select specific binders by direct interaction with the target in the cytoplasm of the bacteria and consequently does not require preliminary purification of target protein. αRep binders selected by PCA or by phage display can be used to enhance expression, stability, solubility and crystallogenesis of proteins that are otherwise difficult to express, purify and/or crystallize.     

Genetic control of extracellular protease synthesis in the yeast Yarrowia lipolytica

Depending on the pH of the growth medium, the yeast Yarrowia lipolytica secretes an acidic protease or an alkaline protease, the synthesis of which is also controlled by carbon, nitrogen, and sulfur availability, as well as by the presence of extracellular proteins. Previous results have indicated that the alkaline protease response to pH was dependent on YlRim101p, YlRim8p/YlPalF, and YlRim21p/YlPalH, three components of a conserved pH signaling pathway initially described in Aspergillus nidulans. To identify other partners of this response pathway, as well as pH-independent regulators of proteases, we searched for mutants that affect the expression of either or both acidic and alkaline proteases, using a YlmTn1-transposed genomic library. Four mutations affected only alkaline protease expression and identified the homolog of Saccharomyces cerevisiae SIN3. Eighty-nine mutations affected the expression of both proteases and identified 10 genes. Five of them define a conserved Rim pathway, which acts, as in other ascomycetes, by activating alkaline genes and repressing acidic genes at alkaline pH. Our results further suggest that in Y. lipolytica this pathway is active at acidic pH and is required for the expression of the acidic AXP1 gene. The five other genes are homologous to S. cerevisiae OPT1, SSY5, VPS28, NUP85, and MED4. YlOPT1 and YlSSY5 are not involved in pH sensing but define at least a second protease regulatory pathway.     

The influence of the type of contraction on the masseter muscle EMG power spectrum

Different behaviours of the EMG power spectrum across increasing force levels have been reported for the masseter muscle. A factor that could explain these different behaviours may be the type of contraction used, as was recently shown for certain upper limb muscles⁵. The purpose of this study was to compare, between two types of isometric contractions, the behaviour of EMG power spectrum statistics (median frequency (MF) and mean power frequency (MPF)) obtained across increasing force levels. Ten women exerted, while biting in the intercuspal position, three 5 s ramp contractions that increased linearly from 0 to 100% of the maximal voluntary contraction (MVC). They also completed three step contractions (constant EMG amplitude) at each of the following levels: 20, 40, 60 and 80% MVC. EMG signals from the masseter muscle were recorded with miniature surface electrodes. The RMS, as well as the MPF and MF of the power spectrum were calculated at 20, 40, 60 and 80% MVC for each type of contraction. As expected, the RMS values showed similar increases with increasing levels of effort for both types of contractions. Different behaviours for both MPF (contraction^*force interaction, ANOVA, P<0.05) and MF (contraction^*force interaction, ANOVA, P>0.05) across increasing levels of effort were found between the two types of contraction. The use of step contractions gave rise to a decrease of both MPF and MF with increasing force, while the use of ramp contractions gave rise to an increase in both statistics up to at least 40% MVC followed by a decrease at higher force levels. These findings suggest that the type of contraction used does influence the behaviour of the spectral statistics across increasing force levels and that this could explain the differences obtained in previous studies for the masseter muscle.     

Tg (9 HSA-MYC), a homozygous lethal insertion in the mouse

Transgenic mice generated with different DNA sequences were surveyed for possible homozygous mutant phenotypes. We found an embryonic lethal mutation in the transgenic mouse strain (MT-MYC12.4) containing the human c-myc gene. Embryos homozygous for the transgene die shortly after implantation. The strain MT-MYC12.4 carries approximately 50 tandem copies of the recombinant plasmid sequence. The 3 flanking sequence has been cloned and analyzed. It contains a unique sequence that has been conserved during evolution and maps to Chromosome (Chr) 9. This mutant has been designated Tg 9 (HSA-MYC).     

The SANT2 domain of the murine tumor cell DnaJ-like protein 1 human homologue interacts with alpha1-antichymotrypsin and kinetically interferes with its serpin inhibitory activity

The murine tumor cell DnaJ-like protein 1 or MTJ1/ERdj1 is a membrane J-domain protein enriched in microsomal and nuclear fractions. We previously showed that its lumenal J-domain stimulates the ATPase activity of the molecular chaperone BiP/GRP78 (Chevalier, M., Rhee, H., Elguindi, E. C., and Blond, S. Y. (2000) J. Biol. Chem. 275, 19620-19627). MTJ1/ERdj1 also contains a large carboxyl-terminal cytosolic extension composed of two tryptophan-mediated repeats or SANT domains for which the function(s) is unknown. Here we describe the cloning of the human homologue HTJ1 and its interaction with alpha(1)-antichymotrypsin (ACT), a member of the serine proteinase inhibitor (serpin) family. The interaction was initially identified in a two-hybrid screening and further confirmed in vitro by dot blots, native electrophoresis, and fluorescence studies. The second SANT domain of HTJ1 (SANT2) was found to be sufficient for binding to ACT, both in yeast and in vitro. Single tryptophan-alanine substitutions at two strictly conserved residues significantly (Trp-497) or totally (Trp-520) abolished the interaction with ACT. SANT2 binds to human ACT with an intrinsic affinity equal to 0.5 nm. Preincubation of ACT with nearly stoichiometric concentrations of SANT2 wild-type but not SANT2: W520A results in an apparent loss of ACT inhibitory activity toward chymotrypsin. Kinetic analysis indicates that the formation of the covalent inhibitory complex ACT-chymotrypsin is significantly delayed in the presence of SANT2 with no change on the catalytic efficiency of the enzyme. This work demonstrates for the first time that the SANT2 domain of MTJ1/HTJ1/ERdj1 mediates stable and high affinity protein-protein interactions.     

Prediction of survival by neutropenia according to delivery schedule of oxaliplatin-5-Fluorouracil-leucovorin for metastatic colorectal cancer in a randomized international trial (EORTC 05963)

Circadian clocks control cellular proliferation and drug metabolism over the 24?h. However, circadian chronomodulated chemotherapy with 5-fluorouracil, leucovorin, and oxaliplatin (chronoFLO4) offered no survival benefit as compared with the non-time-stipulated FOLFOX2, in an international randomized trial involving patients with previously untreated metastatic colorectal cancer (EORTC 05963). The authors hypothesized that treatment near maximum tolerated dose could disrupt circadian clocks thus impairing the efficacy of chronoFLO4 but not of FOLFOX2. Patients with available data (N?=?556) were categorized into three subgroups according to the worst grade (G) of neutropenia experienced during treatment. Distinct multivariate models with time-dependent covariates were constructed for each treatment schedule. Neutropenia incidence (all grades) was 33% on chronoFLO4 and 61% on FOLFOX2 (p?相似文献   

Brief inactivation of c-Myc is not sufficient for sustained regression of c-Myc-induced tumours of pancreatic islets and skin epidermis

Background  

Tumour regression observed in many conditional mouse models following oncogene inactivation provides the impetus to develop, and a platform to preclinically evaluate, novel therapeutics to inactivate specific oncogenes. Inactivating single oncogenes, such as c-Myc, can reverse even advanced tumours. Intriguingly, transient c-Myc inactivation proved sufficient for sustained osteosarcoma regression; the resulting osteocyte differentiation potentially explaining loss of c-Myc's oncogenic properties. But would this apply to other tumours?