The pattern of Dunlin Calidris alpina distribution and abundance in relation to habitat variation in the Flow Country of northern Scotland

Capsule Folivorous caterpillars constituted the majority of nestlings’ food in a primeval forest. Blue Tit broods only partially matched the caterpillar peak, and the mismatch did not affect food composition or nesting success.

Aims To describe factors influencing the timing of reproduction in Blue Tits under primeval conditions (Bia?owie?a National Park, Poland) and to check whether they schedule breeding so as to synchronize broods with a seasonal caterpillar peak.

Methods We gathered information on phenology of leaf development, seasonal availability of folivorous caterpillars (frass collection), timing of Blue Tit breeding, composition of its nestling food, and nest fate over a three-year period.

Results Caterpillars constituted c. 74% of nestling diet, but only 17–65% of broods matched the caterpillar peak in any season. Neither total nest loss, nor frequency of brood reduction depended on the level of mismatch. Caterpillar availability was probably adequate every year, regardless of the amount of mismatch, and no selective advantage of precise matching was detectable. Phenological events at all trophic levels occurred earlier in warmer springs. Egg-laying coincided with tree bud burst and appearance of caterpillars, but was not critically dependent on their timing.

Conclusion The observations are consistent with the view that Blue Tits under primeval conditions in Bia?owie?a National Park, Poland, breed as early as possible, rather than synchronizing their breeding with the caterpillar peak later in the season.     

Assembly of the major light-harvesting complex II in lipid nanodiscs

Self-aggregation of isolated plant light-harvesting complexes (LHCs) upon detergent extraction is associated with fluorescence quenching and is used as an in vitro model to study the photophysical processes of nonphotochemical quenching (NPQ). In the NPQ state, in vivo induced under excess solar light conditions, harmful excitation energy is safely dissipated as heat. To prevent self-aggregation and probe the conformations of LHCs in a lipid environment devoid from detergent interactions, we assembled LHCII trimer complexes into lipid nanodiscs consisting of a bilayer lipid matrix surrounded by a membrane scaffold protein (MSP). The LHCII nanodiscs were characterized by fluorescence spectroscopy and found to be in an unquenched, fluorescent state. Remarkably, the absorbance spectra of LHCII in lipid nanodiscs show fine structure in the carotenoid and Q_y region that is different from unquenched, detergent-solubilized LHCII but similar to that of self-aggregated, quenched LHCII in low-detergent buffer without magnesium ions. The nanodisc data presented here suggest that 1), LHCII pigment-protein complexes undergo conformational changes upon assembly in nanodiscs that are not correlated with downregulation of its light-harvesting function; and 2), these effects can be separated from quenching and aggregation-related phenomena. This will expand our present view of the conformational flexibility of LHCII in different microenvironments.     

Myofiber integrity depends on desmin network targeting to Z-disks and costameres via distinct plectin isoforms

Dysfunction of plectin, a 500-kD cytolinker protein, leads to skin blistering and muscular dystrophy. Using conditional gene targeting in mice, we show that plectin deficiency results in progressive degenerative alterations in striated muscle, including aggregation and partial loss of intermediate filament (IF) networks, detachment of the contractile apparatus from the sarcolemma, profound changes in myofiber costameric cytoarchitecture, and decreased mitochondrial number and function. Analysis of newly generated plectin isoform-specific knockout mouse models revealed that IF aggregates accumulate in distinct cytoplasmic compartments, depending on which isoform is missing. Our data show that two major plectin isoforms expressed in muscle, plectin 1d and 1f, integrate fibers by specifically targeting and linking desmin IFs to Z-disks and costameres, whereas plectin 1b establishes a linkage to mitochondria. Furthermore, disruption of Z-disk and costamere linkages leads to the pathological condition of epidermolysis bullosa with muscular dystrophy. Our findings establish plectin as the major organizer of desmin IFs in myofibers and provide new insights into plectin- and desmin-related muscular dystrophies.     

Analysis of FRET signals in the presence of free donors and acceptors

A method for spectral analysis of Förster resonance energy transfer (FRET) signals is presented, taking into consideration both the contributions of unpaired donor and acceptor fluorophores and the influence of incomplete labeling of the interacting partners. It is shown that spectral analysis of intermolecular FRET cannot yield accurate values of the Förster energy transfer efficiency E, unless one of the interactors is in large excess and perfectly labeled. Instead, analysis of donor quenching yields a product of the form Ef_dp_a, where f_d is the fraction of donor-type molecules participating in donor-acceptor complexes and p_a is the labeling probability of the acceptor. Similarly, analysis of sensitized emission yields a product involving Ef_a. The analysis of intramolecular FRET (e.g., of tandem constructs) yields the product Ep_a. We use our method to determine these values for a tandem construct of cyan fluorescent protein and yellow fluorescent protein and compare them with those obtained by standard acceptor photobleaching and fluorescence lifetime measurements. We call the method lux-FRET, since it relies on linear unmixing of spectral components.     

Comparative characterization of repABC-type replicons of Paracoccus pantotrophus composite plasmids

The repABC replicons have an unusual structure, since they carry genes coding for partitioning (repA, repB) and replication (repC) proteins, which are organized in an operon. So far, the presence of these compact bi-functional modules has been reported only in the megaplasmids of the Rhizobiaceae and within the plasmid pTAV1 (107kb) of Paracoccus versutus. We studied the distribution of repABC-type replicons within bacteria belonging to the genus Paracoccus. We found that repABC replicons occur only in the group of pTAV1-like plasmids: pKLW1, pHG16-a, pWKS2, and pPAN1, harbored by different strains of Paracoccus pantotrophus. A partial sequencing approach followed by phylogenetic analysis revealed that these replicons constitute a distinct evolutionary branch of repABC replicons. Incompatibility studies showed that they represent two incompatibility groups designated IncABC1 (pTAV1, pKLW1, and pHG16-a) and IncABC2 (pPAN1). Sequence comparison using available databases allowed the identification, within plasmid pRS241d of Rhodobacter sphaeroides 2.4.1, of an additional sequence highly homologous to the paracoccal repABC replicons, which has been included in comparative analyses.