Can the failure to punish promote cheating in mutualism?

A key challenge in the study of mutualism is to understand the mechanisms that prevent cheating. In some systems, host retaliation against cheaters prevents the breakdown of cooperation. Here, we focus on the converse of this demonstration, and ask whether hosts that fail to retaliate are commonly inhabited by cheaters. We do so using the classic ant–plant interaction, in which plants provide ant-housing (domatia) in return for protection from herbivores. Our model system is the rattan ant-palm Korthalsia furtadoana , which grows swollen leaf sheaths as domatia and associates with two species of obligate host-ants, Camponotus sp90 and C. sp93 , and with facultative Crematogaster and 'tramp' ant species. One ant-tree species is known to retaliate by tying the growth of domatia to the successful protection of new leaves, and non-protecting cheaters are rare. In contrast, K. furtadoana grows the domatium before the new leaf develops, suggesting that sanctioning may not be possible. We experimentally simulated herbivory by cutting leaves from shoots and found no difference in the mortality and growth of domatia on such 'cheated' shoots than on controls, confirming that K. furtadoana cannot sanction non-protectors. We then investigated the intensity of protection that Camponotus and Crematogaster ant-symbionts provide K. furtadoana . We demonstrate that C. sp90 , which only inhabit half of colonised plants, vigorously protects leaves, that C. sp93 rarely protects, and that Crematogaster never protects. We then show that plants inhabited by C. sp90 have a higher growth rate than those inhabited by C. sp93 . We conclude that C. sp90 is a protection mutualist, while C. sp93 and Crematogaster are parasites, the first such demonstrations for an ant–palm interaction. The presence of commonly occurring parasites, as well as rare tramp ants, provides the first clear correlative evidence that an inability to punish results in abundant cheating.     

The structural basis of the TIM10 chaperone assembly

Tim9 and Tim10 are essential components of the "small Tim" family of proteins that facilitate insertion of polytopic proteins at the inner mitochondrial membrane. The small Tims are themselves imported from the cytosol and are organized in specific translocation assemblies in the intermembrane space. Their conformational properties and how these influence the mechanism of assembly remain poorly understood. Moreover, the three-dimensional structure of the TIM10 complex is unknown. We have characterized the structural properties of these proteins in their free and assembled states using NMR, circular dichroism, and small angle x-ray scattering. We show that the free proteins are largely unfolded in their reduced assembly-incompetent state and molten globules in their oxidized assembly-competent state. Tim10 appears less structured than Tim9 in their respective free oxidized forms and undergoes a larger structural change than Tim9 upon complexation. The NMR data here demonstrates unequivocally that only the oxidized states of the Tim9 and Tim10 proteins are capable of forming a complex. Zinc binding stabilizes the reduced state against proteolysis without significantly affecting the secondary structure. Solution x-ray scattering was used to obtain a molecular envelope for the subunits individually and for their fully functional TIM10 complex. Ab initio shape reconstructions based on the scattering data has allowed us to obtain the first low resolution three-dimensional structure of the TIM10 complex. This is a novel structure that displays extensive surface hydrophobicity. The structure also provides an explanation for the escorting function of this non-ATP-powered chaperone particle.     

Requirement of the proteasome for the trimming of signal peptide-derived epitopes presented by the nonclassical major histocompatibility complex class I molecule HLA-E

The nonclassical major histocompatibility complex class I molecule HLA-E acts as a ligand for CD94/NKG2 receptors on the surface of natural killer cells and a subset of T cells. HLA-E presents closely related nonameric peptide epitopes derived from the highly conserved signal sequences of classical major histocompatibility complex class I molecules as well as HLA-G. Their generation requires cleavage of the signal sequence by signal peptidase followed by the intramembrane-cleaving aspartic protease, signal peptide peptidase. In this study, we have assessed the subsequent proteolytic requirements leading to generation of the nonameric HLA-E peptide epitopes. We show that proteasome activity is required for further processing of the peptide generated by signal peptide peptidase. This constitutes the first example of capture of a naturally derived short peptide by the proteasome, producing a class I peptide ligand.     

Predation risk and inter-population variation in antipredator behaviour in the three-spined stickleback, Gasterosteus aculeatus L.

Predation risk from fish and bird predators was assessed at seven Scottish Gasterosteus aculeatus L. sites. Samples of adult male and female sticklebacks and fry from each site were tested with either a model heron or a live pike to measure anti-predator responses. Principal Component Analyses were then used to describe the responses, the first factor to emerge from each multivariate analysis providing an index of overall level of response toward the predator. Significant sexual and inter-population differences in behaviour are described. Sticklebacks from populations at high risk from either predatory fish or birds showed higher fright response scores than fish from low risk sites. In general, adult male sticklebacks are bolder than adult females during interactions with predators.     

Brood Value and Life Expectancy as Determinants of Parental Investment in Male Three-spined Sticklebacks,Gasterosteus aculeatus

29 breeding male three-spined sticklebacks (Gasterosteus aculeatus) caught in the wild at different times in the breeding season were exposed simultaneously to a potential threat to their nest (a conspecific male) and to two hunting trout (potential predators of adult sticklebacks, seen through a transparent partition). By promoting a variety of protective responses, the presence of the predators reduced both the time spent confronting the intruder and the rate at which it was attacked. Subjects with a clutch of eggs in their nest maintained higher levels of territorial defence in the presence of predators than did those with an empty nest. However, those breeding later in the season took fewer risks to defend their nest. Possible proximate mechanisms responsible for these results are discussed. In addition, the adaptive significance of the behavioural changes is considered in the light of the value of the brood and the expected future reproductive output of the sticklebacks breeding at different times in the season.     

Histopathological Studies of Resistance of Sunflower (Helianthus annuus L.) to Downy Mildew (Plasmopara halstedii)

Histopathological studies of the infection of sunflower seedlings by downy mildew ( Plasmopara halstedii ) have shown that penetration of roots and the lower part of the hypocotyl occurs for both compatible combinations (suseptibility) and incompatible combinations (resistance). After penetrating susceptible genotypes, the parasite develops intercellular hyphae and intracellular haustoria, leading to systemic invasion. In contrast, in resistant plants, as soon as colonization develops, hypersensitive-like reactions occur in the parenchyma, with the appearance of necrotic zones surrounded by dividing cells. Growth of the parasite is strongly inhibited and most hyphae are blocked before they reach the cotyledonary node.     

Suppression of inflammatory arthritis by the parasitic worm product ES-62 is associated with epigenetic changes in synovial fibroblasts

ES-62 is the major secreted protein of the parasitic filarial nematode, Acanthocheilonema viteae. The molecule exists as a large tetramer (MW, ~240kD), which possesses immunomodulatory properties by virtue of multiple phosphorylcholine (PC) moieties attached to N-type glycans. By suppressing inflammatory immune responses, ES-62 can prevent disease development in certain mouse models of allergic and autoimmune conditions, including joint pathology in collagen-induced arthritis (CIA), a model of rheumatoid arthritis (RA). Such protection is associated with functional suppression of “pathogenic” hyper-responsive synovial fibroblasts (SFs), which exhibit an aggressive inflammatory and bone-damaging phenotype induced by their epigenetic rewiring in response to the inflammatory microenvironment of the arthritic joint. Critically, exposure to ES-62 in vivo induces a stably-imprinted CIA-SF phenotype that exhibits functional responses more typical of healthy, Naïve-SFs. Consistent with this, ES-62 “rewiring” of SFs away from the hyper-responsive phenotype is associated with suppression of ERK activation, STAT3 activation and miR-155 upregulation, signals widely associated with SF pathogenesis. Surprisingly however, DNA methylome analysis of Naïve-, CIA- and ES-62-CIA-SF cohorts reveals that rather than simply preventing pathogenic rewiring of SFs, ES-62 induces further changes in DNA methylation under the inflammatory conditions pertaining in the inflamed joint, including targeting genes associated with ciliogenesis, to programme a novel “resolving” CIA-SF phenotype. In addition to introducing a previously unsuspected aspect of ES-62’s mechanism of action, such unique behaviour signposts the potential for developing DNA methylation signatures predictive of pathogenesis and its resolution and hence, candidate mechanisms by which novel therapeutic interventions could prevent SFs from perpetuating joint inflammation and destruction in RA. Pertinent to these translational aspects of ES-62-behavior, small molecule analogues (SMAs) based on ES-62’s active PC-moieties mimic the rewiring of SFs as well as the protection against joint disease in CIA afforded by the parasitic worm product.     

In Vivo Assessment of Bone Regeneration in Alginate/Bone ECM Hydrogels with Incorporated Skeletal Stem Cells and Single Growth Factors

The current study has investigated the use of decellularised, demineralised bone extracellular matrix (ECM) hydrogel constructs for in vivo tissue mineralisation and bone formation. Stro-1-enriched human bone marrow stromal cells were incorporated together with select growth factors including VEGF, TGF-β3, BMP-2, PTHrP and VitD3, to augment bone formation, and mixed with alginate for structural support. Growth factors were delivered through fast (non-osteogenic factors) and slow (osteogenic factors) release PLGA microparticles. Constructs of 5 mm length were implanted in vivo for 28 days within mice. Dense tissue assessed by micro-CT correlated with histologically assessed mineralised bone formation in all constructs. Exogenous growth factor addition did not enhance bone formation further compared to alginate/bone ECM (ALG/ECM) hydrogels alone. UV irradiation reduced bone formation through degradation of intrinsic growth factors within the bone ECM component and possibly also ECM cross-linking. BMP-2 and VitD3 rescued osteogenic induction. ALG/ECM hydrogels appeared highly osteoinductive and delivery of angiogenic or chondrogenic growth factors led to altered bone formation. All constructs demonstrated extensive host tissue invasion and vascularisation aiding integration and implant longevity. The proposed hydrogel system functioned without the need for growth factor incorporation or an exogenous inducible cell source. Optimal growth factor concentrations and spatiotemporal release profiles require further assessment, as the bone ECM component may suffer batch variability between donor materials. In summary, ALG/ECM hydrogels provide a versatile biomaterial scaffold for utilisation within regenerative medicine which may be tailored, ultimately, to form the tissue of choice through incorporation of select growth factors.     

Surgical anatomy of the levator veli palatini: a previously undescribed tendinous insertion of the anterolateral fibers

The purpose of this study was to describe the previously unreported tendinous insertion of the anterolateral fibers of the levator veli palatini (levator) and discuss possible implications for levator function and cleft palate repair. The velopharyngeal anatomy in normal adult cadavers was studied, with histologic confirmation of anatomical findings. These findings were compared with a more limited study of levator anatomy in cleft palates at the time of intraoperative muscle dissection. Just before entering the velum, the levator divides into two parts. The smaller bundle of muscle fibers (anterolateral part) runs anteriorly, close to the lateral pharyngeal wall, and inserts into the palatine aponeurosis through a number of fine tendons. The main part of the muscle runs medially into the velum, where it fans out and forms the levator sling with the contralateral levator. The possible function of the anterolateral part of the levator is discussed. Inadequate release of the tendinous insertions at the time of palate repair may tether the levator anteriorly and compromise muscle retropositioning or may result in splitting of the levator, so that only part of the levator is retropositioned.     

Holographic glucose sensors

A novel holographic sensor system capable of detecting dynamic changes in glucose concentration has been developed. The hologram is recorded within a bio-compatible hydrogel matrix containing phenylboronic acid derivatives. On binding glucose, the colour of the hologram red-shifts to longer wavelengths as the hydrogel expands and this colour change is used to quantify glucose concentration. However, phenylboronic acids are non-selective and bind a wide variety of cis-diols. In blood, glucose is the only sugar found free at high concentration, whilst other sugars are typically found as part of glycoproteins and macromolecular structures. Although glycoproteins have been shown to have no effect on the sensor, phenylboronic acids can bind lactate much more readily than glucose. We have designed two polymer hydrogel systems to increase the selectivity of the sensor for glucose over lactate. The first involved the use of high concentrations of 3-acrylamidophenylboronic acid (3-APB) whilst the second system utilised 2-acrylamido-5-fluorophenylboronic acid (5-F-2-MAPB). Both systems displayed an increased selectivity to glucose over lactate at physiological pH and ionic strength and could be deployed as selective holographic sensors for glucose detection in physiological fluids.