Mutations that destabilize the a' domain of human protein-disulfide isomerase indirectly affect peptide binding

Protein-disulfide isomerase (PDI) is a catalyst of folding of disulfide-bonded proteins and also a multifunctional polypeptide that acts as the beta-subunit in the prolyl 4-hydroxylase alpha(2)beta(2)-tetramer (P4H) and the microsomal triglyceride transfer protein alphabeta-dimer. The principal peptide-binding site of PDI is located in the b' domain, but all domains contribute to the binding of misfolded proteins. Mutations in the C-terminal part of the a' domain have significant effects on the assembly of the P4H tetramer and other functions of PDI. In this study we have addressed the question of whether these mutations in the C-terminal part of the a' domain, which affect P4H assembly, also affect peptide binding to PDI. We observed a strong correlation between P4H assembly competence and peptide binding; mutants of PDI that failed to form a functional P4H tetramer were also inactive in peptide binding. However, there was also a correlation between inactivity in these assays and indicators of conformational disruption, such as protease sensitivity. Peptide binding activity could be restored in inactive, protease-sensitive mutants by selective proteolytic removal of the mutated a' domain. Hence we propose that structural changes in the a' domain indirectly affect peptide binding to the b' domain.     

Population dynamics of an expanding passerine at the distribution margin

Individuals may be maladapted to novel environments at the species’ distribution margin. We investigated population dynamics in a marginal habitat where reproduction has been proven poor. Survival, population growth rate (λ) and its components, breeding and natal dispersal were studied in great tits Parus major breeding at the northern margin of its distribution in northern Finland. We used long term capture–mark–recapture data sets. Study area size and population density were used to explain adult survival rates. The average annual estimates of adult survival rose from 0.371 to 0.388 between the periods of 1971–1984 and 1999–2009. The estimates are slightly lower than estimates of small passerines in Europe. Low local survival rate of fledglings (0.050–0.055) probably reflects intensified emigration from this low quality area. Temporal variation in λ was large (0.498–1.856). Despite of low adult survival and recruitment rates, the mean estimates of λ (1.008 and 1.033) indicate an overall stability in the population size. Indeed, our results suggest that the immigration has an important role in the population dynamics of northern great tits. Thus the population is demographically and genetically dependent on core habitats which may cause adaptive problems due to intensive gene flow. Given those limitations, options for evolution of local adaptations in northern distribution margins are discussed.     

Highly-potent,synthetic APOBEC3s restrict HIV-1 through deamination-independent mechanisms

The APOBEC3 (A3) genes encode cytidine deaminase proteins with potent antiviral and anti-retroelement activity. This locus is characterized by duplication, recombination, and deletion events that gave rise to the seven A3s found in primates. These include three single deaminase domain A3s (A3A, A3C, and A3H) and four double deaminase domain A3s (A3B, A3D, A3F, and A3G). The most potent of the A3 proteins against HIV-1 is A3G. However, it is not clear if double deaminase domain A3s have a generalized functional advantage to restrict HIV-1. In order to test whether superior restriction factors could be created by genetically linking single A3 domains into synthetic double domains, we linked A3C and A3H single domains in novel combinations. We found that A3C/A3H double domains acquired enhanced antiviral activity that is at least as potent, if not better than, A3G. Although these synthetic double domain A3s package into budding virions more efficiently than their respective single domains, this does not fully explain their gain of antiviral potency. The antiviral activity is conferred both by cytidine-deaminase dependent and independent mechanisms, with the latter correlating to an increase in RNA binding affinity. T cell lines expressing this A3C-A3H super restriction factor are able to control replicating HIV-1ΔVif infection to similar levels as A3G. Together, these data show that novel combinations of A3 domains are capable of gaining potent antiviral activity to levels similar to the most potent genome-encoded A3s, via a primarily non-catalytic mechanism.     

Combs and sexual selection in black grouse (Tetrao tetrix)

We studied supra-orbital combs in lekking black grouse (Tetrao tetrix) in relation to sexual selection at five leks in Finland1991-1998 and four leks in Sweden 1992-1995. Comb size wasestimated in two ways: by observing its natural size in thefield at different behaviors ("observed comb size"), and bymeasuring the comb size from captured birds ("measured combsize"). The size of combs is highly variable, and individualscan change it within seconds. Males express their larger combsduring display, as compared to other behaviors. Observed mean comb sizes were larger on leks with a higher number of malesand a higher number of copulations. Measured and observed combsizes and copulatory success did not significantly correlatewhen all males where analyzed, but a positive and significantrelationship between observed comb size and copulatory success was found within males that achieved copulations. Measured comblength correlated positively with the amount of testosterone.While females were present on the lek, displaying and successfulmales showed the largest observed comb size. When we comparedobserved comb size during fighting between successful and unsuccessfulmales and correlated comb size of pairs of fighting males withtheir fighting activity, no significant differences in combsize were found. The result that comb size correlated significantlywith an increase in testosterone level and that larger combsize, within successful males, predicted higher copulatorysuccess suggests that combs may be a cue for females to assessmale quality. The lack of a significant relationship betweenobserved comb size and fighting behavior suggests that combsize either has minor importance in male-male signaling onthe lek or that males may express similar-sized combs duringfighting to avoid serious fights and thus risk of comb injuries.     

Genotypic and phenotypic variation in transmission traits of a complex life cycle parasite

Characterizing genetic variation in parasite transmission traits and its contribution to parasite vigor is essential for understanding the evolution of parasite life‐history traits. We measured genetic variation in output, activity, survival, and infection success of clonal transmission stages (cercaria larvae) of a complex life cycle parasite (Diplostomum pseudospathaceum). We further tested if variation in host nutritional stage had an effect on these traits by keeping hosts on limited or ad libitum diet. The traits we measured were highly variable among parasite genotypes indicating significant genetic variation in these life‐history traits. Traits were also phenotypically variable, for example, there was significant variation in the measured traits over time within each genotype. However, host nutritional stage had no effect on the parasite traits suggesting that a short‐term reduction in host resources was not limiting the cercarial output or performance. Overall, these results suggest significant interclonal and phenotypic variation in parasite transmission traits that are not affected by host nutritional status.     

An animal model of pulmonary radiation fibrosis with biochemical, physiologic, immunologic, and morphologic observations

An animal model of pulmonary radiation fibrosis was established, using male CBA/j mice. Both lungs of each mouse in one group (DL) were irradiated with two doses of 8.5 Gy each, separated by 30 days. A control group (CG) was sham-irradiated. There was a small but significant difference (P less than 0.03) in average breathing rate between DL and CG 27 weeks after the second irradiation which increased until the 34th week followed by a plateau. The accumulated hydroxyproline content of the irradiated mouse lung was 40% greater (P less than 0.02) than that of the sham-irradiated lung at 42 weeks and thereafter. Anticollagen antibodies assayed 52 weeks after irradiation by enzyme-linked immunosorbent assay were elevated by 49% in sera from the irradiated mice compared to sera from sham-irradiated mice. Mortality during the 52-week period following the second irradiation was low (13%) for both groups. Histological comparison of irradiated and control mouse lungs fixed under uniform inflation pressure indicated no significant differences. The model has unique features including an increase in collagen deposition, no acute changes attributable to radiation, a small but statistically significant abnormality in pulmonary function, an immunologic response to collagen, and low mortality.     

Muscle strength and body composition as determinants of blood pressure in young men

The correlations of blood pressure to various indices of muscularity and fatness were studied in 183 young healthy men (mean age 19.7, SD 2.1 years). Systolic pressure showed significant positive correlations with body fat percentage, isometric strength of trunk extensors, body mass index, lean body mass, strength of leg extensors, heart rate, and the sum of four skinfolds. Diastolic pressure had significant positive correlations with body mass index, lean body mass, body fat percentage, sum of skinfolds, strength of leg extensors, strength of trunk extensors, and age. A stepwise selective multiple regression analysis for systolic pressure resulted in four significantly correlating variables: body fat percentage (p less than 0.001), heart rate (p less than 0.01), lean body mass (p less than 0.05), and strength of trunk extensors per kg body weight (p less than 0.05). For diastolic pressure the analysis resulted in two explaining variables: body mass index (p less than 0.001) and age (p less than 0.05). In a regression equation with 13 variables the strength of trunk flexors was negatively correlated with diastolic pressure. It is concluded that both fatness and muscularity are factors related to blood pressure in young men. The muscularity effect is more clearly associated with trunk and leg extensor strength.     

Differentiation in parasitism among ecotypes of whitefish segregating along depth gradients

Parasitism is a potential mechanism initiating or facilitating ecotypic differentiation and speciation in freshwater fish. While recent studies have begun to explore this question, there are no empirical studies of parasitism in evolutionary replicates of ecotype‐pairs at variable stages of speciation. Such comparative studies of parasitism along continuums of host differentiation are needed as a first step towards testing the role of parasites in ecological speciation. We explored parasitism of whitefish Coregonus lavaretus in four pre‐alpine lakes in Switzerland that hold replicate species radiations of whitefish. We sampled shallow and deep‐spawning ecotypes on their breeding grounds. We found significant and consistent differences in infection between the ecotypes so that the shallow‐spawning fish had more trematode infections, whereas the deepspawning fish had more cestodes. The magnitude of these differences correlated positively with the degree of the genetic differentiation among the ecotypes and negatively with the extent of eutrophication of the lakes. Although the overall diversity of infections was low, some parasite species with potential effects on fish showed marked differences in infection between the ecotypes, suggesting that parasitism may have a role in maintaining ecotype differentiation in this system. Our results also indicate previously unknown habitat segregation of the better differentiated ecotypes, i.e. species, along the depth gradient outside the breeding season. Moreover, oligotrophic lakes tended to have higher parasite species richness and higher abundances of infection, than mesotrophic and eutrophic lakes, suggesting that the history of eutrophication affects parasite diversity.