Musculature of Seison nebaliae Grube, 1861 and Paraseison annulatus (Claus, 1876) revealed with CLSM: a comparative study of the gnathiferan key taxon Seisonacea (Rotifera)

The somatic muscular systems of two species of Seisonacea (Rotifera), Seison nebaliae and Paraseison annulatus, are described using fluorescently labelled phalloidin in combination with confocal laser scanning microscopy. Their overall muscular arrangement is similar and consists of segmentally organised longitudinal fibres that extend the length of the body and are surrounded by semi-circular (= incomplete) bands. However, differences in the musculature between the two species are present and possibly reflect specific adaptations in feeding strategy and locomotion related to the occupation of individual niches on their host, the leptostracan crustacean N. bipes. For example, S. nebaliae has semi-circular muscles in the head region only, while P. annulatus possesses incomplete circular muscles also in the trunk region; furthermore, there are also differences in the arrangements and number of longitudinal muscles. The muscular systems of all rotifer species examined so far are compared in order to establish the ground pattern of the last putative ancestor as well as to seek for traits of systematic importance. Results from both species corroborate earlier hypotheses on the arrangement of muscles in the putative common ancestor of Rotifera, which suggested an orthogonal arrangement consisting of a series of probably continuous (not segmental) inner longitudinal muscles, surrounded by semi-circular fibres, ventrally opened. However, significant morphological and ecological variations among taxa investigated so far show that a consistent correlation between muscular traits and specific ecological features and/or phylogeny is still far from being clear. Hence, musculature of additional taxa, representing the systematic width and occupying a diverse range of habitats, should be investigated.     

Codanin-1, mutated in the anaemic disease CDAI, regulates Asf1 function in S-phase histone supply

Efficient supply of new histones during DNA replication is critical to restore chromatin organization and maintain genome function. The histone chaperone anti-silencing function 1 (Asf1) serves a key function in providing H3.1-H4 to CAF-1 for replication-coupled nucleosome assembly. We identify Codanin-1 as a novel interaction partner of Asf1 regulating S-phase histone supply. Mutations in Codanin-1 can cause congenital dyserythropoietic anaemia type I (CDAI), characterized by chromatin abnormalities in bone marrow erythroblasts. Codanin-1 is part of a cytosolic Asf1-H3.1-H4-Importin-4 complex and binds directly to Asf1 via a conserved B-domain, implying a mutually exclusive interaction with the chaperones CAF-1 and HIRA. Codanin-1 depletion accelerates the rate of DNA replication and increases the level of chromatin-bound Asf1, suggesting that Codanin-1 guards a limiting step in chromatin replication. Consistently, ectopic Codanin-1 expression arrests S-phase progression by sequestering Asf1 in the cytoplasm, blocking histone delivery. We propose that Codanin-1 acts as a negative regulator of Asf1 function in chromatin assembly. This function is compromised by two CDAI mutations that impair complex formation with Asf1, providing insight into the molecular basis for CDAI disease.     

Mechanism for activation of the growth factor-activated AGC kinases by turn motif phosphorylation

The growth factor/insulin-stimulated AGC kinases share an activation mechanism based on three phosphorylation sites. Of these, only the role of the activation loop phosphate in the kinase domain and the hydrophobic motif (HM) phosphate in a C-terminal tail region are well characterized. We investigated the role of the third, so-called turn motif phosphate, also located in the tail, in the AGC kinases PKB, S6K, RSK, MSK, PRK and PKC. We report cooperative action of the HM phosphate and the turn motif phosphate, because it binds a phosphoSer/Thr-binding site above the glycine-rich loop within the kinase domain, promoting zipper-like association of the tail with the kinase domain, serving to stabilize the HM in its kinase-activating binding site. We present a molecular model for allosteric activation of AGC kinases by the turn motif phosphate via HM-mediated stabilization of the alphaC helix. In S6K and MSK, the turn motif phosphate thereby also protects the HM from dephosphorylation. Our results suggest that the mechanism described is a key feature in activation of upto 26 human AGC kinases.     

Female-limited X-chromosome evolution effects on male pre- and post-copulatory success

Intralocus sexual conflict arises when the expression of shared alleles at a single locus generates opposite fitness effects in each sex (i.e. sexually antagonistic alleles), preventing each sex from reaching its sex-specific optimum. Despite its importance to reproductive success, the relative contribution of intralocus sexual conflict to male pre- and post-copulatory success is not well-understood. Here, we used a female-limited X-chromosome (FLX) evolution experiment in Drosophila melanogaster to limit the inheritance of the X-chromosome to the matriline, eliminating possible counter-selection in males and allowing the X-chromosome to accumulate female-benefit alleles. After more than 100 generations of FLX evolution, we studied the effect of the evolved X-chromosome on male attractiveness and sperm competitiveness. We found a non-significant increase in attractiveness and decrease in sperm offence ability in males expressing the evolved X-chromosomes, but a significant increase in their ability to avoid displacement by other males'' sperm. This is consistent with a trade-off between these traits, perhaps mediated by differences in body size, causing a small net reduction in overall male fitness in the FLX lines. These results indicate that the X-chromosome in D. melanogaster is subject to selection via intralocus sexual conflict in males.     

Extra-pair paternity in relation to regional and local climate in an Arctic-breeding passerine

Reproductive processes are affected by local and regional climate variation. Birds breeding in the Arctic may experience strong energetic constraints, which will affect their reproductive output. Recent research has emphasized the importance of extra-pair copulation as a means of improving reproductive output. In this paper, we explore ecological and climatic determinants that may explain variation in extra-pair paternity (EPP) in an arctic-breeding passerine, the snow bunting Plectrophenax nivalis. EPP occurred in 10.8 % of the young and 20.9 % of the broods sampled from 1999 to 2003. We found that the proportion of extra-pair young in a nest was positively related to the body size and age of the social male and weakly negatively related to the local average minimum temperature prior to the onset of egg laying. These results suggest that older and larger males lost a larger share of paternity than smaller and younger males, and that the relative loss of paternity decreased with cold weather during the female’s fertile period. Large and old males spend less time mate guarding compared to small and young males and may allocate more time towards extra-pair forays, and thus lose more paternity in their own nest. Climatic conditions most likely constrain the total energy budget with less energy available for extra-pair activity in cold weather.     

Elucidating the mechanisms of protein antigen adsorption to the CAF/NAF liposomal vaccine adjuvant systems: Effect of charge,fluidity and antigen-to-lipid ratio

The reverse vaccinology approach has recently resulted in the identification of promising protein antigens, which in combination with appropriate adjuvants can stimulate customized, protective immune responses. Although antigen adsorption to adjuvants influences vaccine efficacy and safety, little is generally known about how antigens and adjuvants interact at the molecular level. The aim of this study was to elucidate the mechanisms of interactions between the equally sized, but oppositely charged model protein antigens α-lactalbumin and lysozyme, and i) the clinically tested cationic liposomal adjuvant CAF01 composed of cationic dimethyldioctadecylammonium (DDA) bromide and trehalose-6,6′-dibehenate (TDB) or ii) the neutral adjuvant formulation NAF01, where DDA was replaced with zwitterionic distearoylphosphatidylcholine (DSPC). The effect of liposome charge, bilayer rigidity, isoelectric point and antigen-to-lipid ratio was investigated using dynamic light scattering, transmission electron microscopy, differential scanning calorimetry, intrinsic fluorescence and Langmuir monolayers. The net anionic α-lactalbumin adsorbed onto the cationic liposomes, while there was no measureable attractive interaction with the zwitterionic liposomes. In contrast, the net cationic lysozyme showed very little interaction with either types of liposome. Adsorption of α-lactalbumin altered its tertiary structure, affected lipid membrane packing below and above the phase transition temperature, and neutralized the liposomal surface charge, resulting in reduced colloidal stability and liposome aggregation. Langmuir studies revealed that α-lactalbumin was not squeezed out of DDA monolayers upon compression, which suggests additional hydrophobic interactions.     

Thioredoxin Txnl1/TRP32 Is a Redox-active Cofactor of the 26 S Proteasome

The 26 S proteasome is a large proteolytic machine, which degrades most intracellular proteins. We found that thioredoxin, Txnl1/TRP32, binds to Rpn11, a subunit of the regulatory complex of the human 26 S proteasome. Txnl1 is abundant, metabolically stable, and widely expressed and is present in the cytoplasm and nucleus. Txnl1 has thioredoxin activity with a redox potential of about-250 mV. Mutant Txnl1 with one active site cysteine replaced by serine formed disulfide bonds to eEF1A1, a substrate-recruiting factor of the 26 S proteasome. eEF1A1 is therefore a likely physiological substrate. In response to knockdown of Txnl1, ubiquitin-protein conjugates were moderately stabilized. Hence, Txnl1 is the first example of a direct connection between protein reduction and proteolysis, two major intracellular protein quality control mechanisms.Degradation of proteins in eukaryotic cells plays a pivotal role in the regulation of several important processes, including cell division, antigen presentation, and signal transduction (1). Most intracellular proteins are degraded by the 26 S proteasome, a 2.5-MDa protease complex composed of more than 30 different subunits (2).To become degraded, proteins are typically first conjugated to a chain of ubiquitin moieties. This reaction is catalyzed by ubiquitin ligases. The ubiquitin chains lend the proteins affinity for the 26 S proteasome (3). For efficient degradation, certain ubiquitylated proteins are shuttled to the 26 S proteasome by substrate recruiting factors, such as Rad23, Dsk2, and eEF1A (4, 5).The 26 S proteasome is composed of two stable subcomplexes, the proteolytically active 20 S core and 19 S regulatory complexes, which bind to one or both ends of the cylindrical 20 S core particle (6). The regulatory complexes first recognize the ubiquitylated substrates (3), before the substrates are deubiquitylated (7, 8), unfolded (9, 10), and translocated into the 20 S particle for degradation.Although the 26 S proteasome has been known for more than 20 years (11), novel subunits and cofactors have been described recently (12, 13). Here we report another novel proteasome-associated protein, Txnl1 (thioredoxin-like protein 1), that associates directly with the proteasome subunit Rpn11. Txnl1 exhibits thioredoxin activity and targets eEF1A1 in vivo. Previous reports have shown that eEF1A1 transfers misfolded nascent proteins from the ribosome to the 26 S proteasome for degradation (5, 14, 15). Accordingly, ubiquitin-protein conjugates were stabilized upon knockdown of Txnl1 expression. Txnl1 therefore directly links protein reduction and proteolysis, two major intracellular protein quality control mechanisms.     

CLSM analysis of the phalloidin-stained muscle system in Nerilla antennata, Nerillidium sp. and Trochonerilla mobilis (Polychaeta; Nerillidae)

The entire muscle system of Nerilla antennata, Nerillidium sp. and Trochonerilla mobilis was three-dimensionally reconstructed from whole mounts. In juvenile and adult specimens the F-actin musculature subset was stained with FITC-conjugated phalloidin and visualized with a confocal laser scanning microscope (cLSM). The muscle system shows the following major organization: 1) circular muscles are totally absent in the body wall; 2) the longitudinal muscles are confined in two ventral and two dorsal thick bundles; 3) additional longitudinal muscles are located in the ventro- and dorsomedian axis; 4) three segmental pairs of ventral oblique muscles elongate into the periphery: the main dorsoventral muscles that run along the body side posterior and dorsally and the anterior and posterior oblique parapodial muscles, which contribute to the ventral chaetal sacs; 5) one segmental pair of dorsal oblique parapodial muscles, contributing to the dorsal chaetal sacs; 6) five to seven small dorsoventral muscles per segment; and 7) complex head and pharyngeal musculature. These results support the belief that absence of circular muscles in the polychaete body wall is much more widely distributed than is currently presumed.     

Ontogenetic- and condition-related effects of starvation on responsiveness in herring larvae (Clupea harengus L.) during repeated attacks by a model predator

The escape behaviour of fed and food-deprived herring larvae (20-30 mm SL) was studied during repeated attacks with a glass probe in order to investigate the causal mechanisms of starvation-induced changes in reaction to predators. Two experiments were set up: one where the fed and starved larvae were of the same age but of different sizes and one with groups of similar size but different ages. Biochemical and morphological condition measures described the condition of individual larvae. Starved larvae showed a lower responsiveness than fed larger larvae of the same age, and the responsiveness in this experiment decreased with decreasing nutritional status of the larvae. However, starved larvae that were of the same size but older than fed larvae showed a higher responsiveness, which could be explained by differences in development of sensory systems. A combination of condition and developmental factors thus explained the differences between starved and fed larvae. Both starved and fed larvae showed decreasing responsiveness over time with repeated attacks with no difference between starved and fed larvae in the relative change over time. The results emphasise the importance of taking into account individual age and/or development when the nutritional condition of wild-caught larvae is incorporated in survival models.