Ultrafast Red Light Activation of Synechocystis Phytochrome Cph1 Triggers Major Structural Change to Form the Pfr Signalling-Competent State

Phytochromes are dimeric photoreceptors that regulate a range of responses in plants and microorganisms through interconversion of red light-absorbing (Pr) and far-red light-absorbing (Pfr) states. Photoconversion between these states is initiated by light-driven isomerization of a bilin cofactor, which triggers protein structural change. The extent of this change, and how light-driven structural changes in the N-terminal photosensory region are transmitted to the C-terminal regulatory domain to initiate the signalling cascade, is unknown. We have used pulsed electron-electron double resonance (PELDOR) spectroscopy to identify multiple structural transitions in a phytochrome from Synechocystis sp. PCC6803 (Cph1) by measuring distances between nitroxide labels introduced into the protein. We show that monomers in the Cph1 dimer are aligned in a parallel ‘head-to-head’ arrangement and that photoconversion between the Pr and Pfr forms involves conformational change in both the N- and C-terminal domains of the protein. Cryo-trapping and kinetic measurements were used to probe the extent and temporal properties of protein motions for individual steps during photoconversion of Cph1. Formation of the primary photoproduct Lumi-R is not affected by changes in solvent viscosity and dielectric constant. Lumi-R formation occurs at cryogenic temperatures, consistent with their being no major structural reorganization of Cph1 during primary photoproduct formation. All remaining steps in the formation of the Pfr state are affected by solvent viscosity and dielectric constant and occur only at elevated temperatures, implying involvement of a series of long-range solvent-coupled conformational changes in Cph1. We show that signalling is achieved through ultrafast photoisomerization where localized structural change in the GAF domain is transmitted and amplified to cause larger-scale and slower conformational change in the PHY and histidine kinase domains. This hierarchy of timescales and extent of structural change orientates the histidine kinase domain to elicit the desired light-activated biological response.     

An Invasive Fish and the Time-Lagged Spread of Its Parasite across the Hawaiian Archipelago

Efforts to limit the impact of invasive species are frustrated by the cryptogenic status of a large proportion of those species. Half a century ago, the state of Hawai''i introduced the Bluestripe Snapper, Lutjanus kasmira, to O''ahu for fisheries enhancement. Today, this species shares an intestinal nematode parasite, Spirocamallanus istiblenni, with native Hawaiian fishes, raising the possibility that the introduced fish carried a parasite that has since spread to naïve local hosts. Here, we employ a multidisciplinary approach, combining molecular, historical, and ecological data to confirm the alien status of S. istiblenni in Hawai''i. Using molecular sequence data we show that S. istiblenni from Hawai''i are genetically affiliated with source populations in French Polynesia, and not parasites at a geographically intermediate location in the Line Islands. S. istiblenni from Hawai''i are a genetic subset of the more diverse source populations, indicating a bottleneck at introduction. Ecological surveys indicate that the parasite has found suitable intermediate hosts in Hawai''i, which are required for the completion of its life cycle, and that the parasite is twice as prevalent in Hawaiian Bluestripe Snappers as in source populations. While the introduced snapper has spread across the entire 2600 km archipelago to Kure Atoll, the introduced parasite has spread only half that distance. However, the parasite faces no apparent impediments to invading the entire archipelago, with unknown implications for naïve indigenous Hawaiian fishes and the protected Papahānaumokuākea Marine National Monument.     

Identification of an oestrus-associated glycoprotein in oviducal fluid of the sheep

Samples of oviducal fluid were collected daily from sheep with indwelling catheters. Fluid samples taken from both oviducts of 2 sheep for 2 cycles during the middle of the breeding season (April/May) (8 sets of data) were compared with 9 sets of data generated from 2 cycles in 3 sheep later in the breeding season (June/July). Around the period of oestrus, the output of oviducal fluid increased to a peak volume of 1.56 +/- 0.35 ml per day (mean +/- s.d.) compared with a mid-cycle volume of 0.49 +/- 0.29 ml. Later in the breeding season, the flow rates were lower, but showed the same trend (0.91 +/- 0.24 ml at the peak and 0.25 +/- 0.18 ml 7 days later). The total amount of protein secreted by the oviduct each day increased 2-4-fold around the time of oestrus, with higher levels in mid-season ewes. When oviducal fluids were fractionated by SDS electrophoresis, a novel glycoprotein, subunit size of Mr 80-90 000 was identified in samples for 3-6 days of each cycle, coinciding with the period of high fluid flow rate. This protein first appeared in the oviducal fluid on the day of oestrus or the following day and it represented 1 of the 2 major glycoproteins in oviducal fluid as assessed by periodic acid-Schiff (PAS) staining. A PAS-positive protein (Mr 80-90 000) was also detected in fluid taken after oestrus on native highly cross-linked gradient gels after electrophoresis at pH 3.1 but not at pH 8.3. Both gradient gel systems showed an increase in high molecular weight material (Mr greater than 10(6] in fluid taken soon after oestrus.     

Displacement sensors in the honeybee pollen basket

The mechanical importance of different groups of corbicular setae to the formation and maintenance of the pollen load was established through ablation experiments. The neurophysiological characteristics of corbicular setae were investigated and it was found that there are three types of response to mechanical displacement of individual setae. At least some of the anterior corbicular setae behave as linear displacement sensors and are capable of measuring the size of the forming pollen load during foraging.     

Spontaneous Autoimmunity in 129 and C57BL/6 Mice—Implications for Autoimmunity Described in Gene-Targeted Mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE.