Timing of fledging is influenced by glucocorticoid physiology in Laysan Albatross chicks

Fledging is a major life transition for birds, when juveniles move from the safety of a nest into an environment where they must find food and avoid predators. The timing of fledging within a season can have significant effects on future survival and breeding success. Proximate triggers of fledging are unknown: though wing development is likely a primary factor, other physiological changes, such as elevated plasma corticosterone (CORT), may affect fledging behavior. Laysan Albatross (Phoebastria immutabilis) chicks have an extended post−hatching period during which they reach 150% of adult mass. However, approaching fledging, chicks fast for days to weeks and lose mass while still putting energy into feather growth. We evaluated chick morphology and physiology to elucidate proximate triggers of fledging. As in some other species, CORT increased as chicks fasted and lost body mass. At the same time, corticosteroid binding globulin (CBG) declined, thus amplifying free CORT prior to fledging. Once chicks reached a morphological threshold, free CORT levels predicted how long they stayed at the colony: chicks with higher free CORT fledged sooner. To perturb the relationship between body condition, endocrine physiology, and fledging behavior, we supplementally fed chicks for the month before fledging. Fed birds had a slower decrease in body mass, slower decrease in CBG, slower increase in free CORT, and stayed at the colony longer after reaching a morphological threshold. Our study suggests that as chicks lose mass, free CORT acts as a signal of energetic or nutritional state to adjust the timing of fledging.     

Crystal structure of the HSV-1 Fc receptor bound to Fc reveals a mechanism for antibody bipolar bridging

Herpes simplex virus type-1 expresses a heterodimeric Fc receptor, gE-gI, on the surfaces of virions and infected cells that binds the Fc region of host immunoglobulin G and is implicated in the cell-to-cell spread of virus. gE-gI binds immunoglobulin G at the basic pH of the cell surface and releases it at the acidic pH of lysosomes, consistent with a role in facilitating the degradation of antiviral antibodies. Here we identify the C-terminal domain of the gE ectodomain (CgE) as the minimal Fc-binding domain and present a 1.78-Å CgE structure. A 5-Å gE-gI/Fc crystal structure, which was independently verified by a theoretical prediction method, reveals that CgE binds Fc at the C _H2-C _H3 interface, the binding site for several mammalian and bacterial Fc-binding proteins. The structure identifies interface histidines that may confer pH-dependent binding and regions of CgE implicated in cell-to-cell spread of virus. The ternary organization of the gE-gI/Fc complex is compatible with antibody bipolar bridging, which can interfere with the antiviral immune response.     

Structural and functional consequences of galactolipids on thylakoid membrane organization

Photosynthetic membranes of higher plant chloroplasts are composed primarily of polar, but uncharged, galactolipids unlike most mammalian membranes which contain large amounts of phosphatidylcholine. It is unclear what role(s) the galactolipids play in maintaining the differentiated thylakoid membranes, or in stabilizing the photosynthetically active enzyme complexes. Some of the membrane complexes show no lipid selectivity for maintaining structural or functional integrity. Others are poisoned or dissociated in the presence of high concentrations of a trace lipid class. The efficiency of energy transfer and the reconstitution of protein complexes into liposomes are dependent on the lipid class employed. The lipids are asymmetrically arranged along and across the thylakoid membranes but not as distinctly as the proteins.Abbreviations DGDG digalactosyldiglyceride - MGDG monogalactosyldiglyceride - SQDG sulfoquinovosyldiglyceride - PG phosphatidylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PSI photosystem I - PSII photosystem II - LHC chlorophylla/b lightharvesting complex - cytb ₆ f cytochromeb ₆ f complex - CF₀/CF₁ coupling factor ATPase - DCIP 2,6-dichlorophenolindophenol - LRa galactolipase fromRhizopus arrhis     

pH dependence and stoichiometry of binding to the Fc region of IgG by the herpes simplex virus Fc receptor gE-gI

Herpes simplex virus type 1 encodes two glycoproteins, gE and gI, that form a heterodimer on the surface of virions and infected cells. The gE-gI heterodimer has been implicated in cell-to-cell spread of virus and is a receptor for the Fc fragment of IgG. Previous studies localized the gE-gI-binding site on human IgG to a region near the interface between the C(H)2 and C(H)3 domains of Fc, which also serves as the binding site for bacterial and mammalian Fc receptors. Although there are two potential gE-gI-binding sites per Fc homodimer, only one gE-gI heterodimer binds per IgG in gel filtration experiments. Here we report production of recombinant human Fc molecules that contain zero, one, or two potential gE-gI-binding sites and use them in analytical ultracentrifugation experiments to show that two gE-gI heterodimers can bind to each Fc. Further characterization of the gE-gI interaction with Fc reveals a sharp pH dependence of binding, with K(D) values of approximately 340 and approximately 930 nm for the first and second binding events, respectively, at the slightly basic pH of the cell surface (pH 7.4), but undetectable binding at pH 6.0. This strongly pH-dependent interaction suggests a physiological role for gE-gI dissociation from IgG within acidic intracellular compartments, consistent with a mechanism whereby herpes simplex virus promotes intracellular degradation of anti-viral antibodies.     

Urmylation: a ubiquitin-like pathway that functions during invasive growth and budding in yeast

Ubiquitin is a small modifier protein that is conjugated to substrates to target them for degradation. Recently, a surprising number of ubiquitin-like proteins have been identified that also can be attached to proteins. Herein, we identify two molecular functions for the posttranslational protein modifier from Saccharomyces cerevisiae, Urm1p. Simultaneous loss of Urm1p and Cla4p, a p21-activated kinase that functions in budding, is lethal. This result suggests a role for the urmylation pathway in budding. Furthermore, loss of the urmylation pathway causes defects in invasive growth and confers sensitivity to rapamycin. Our results indicate that the sensitivity to rapamycin is due to a genetic interaction with the TOR pathway, which is important for regulation of cell growth in response to nutrients. We have found that Urm1p can be attached to a number of proteins. Loss of five genes that are also essential in a cla4Delta strain, NCS2, NCS6, ELP2, ELP6, and URE2, affect the level of at least one Urm1p conjugate. Moreover, these five genes have a role in invasive growth and display genetic interactions with the TOR pathway. In summary, our results suggest the urmylation pathway is involved in nutrient sensing and budding.     

Intertroop Transfer and Dominance Rank Structure of Nonnatal Male Japanese Macaques in Yakushima, Japan

We examined the interaction between intertroop transfer and male dominance ranks in a wild population of Japanese macaques (Macaca fuscata yakui) in Yakushima using data collected over 15 years. Intertroop transfer tended to maintain a linear, stable, and age-graded dominance rank order among nonnatal males irrespective of variation in troop size or composition. All males that joined a troop at the top of the rank order were prime adults. Among males joining at lower ranks, entry at the most subordinate position in the hierarchy was common. Males joining at lower ranks tended to join troops in which all other resident males were the same age or older. Adult males tended to join troops with few or no males. Young males tended to join troops with many resident males, and in which a relatively large proportion of males was other young ones. Intertroop transfer was responsible for most rank changes of resident males. The most common cause of males rising in rank was the emigration or death of a higher-ranking male. Males fell in rank most frequently as a result of a new male joining the troop at the top of the hierarchy. Rank reversals among resident males were rare. The cumulative effects of male transfers produce sociodemographic variation within a troop over time and sociodemographic diversity among troops in a local population. A key feature of intertroop diversity is that larger troops have a significantly greater proportion of young males than smaller troops. This diversity also creates the potential for intertroop variation in the severity of male competition and provides a range of options for transferring males.