A gain-of-function mutation of Arabidopsis cryptochrome1 promotes flowering

Plants use different classes of photoreceptors to collect information about their light environment. Cryptochromes are blue light photoreceptors that control deetiolation, entrain the circadian clock, and are involved in flowering time control. Here, we describe the cry1-L407F allele of Arabidopsis (Arabidopsis thaliana), which encodes a hypersensitive cryptochrome1 (cry1) protein. Plants carrying the cry1-L407F point mutation have elevated expression of CONSTANS and FLOWERING LOCUS T under short-day conditions, leading to very early flowering. These results demonstrate that not only the well-studied cry2, with an unequivocal role in flowering promotion, but also cry1 can function as an activator of the floral transition. The cry1-L407F mutants are also hypersensitive toward blue, red, and far-red light in hypocotyl growth inhibition. In addition, cry1-L407F seeds are hypersensitive to germination-inducing red light pulses, but the far-red reversibility of this response is not compromised. This demonstrates that the cry1-L407F photoreceptor can increase the sensitivity of phytochrome signaling cascades. Molecular dynamics simulation of wild-type and mutant cry1 proteins indicated that the L407F mutation considerably reduces the structural flexibility of two solvent-exposed regions of the protein, suggesting that the hypersensitivity might result from a reduced entropic penalty of binding events during downstream signal transduction. Other nonmutually exclusive potential reasons for the cry1-L407F gain of function are the location of phenylalanine-407 close to three conserved tryptophans, which could change cry1's photochemical properties, and stabilization of ATP binding, which could extend the lifetime of the signaling state of cry1.     

Socio-Spatial Relationships in Dairy Cows

Farm animals may serve as models for evaluating social networks in a controlled environment. We used an automated system to track, at fine temporal and spatial resolution (once per minute, ±50 cm) every individual in six herds of dairy cows ( Bos taurus ). We then analysed the data using social network analyses. Relationships were based on non-random attachment and avoidance relationships in respect to synchronous use and distances observed in three different functional areas (activity, feeding and lying). We found that neither synchrony nor distance between cows was strongly predictable among the three functional areas. The emerging social networks were tightly knit for attachment relationships and less dense for avoidance relationships. These networks loosened up from the feeding and lying area to the activity area, and were less dense for relationships based on synchronicity than on median distance with respect to node degree, relative size of the largest cluster, density and diameter of the network. In addition, synchronicity was higher in dyads of dairy cows that had grown up together and shared their last dry period. This last effect disappeared with increasing herd size. Dairy herds can be characterized by one strongly clustered network including most of the herd members with many non-random attachment and avoidance relationships. Closely synchronous dyads were composed of cows with more intense previous contact. The automatic tracking of a large number of individuals proved promising in acquiring the data necessary for tackling social network analyses.     

Increasingly ice-free winters and their effects on water quality in Sweden’s largest lakes

Mean global air temperatures have steadily increased during recent decades, resulting in an earlier timing of lake ice breakup. In Sweden’s largest lakes, Vänern and Vättern, the breakup of ice has occurred considerably earlier since 1979 and ice-free winters have become more frequent. Comparison between the years when the lakes were ice covered with those when they remained ice-free in terms of 37 lake variables revealed significant differences in water temperatures, sulphate concentrations and the biomass of diatoms in May after ice breakup (P < 0.01). In particular, the biomass of the genus Aulacoseira increased significantly, which may explain increasing complaints about algae that clog fishing-nets, filter-beds and micro-strainers in waterworks in Vänern and Vättern. We assume that Aulacoseira is mainly affected by changes in climate-driven water circulation patterns. In contrast, other observed water quality changes such as changes in sulphate concentration might rather be attributed to changes in atmospheric deposition. To explain water quality changes in Sweden’s largest lakes it is important to consider changes in both climate and atmospheric deposition as well as catchment measures.     

Drei neue Polychaeten-Arten der Familien Polynoidae und Syllidae von Neu-Kaledonien,assoziiert mit einer verkalkten Hydrozoe

Three new species are described:Lagisca zibrowii (Polynoidae) andProcerastea hydrozoicola andP. parasimpliseta (Syllidae), living in association with a calcified hydrozoan, probably of the genusPseudosolanderia (Rosalindidae). The genusParaprocerastea is synonymized withProcerastea.     

Myelin Membrane Assembly Is Driven by a Phase Transition of Myelin Basic Proteins Into a Cohesive Protein Meshwork

Rapid conduction of nerve impulses requires coating of axons by myelin. To function as an electrical insulator, myelin is generated as a tightly packed, lipid-rich multilayered membrane sheath. Knowledge about the mechanisms that govern myelin membrane biogenesis is required to understand myelin disassembly as it occurs in diseases such as multiple sclerosis. Here, we show that myelin basic protein drives myelin biogenesis using weak forces arising from its inherent capacity to phase separate. The association of myelin basic protein molecules to the inner leaflet of the membrane bilayer induces a phase transition into a cohesive mesh-like protein network. The formation of this protein network shares features with amyloid fibril formation. The process is driven by phenylalanine-mediated hydrophobic and amyloid-like interactions that provide the molecular basis for protein extrusion and myelin membrane zippering. These findings uncover a physicochemical mechanism of how a cytosolic protein regulates the morphology of a complex membrane architecture. These results provide a key mechanism in myelin membrane biogenesis with implications for disabling demyelinating diseases of the central nervous system.     

CTL escape mediated by proteasomal destruction of an HIV-1 cryptic epitope

Cytotoxic CD8+ T cells (CTLs) play a critical role in controlling viral infections. HIV-infected individuals develop CTL responses against epitopes derived from viral proteins, but also against cryptic epitopes encoded by viral alternative reading frames (ARF). We studied here the mechanisms of HIV-1 escape from CTLs targeting one such cryptic epitope, Q9VF, encoded by an HIVgag ARF and presented by HLA-B*07. Using PBMCs of HIV-infected patients, we first cloned and sequenced proviral DNA encoding for Q9VF. We identified several polymorphisms with a minority of proviruses encoding at position 5 an aspartic acid (Q9VF/5D) and a majority encoding an asparagine (Q9VF/5N). We compared the prevalence of each variant in PBMCs of HLA-B*07+ and HLA-B*07- patients. Proviruses encoding Q9VF/5D were significantly less represented in HLA-B*07+ than in HLA-B*07- patients, suggesting that Q9FV/5D encoding viruses might be under selective pressure in HLA-B*07+ individuals. We thus analyzed ex vivo CTL responses directed against Q9VF/5D and Q9VF/5N. Around 16% of HLA-B*07+ patients exhibited CTL responses targeting Q9VF epitopes. The frequency and the magnitude of CTL responses induced with Q9VF/5D or Q9VF/5N peptides were almost equal indicating a possible cross-reactivity of the same CTLs on the two peptides. We then dissected the cellular mechanisms involved in the presentation of Q9VF variants. As expected, cells infected with HIV strains encoding for Q9VF/5D were recognized by Q9VF/5D-specific CTLs. In contrast, Q9VF/5N-encoding strains were neither recognized by Q9VF/5N- nor by Q9VF/5D-specific CTLs. Using in vitro proteasomal digestions and MS/MS analysis, we demonstrate that the 5N variation introduces a strong proteasomal cleavage site within the epitope, leading to a dramatic reduction of Q9VF epitope production. Our results strongly suggest that HIV-1 escapes CTL surveillance by introducing mutations leading to HIV ARF-epitope destruction by proteasomes.