Homodimerization as a molecular switch between low and high efficiency PrPC cell surface delivery and neuroprotective activity

PrP^C is associated with a variety of functions, and its ability to interact with a multitude of partners, including itself, may largely explain PrP multifunctionality and the lack of consensus on the genuine physiological function of the protein in vivo. In contrast, there is a consensus in the literature that alterations in PrP^C trafficking and intracellular retention result in neuronal degeneration. In addition, a proteolytic modification in the late secretory pathway termed the α-cleavage induces the secretion of PrPN1, a PrP^C-derived metabolite with fascinating neuroprotective activity against toxic oligomeric Aβ molecules implicated in Alzheimer disease. Thus, studies focusing on understanding the regulation of PrP^C trafficking to the cell surface and the modulation of α-cleavage are essential. The objective of this commentary is to highlight recent evidences that PrP^C homodimerization stimulates trafficking of the protein to the cell surface and results in high levels of PrPN1 secretion. We also discuss a hypothetical model for these results and comment on future challenges and opportunities.     

Evolution of pseudogenes in the immunoglobulin V H-gene family of the mouse

A quantitative analysis of the complexity of the J558 V _H -gene family in the mouse immunoglobulin heavy chain (Igh) gene locus has been performed. Considerable variations in the degree of complexity are observed in various Igh haplotypes derived from laboratory mice and wild mice. The BALB/c strain shows the highest degree of complexity of the J558 V _H -gene family when all mice are compared. Multiple gene duplications seem to have occurred in the BALB/c-derived J558 V_H-gene family less than 1–2 million years ago. This dating is supported by the divergence in coding and flanking regions of three strongly homologous V _H -region genes. Two of these genes were generated by the duplication of a pseudogene about 1.5 × 10⁵ years ago. A recent expansion of the J558 V _H -gene family and therefore little time for evolutionary drift may explain why most of the pseudogenes in this family exhibit a largely intact structure. We also describe two V _H -region genes which represent older pseudogenes in states of progressive disintegration.     

Heteroplasmy in mice with deletion of a large coding region of mitochondrial DNA

Polymorphism of animal mitochondrial DNA (mtDNA) has been shown to involve point mutations and limited length variations affecting essentially noncoding regions. In two wild mice of the European subspecies Mus mus musculus we found a mitochondrial mutant with a very large deletion in a coding region. The deletion is 5 kbp long (31% of the mitochondrial chromosome) and encompasses six tRNA genes and seven protein genes. The two mice were heteroplasmic: they contained a mixture of normal mtDNA and the deletion mutant. Although the latter is functionally defective, it represents 78%-79% of the mtDNA molecules in our preparations from each animal.      

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

A theoretical analysis of radiation interception in a two-species plant canopy.

Classical radiation interception laws for monospecific canopies cannot be used directly for bispecific canopies. They are always based on the gap frequency concept (i.e., the probability of no interception), which does not provide any information about the sharing of intercepted radiation between species. A theoretical analysis is reported that relates the radiation interception probabilities to the geometrical structure of the crop (i.e., the leaf area density and the leaf angle distribution of each component) and the foliage dispersion. The leaf dispersion globally describes the spatial relations between the leaf elements; it may be regular if the leaves avoid mutual shading, random, or clumped if they tend to overlap. For such two-species canopies, the leaf dispersions within each component (WSLD: within-species leaf dispersion) and between two species (BSLD: between-species leaf dispersion) are distinguished. Using bivariate multinomial distributions, general expressions for the gap frequency and the interception probabilities of a homogeneous vegetation layer were set as exponential functions of the foliage thickness, taking into account a number of dispersion parameters as small as possible. First, one WSLD for each species describes the rate of foliage overlap between the leaves of this species; it is quite similar to the leaf dispersion of single-species canopies. Second, the rate of foliage overlap between species is characterized by one BSLD. As in monospecific canopies, this parameter is positive, zero, or negative, respectively, for regular, random, or clumped BSLD. Third, another BSLD parameter has to be used if the foliage overlap between species is more than random (i.e., in the case of clumped BSLD); the latter shows the direction of overlap between species and may be taken as the probability of finding a leaf element of the first species in the case of marked overlapping. Suggestions for estimating the leaf dispersion parameters and possible uses of such relations are also discussed.     

Effects of direct transfer from freshwater to seawater on respiratory and circulatory variables and acid-base status in rainbow trout

Summary The effects of increased ambient salinity (35 mg · ml^-1) were studied at 1, 6, and 24 h after direct transfer of rainbow trout from freshwater to seawater. Two series of experiments were carried out successively. The first series was designed to simultaneously study all the respiratory (except Hb affinity for O₂), circulatory, and acid-base variables in each fish. In this series, fish were fitted with catheters chronically inserted into the cardiac bulbus, the dorsal aorta, and the opercular and buccal cavities. In the second series, designed to study haemoglobin O₂ affinity, fish were fitted with only a dorsal aorta catheter. The ventilatory flow ( ) was markedly increased just after transfer (by 55% at 1 h), then more moderately (by 20% at 6 h and 32% at 24 h). The initial hyperventilation peak was associated with frequent couphing motions. These ventilatory changes resulted essentially from increase in ventilatory amplitude. Initially, standard oxygen consumption (MM}O₂) decreased slightly, the moderately increased (by 12% at 24 h), so that the oxygen convection requirement ( ) increased substantially. In spite of an increased ventilation, the partial pressure of oxygen in arterial blood (P _aO₂) decreased slightly at 1 h, prior to returning to control levels, while partial pressure of carbon dioxide in arterial blood (P _aCO₂) was not significantly decreased. Gill oxygen transfer factor decreased substantially at 1 h (by 35%) then more moderately (by 7% at 1 h and 12% at 24 h). These results suggest a decrease in gas diffusing capacity of the gills. As P _aCO₂ remained approximatively unchanged, the gradual decrease in arterial pH (pH_a) from 7.94 to 7.67 at 24 h must therefore be regarded as a metabolic acidosis. The strong ion difference decreased markedly because the concentration of plasma chloride increased more than that of sodium. Arterial O₂ content (C _aO₂) gradually decreased (by 38% at 24 h) simultaneously with the decrease in pH_a, while the ratio P _aO₂/C _aO₂ increased. In parallel, seawater exposure induced a marked decrease in affinity of haemoglobin for O₂, so that at 24 h, P₅₀ was increased by 26% above the value obtained in freshwater-adapted trout. The increase in could be ascribed initially (at 1 h) to the decrease of P _aO₂ and later to a stimulation of respiratory neurons resulting from the lowered medullary interstitial pH. The decrease in C _aO₂ could be interpreted mainly as a consequence of a decreased affinity of haemoglobin for O₂, likely to be due to the blood acidosis and a predictable increase in chloride concentration within erythrocytes. Cardiac output ( ) slightly decreased at 1 h, then progressively increased by 30% at 24 h. Branchial vascular resistance increased at 1 h by 28%, then decreased by 18% of the control value at 24 h. Systemic vascular resistance decreased markedly by 40% at 24 h. As heart rate (HR) remained significantly unchanged, the cardiac stroke volume initially decreased then increased in relation to the changes in . The increase of , allowing compensation for the effect of decreased C _aO₂ in tissue O₂ supply, was interpreted as a passive consequence of the decrease in total vascular resistance occurring during seawater exposure.Abbreviations a.u. arbitrary units - C _aO₂ arterial oxygen content - pH₅₀ arterial pH at P₅₀ - C _vO₂ venous oxygen content - Hb haemoglobin - HR heart rate - Hct hematocrit - n_Hill Hill coefficient - O₂ standard oxygen consumption - P _aCO₂ arterial partial pressure of carbon dioxide - P _aO₂ arterial partial pressure of oxygen - P _vO₂ oxygen partial pressure in mixed venous blood - P₅₀ oxygen tension at half saturation of haemoglobin - P _VA, P _DA blood pressure in ventral and dorsal aorta - pH_a arterial pH - PIO₂, PEO₂ oxygen partial pressure of inspired and expired water - PO₂ oxygen partial pressure - cardiac output - SEM standard error of mean - S.I.D. strong ion difference - SV cardiac stroke volume - TO₂ gill oxygen transfer factor - U oxygen extraction coefficient - VA ventilatory amplitude - VF ventilatory frequency - VR_G, VR_S branchial and systemic vascular resistances - ventilatory flow - ventilatory oxygen convection requirement     

Quantitative immunolocalization of four immunodominant antigens of Toxoplasma gondii

Ultrastructural localization of four immunodominant antigens of Toxoplasma gondii was investigated quantitatively on thin sections and replicas by an immunogold technique using four monoclonal antibodies (Mab). On immunoblot Mab IV47, GII9, II38 and IE10 identified proteins of 28, 30, 45 and 66-70 kDa, respectively. Use of digital image analyzer and a semi-automatic procedure developed by us, the patterns of label distribution were compared in three cell structures: cell surface, submembrane area and rhoptries. On the whole cell surface, protein P28 and P30 were 2.5 and 4 times more abundant than P66-70 respectively. The protein P28 was essentially concentrated in the submembrane area with a labeling of 195.4 +/- 46.7 gold particles/microns 2 that follows a decreasing gradient from this area to the cell centre. In the rhoptries, all four antigens were detected, P45 and P66-70 being major with a labeling of 97.1 +/- 31.1 gold particles/microns 2 and 155.1 +/- 39.3 gold particles/microns 2 respectively. The results support the hypothesis that rhoptries are the essential site for antigen storage.     

H-2 Polymorphisms Are More Uniformly Distributed than Allozyme Polymorphisms in Natural Populations of House Mice

Patterns of H-2 and allozyme polymorphism in natural populations of house mice from Europe, North Africa and South America were analyzed. The purpose of the analysis was to determine whether H-2 and allozyme polymorphisms were similarly distributed both geographically and temporally in wild mice. Two subspecies of house mice, Mus musculus domesticus and M. m. musculus were sampled and the polymorphisms of two H-2 class I genes, H-2K and H-2D, and 34 allozyme-encoding genes were surveyed. The three kinds of analyses that were conducted included a hierarchical gene diversity analysis, an analysis of the effects of barriers to gene flow, and an analysis of similarity networks. Each of the comparisons demonstrated that H-2 polymorphisms were more uniformly distributed than allozyme polymorphisms and provided additional evidence that H-2 and allozyme polymorphisms are subject to different evolutionary pressures. The analysis of similarity networks also demonstrated that H-2 genes provide little information about the phylogeny of wild mice.     

Serological survey of T-lymphocyte differentiation antigens in wild mice

Allelic distributions of Thy-1, Ly-l, and Ly-2 antigens in wild mice are characteristic of each Mus musculus subspecies. Eastern mice (M.m.molossinus, M.mmusculus, M.m.castaneus, M.m.bactrianus) express the Thy-1.1 antigen, whereas Western mice (M.m. domesticus, M.m.brevirostris) express the Thy-1.2. All mice from wild populations examined in this survey express the Ly-1.2. The Ly-2.1 is distributed in Eastern mice and some Western mice, and the Ly-2.2 is found in the remaining Western mice. Allelic distributions of these antigens were also examined in two other species, Mus spretus and Mus spicilegus. Allelic constitutions of Thy-1 and Ly-1 in these species are similar to those of Eastern mice. Some M.spicilegus, however, express the Ly-1.1 antigen. This antigenic type is not found in M.musculus. Some Eastern mice related to M.m.castaneus react weakly to Ly-1.2-specific and Ly-2.1-specific monoclonal antibodies in both the complement-mediated cytotoxicity test and the absorption test. These results suggest that M.m.castaneus has unique alleles in the Ly-1 and Ly-2 loci.     

Characterization of newly isolated monoclonal antibodies against MHC of a Japanese wild mouse

We have already developed nine B10.MOL congenic strains carrying H-2 haplotypes derived from Japanese wild mice, Mus musculus molossinus, with the C57BL/10 genetic background. To obtain monoclonal antibodies against the H-2 antigen of the Japanese wild mouse, we carried out cell fusion using spleen cells from the animal immunized with one of the B10.MOL strains, B10.MOL-SGR (H-2 ^wm7). As a result, 19 hybridomas producing monoclonal antibodies were produced. Analysis with the intro-H-2 recombinants derived from B10.MOL-SGR indicated that 8 of them reacted with the class I and II with the class II molecule. The class I antibodies were tested for their cross -reactivities on wild mice and on the panels of standard inbred and B10.MOL strains. Most of the antibodies reacted with both the Japanese wild mice and the other subspecies, including standard inbred, while two antibodies highly specific for the donor H-2K region reacted with only three wild-derived mice, two M. m. molossinus from Anj o and Shizuoka, Japan, and one M. m. domesticus from Pigeon, Canada. In addition, all of the other four antibodies reactive with the K antigen of B10.MOL-SGR also reacted with the same three wild mice. The wild mice belonging to different subspecies might share very similar H-2K antigenic determinants in spite of their genetic and geographical remoteness.