Evolution of defences against cuckoo (<Emphasis Type="Italic">Cuculus canorus</Emphasis>) parasitism in bramblings (<Emphasis Type="Italic">Fringilla montifringilla</Emphasis>): a comparison of four populations in Fennoscandia

The brood parasitic common cuckoo Cuculus canorus has a history of coevolution that involves numerous passerine hosts, but today only a subset is known to be regularly parasitised in any area. In some hosts, there is significant variation in the occurrence of parasitism between populations, but still individuals in non-parasitised populations show strong antiparasite defences. In the present study we compared the strength of egg rejection of four distant Fennoscandian brambling Fringilla montifringilla populations experiencing different levels of cuckoo parasitism (0–6%). Egg rejection ability was in general very well developed and we did not find any population differences in the relationship between egg rejection probability and similarity between host and experimental parasitic eggs. Furthermore, bramblings very rarely made errors in rejection, indicating that selection against rejection behaviour is likely to be very weak. The brambling-cuckoo system therefore differs from other well studied systems which are characterised by pronounced spatial and temporal variation in the host’s level of defence. This result is unlikely to reflect independent replication of the same evolutionary trajectory because the weak breeding site tenacity of bramblings should result in an extreme amount of gene flow within the distribution area and thus strongly impede localised responses to selection. Instead, lack of geographic variation has more likely arisen because bramblings respond to selection as one evolutionary unit, and because the average parasitism pressures have been high enough in the past to cause regional fixation of rejection alleles and evolution of clutch characteristics that facilitate cost free egg recognition.     

Hantavirus infections in fluctuating host populations: the role of maternal antibodies

Infected females may transfer maternal antibodies (MatAbs) to their offspring, which may then be transiently protected against infections the mother has encountered. However, the role of maternal protection in infectious disease dynamics in wildlife has largely been neglected. Here, we investigate the effects of Puumala hantavirus (PUUV)-specific MatAbs on PUUV dynamics, using 7 years'' data from a cyclic bank vole population in Finland. For the first time to our knowledge, we partition seropositivity data from a natural population into separate dynamic patterns for MatAbs and infection. The likelihood of young of the year carrying PUUV-specific MatAbs during the breeding season correlated positively with infection prevalence in the overwintered parent population in the preceding spring. The probability of PUUV infection varied between seasons (highest in spring, lowest in late summer) and depended on population structure, but was also, in late autumn, notably, negatively related to summer MatAb prevalence, as well as to infection prevalence earlier in the breeding season. Hence, our results suggest that high infection prevalence in the early breeding season leads to a high proportion of transiently immune young individuals, which causes delays in transmission. This suggests, in turn, that MatAb protection has the potential to affect infection dynamics in natural populations.     

Ligand-binding Domain Determines Endoplasmic Reticulum Exit of AMPA Receptors

AMPA receptors (AMPARs) are tetrameric ion channels that mediate rapid glutamate signaling in neurons and many non-neuronal cell types. Endoplasmic reticulum (ER) quality control mechanisms permit only correctly folded functional receptors to be delivered to the cell surface. We analyzed the biosynthetic maturation and transport of all 12 GluA1–4 subunit splice variants as homomeric receptors and observed robust isoform-dependent differences in ER exit competence and surface expression. In contrast to inefficient ER exit of both GluA3 splice forms and the flop variants of GluA1 and GluA4, prominent plasma membrane expression was observed for the other AMPAR isoforms. Surprisingly, deletion of the entire N-terminal domain did not alter the transport phenotype, nor did the different cytosolic C-terminal tail splice variants. Detailed analysis of mutant receptors led to the identification of distinct residues in the ligand-binding domain as primary determinants for isoform-specific maturation. Considered together with the essential role of bound agonist, our findings reveal the ligand-binding domain as the critical quality control target in AMPAR biogenesis.     

Liposome-based vascular endothelial growth factor-165 transfection with skeletal myoblast for treatment of ischaemic limb disease

The study aims to use cholesterol (Chol) + DOTAP liposome (CD liposome) based human vascular endothelial growth factor-165 (VEGF(165)) gene transfer into skeletal myoblasts (SkMs) for treatment of acute hind limb ischaemia in a rabbit model. The feasibility and efficacy of CD liposome mediated gene transfer with rabbit SkMs were characterized using plasmid carrying enhanced green fluorescent protein (pEGFP) and assessed by flow cytometry. After optimization, SkMs were transfected with CD lipoplexes carrying plasmid-VEGF(165) (CD-pVEGF(165)) and transplanted into rabbit ischaemic limb. Animals were randomized to receive intramuscular injection of Medium199 (M199; group 1), non-transfected SkM (group 2) or CD-pVEGF(165) transfected SkM (group 3). Flow cytometry revealed that up to 16% rabbit SkMs were successfully transfected with pEGFP. Based on the optimized transfection condition, transfected rabbit SkM expressed VEGF(165) up to day 18 with peak at day 2. SkMs were observed in all cell-transplanted groups, as visualized with 6-diamidino-2-phenylindole and bromodeoxyuridine. Angiographic blood vessel score revealed increased collateral vessel development in group 3 (39.7 +/- 2.0) compared with group 2 (21.6 +/- 1.1%, P < 0.001) and group 1 (16.9 +/- 1.1%, P < 0.001). Immunostaining for CD31 showed significantly increased capillary density in group 3 (14.88 +/- 0.9) compared with group 2 (8.5 +/- 0.49, P < 0.001) and group 1 (5.69 +/- 0.3, P < 0.001). Improved blood flow (ml/min./g) was achieved in animal group 3 (0.173 +/- 0.04) as compared with animal group 2 (0.122 +/- 0.016; P= 0.047) and group 1 (0.062 +/- 0.012; P < 0.001). In conclusion, CD liposome mediated VEGF(165) gene transfer with SkMs effectively induced neovascularization in the ischaemic hind limb and may serve as a safe and new therapeutic modality for the repair of acute ischaemic limb disease.     

Local temperature fine-tunes the timing of spring migration in birds

Evidence for climate-driven phenological changes is rapidly increasing at all trophic levels. Our current poor knowledge of the detailed control of bird migration from the level of genes and hormonal control to direct physiological and behavioral responses hampers our ability to understand and predict consequences of climatic change for migratory birds. In order to better understand migration phenology and adaptation in environmental changes, we here assess the scale at which weather affects timing of spring migration in passerine birds. We use three commonly used proxies of spring-time climatic conditions: (1) vegetation "greenness" (NDVI) in Europe, (2) local spring temperatures in northern Europe, and (3) the North Atlantic Oscillation Index (NAO) as predictors of the phenology of avian migration as well as the strength of their effect on different subsets of populations and the dependence of correlations on species-specific migratory strategy. We analyze phenological patterns of the entire spring migration period in 12 Palaearctic passerine species, drawing on long-term data collected at three locations along a longitudinal gradient situated close to their northern European breeding area. Local temperature was the best single predictor of phenology with the highest explanatory power achieved in combination with NAO. Furthermore, early individuals are more affected by climatic variation compared to individuals on later passage, indicating that climatic change affects subsets of migratory populations differentially. Species wintering closer to the breeding areas were affected more than were those travelling longer distances and this pattern was strongest for the earliest subsets of the population. Overall, our results suggest that at least early subsets of the population are affected by local conditions and early birds use local conditions to fine-tune the date of their spring arrival while individuals arriving later are driven by other factors than local conditions e.g. endogenous control. Understanding what cues migratory organisms use to arrive at an optimum time is important for increasing our knowledge of fundamental issues like decision making in organisms during migration and is crucial for future protection of migratory organisms.     

Distinctive activities of DNA polymerases during human DNA replication

The contributions of human DNA polymerases (pols) alpha, delta and epsilon during S-phase progression were studied in order to elaborate how these enzymes co-ordinate their functions during nuclear DNA replication. Pol delta was three to four times more intensely UV cross-linked to nascent DNA in late compared with early S phase, whereas the cross-linking of pols alpha and epsilon remained nearly constant throughout the S phase. Consistently, the chromatin-bound fraction of pol delta, unlike pols alpha and epsilon, increased in the late S phase. Moreover, pol delta neutralizing antibodies inhibited replicative DNA synthesis most efficiently in late S-phase nuclei, whereas antibodies against pol epsilon were most potent in early S phase. Ultrastructural localization of the pols by immuno-electron microscopy revealed pol epsilon to localize predominantly to ring-shaped clusters at electron-dense regions of the nucleus, whereas pol delta was mainly dispersed on fibrous structures. Pol alpha and proliferating cell nuclear antigen displayed partial colocalization with pol delta and epsilon, despite the very limited colocalization of the latter two pols. These data are consistent with models where pols delta and epsilon pursue their functions at least partly independently during DNA replication.     

Interactions of histone H1 with phospholipids and comparison of its binding to giant liposomes and human leukemic T cells

Due to its net positive charge histone H1 readily associates with liposomes containing acidic phospholipids, such as phosphatidylserine (PS). Interestingly, circular dichroism reveals that while histone H1 in aqueous solutions appears as a random coil, its binding to liposomes containing PS is associated with a pronounced increase in alpha-helicity and beta-sheet content, estimated at 7% and 24%, respectively. This interaction further results in vesicle aggregation and lipid mixing. Fluorescence microscopy revealed rapid binding of Texas Red-labeled H1 (TR-H1) to giant liposomes composed of phosphatidylcholine and PS (SOPC/brain PS, 9/1 molar ratio), followed by lateral segregation and subsequent translocation of the membrane-bound H1 into the giant liposome. The above processes in giant liposomes did depend on the presence of the negatively charged PS. Comparison of the behavior of H1 in giant liposomes to that in cultured leukemic T cells demonstrated very similar patterns. More specifically, fluorescence microscopy revealed binding of TR-H1 to the plasma membrane as lateral segregated microdomains, followed by translocation into the cell. H1 also triggered membrane blebbing and fragmentation of the nuclei of these cells, thus suggesting induction of apoptosis. Our findings indicate that histone H1 and acidic phospholipids form supramolecular aggregates in the plasma membrane of T cells, subsequently resulting in major rearrangements of cellular membranes. Our results allow us to conclude that the minimal requirement for the interaction of histone H1 with the leukemia cell plasma membrane is reproduced by giant liposomes composed of unsaturated phosphatidylcholine and phosphatidylserine, the latter being mandatory for the observed changes in the secondary structure of H1 as well as the macroscopic consequences of the H1-PS interactions.     

Aggressiveness is associated with genetic diversity in landlocked salmon (Salmo salar)

The amount of intraindividual genetic variation has often been found to have profound effects on life history traits. However, studies concerning the relationship between behaviour and genetic diversity are scarce. Aggressiveness is an important component of competitive ability in juvenile salmonids affecting their later performance and survival. In this study, we used an experimental approach to test the prediction that juveniles with low estimated genetic diversity should be less aggressive than juveniles with high estimated genetic diversity in fry from a highly endangered population of land-locked salmon (Salmo salar). This was achieved by using a method enabling the accurate estimation of offspring genetic diversity based on parental microsatellite genotype data. This allowed us to create two groups of offspring expected to have high or low genetic diversity in which aggressive behaviour could be compared. Salmon fry with low estimated genetic diversity were significantly less aggressive than fry with high estimated genetic diversity. Closer analysis of the data suggested that this difference was due to differences in more costly acts of aggression. Our result may reflect a direct effect of genetic variation on a fitness-related trait; however, we cannot rule out an alternative explanation of allele-specific phenotype matching, where lowered aggression is expressed towards genetically more similar individuals.     

Efficient estimation of emission probabilities in profile hidden Markov models

MOTIVATION: Profile hidden Markov models provide a sensitive method for performing sequence database search and aligning multiple sequences. One of the drawbacks of the hidden Markov model is that the conserved amino acids are not emphasized, but signal and noise are treated equally. For this reason, the number of estimated emission parameters is often enormous. Focusing the analysis on conserved residues only should increase the accuracy of sequence database search. RESULTS: We address this issue with a new method for efficient emission probability (EEP) estimation, in which amino acids are divided into effective and ineffective residues at each conserved alignment position. A practical study with 20 protein families demonstrated that the EEP method is capable of detecting family members from other proteins with sensitivity of 98% and specificity of 99% on the average, even if the number of free emission parameters was decreased to 15% of the original. In the database search for TIM barrel sequences, EEP recognizes the family members nearly as accurately as HMMER or Blast, but the number of false positive sequences was significantly less than that obtained with the other methods. AVAILABILITY: The algorithms written in C language are available on request from the authors.     

Photoinhibition and loss of photosystem II reaction centre proteins during senescence of soybean leaves. Enhancement of photoinhibition by the 'stay-green' mutation cytG

The 'stay-green' mutation cytG in soybean ( Glycine max ) partially inhibits the degradation of the light-harvesting complex II (LHCII) and the associated chlorophyll during monocarpic senescence. cytG did not alter the breakdown of the cytochrome b 6/ f complex, thylakoid ATP synthase or components of Photosystem I. In contrast, cytG accelerated the loss of oxygen evolution activity and PSII reaction-centre proteins. These data suggest that LHCII and other thylakoid components are degraded by separate pathways. In leaves induced to senesce by darkness, cytG inhibited the breakdown of LHCII and chlorophyll, but it did not enhance the loss of PSII-core components, indicating that the accelerated degradation of PSII reaction centre proteins in cytG was light dependent. Illumination of mature and senescent leaves of wild-type soybean in the presence of an inhibitor (lincomycin) of chloroplast protein synthesis revealed that senescence per se did not affect the rate of photoinhibition in leaves. Likewise, mature leaves of the cytG mutant did not show more photoinhibition than wild-type leaves. However, in senescent cytG leaves, photoinhibition proceeded more rapidly than in the wild-type. We conclude that the cytG mutation enhances photoinhibition in senescing leaves, and photoinhibition causes the rapid loss of PSII reaction-centre proteins during senescence in cytG .