Persistent maternal effects on juvenile survival in North American red squirrels

Maternal effects can have lasting fitness consequences for offspring, but these effects are often difficult to disentangle from associated responses in offspring traits. We studied persistent maternal effects on offspring survival in North American red squirrels (Tamiasciurus hudsonicus) by manipulating maternal nutrition without altering the post-emergent nutritional environment experienced by offspring. This was accomplished by providing supplemental food to reproductive females over winter and during reproduction, but removing the supplemental food from the system prior to juvenile emergence. We then monitored juvenile dispersal, settlement and survival from birth to 1 year of age. Juveniles from supplemented mothers experienced persistent and magnifying survival advantages over juveniles from control mothers long after supplemental food was removed. These maternal effects on survival persisted, despite no observable effect on traits normally associated with high offspring quality, such as body size, dispersal distance or territory quality. However, supplemented mothers did provide their juveniles an early start by breeding an average of 18 days earlier than control mothers, which may explain the persistent survival advantages their juveniles experienced.     

Prion Propagation: The Role of Protein Dynamics

The transfer of phenotypes from one individual to another is a fundamental aspect of biology. In addition to traditional nucleic acid-based genetic determinants, unique proteins known as prions can also act as elements of inheritance, infectivity, and disease. Nucleic acids and proteins encode genetic information in distinct ways, either in the sequence of bases in DNA or RNA or in the three dimensional structure of the polypeptide chain. Given these differences in the nature of the genetic repository, the mechanisms underlying the transmission of nucleic acid-based and protein-based phenotypes are necessarily distinct. While the appearance, persistence and transfer of nucleic acid determinants require the synthesis of new polymers, recent studies indicate that prions are propagated through dynamic transitions in the structure of existing protein.Key Words: prion, PrP, [PSI⁺], [URE3], [Het-s], Sup35, Ure2, Het-s, Hsp104     

The pathogenic fungus Cryptococcus neoformans expresses two functional GDP-mannose transporters with distinct expression patterns and roles in capsule synthesis

Cryptococcus neoformans is a fungal pathogen that is responsible for life-threatening disease, particularly in the context of compromised immunity. This organism makes extensive use of mannose in constructing its cell wall, glycoproteins, and glycolipids. Mannose also comprises up to two-thirds of the main cryptococcal virulence factor, a polysaccharide capsule that surrounds the cell. The glycosyltransfer reactions that generate cellular carbohydrate structures usually require activated donors such as nucleotide sugars. GDP-mannose, the mannose donor, is produced in the cytosol by the sequential actions of phosphomannose isomerase, phosphomannomutase, and GDP-mannose pyrophosphorylase. However, most mannose-containing glycoconjugates are synthesized within intracellular organelles. This topological separation necessitates a specific transport mechanism to move this key precursor across biological membranes to the appropriate site for biosynthetic reactions. We have discovered two GDP-mannose transporters in C. neoformans, in contrast to the single such protein reported previously for other fungi. Biochemical studies of each protein expressed in Saccharomyces cerevisiae show that both are functional, with similar kinetics and substrate specificities. Microarray experiments indicate that the two proteins Gmt1 and Gmt2 are transcribed with distinct patterns of expression in response to variations in growth conditions. Additionally, deletion of the GMT1 gene yields cells with small capsules and a defect in capsule induction, while deletion of GMT2 does not alter the capsule. We suggest that C. neoformans produces two GDP-mannose transporters to satisfy its enormous need for mannose utilization in glycan synthesis. Furthermore, we propose that the two proteins have distinct biological roles. This is supported by the different expression patterns of GMT1 and GMT2 in response to environmental stimuli and the dissimilar phenotypes that result when each gene is deleted.     

Hsp104-dependent remodeling of prion complexes mediates protein-only inheritance

Inheritance of phenotypic traits depends on two key events: replication of the determinant of that trait and partitioning of these copies between mother and daughter cells. Although these processes are well understood for nucleic acid–based genes, the mechanisms by which protein-only or prion-based genetic elements direct phenotypic inheritance are poorly understood. Here, we report a process crucial for inheritance of the Saccharomyces cerevisiae prion [PSI⁺], a self-replicating conformer of the Sup35 protein. By tightly controlling expression of a Sup35-GFP fusion, we directly observe remodeling of existing Sup35^[PSI+] complexes in vivo. This dynamic change in Sup35^[PSI+] is lost when the molecular chaperone Hsp104, a factor essential for propagation of all yeast prions, is functionally impaired. The loss of Sup35^[PSI+] remodeling by Hsp104 decreases the mobility of these complexes in the cytosol, creates a segregation bias that limits their transmission to daughter cells, and consequently diminishes the efficiency of conversion of newly made Sup35 to the prion form. Our observations resolve several seemingly conflicting reports on the mechanism of Hsp104 action and point to a single Hsp104-dependent event in prion propagation.     

Classifying behavior from short‐interval biologging data: An example with GPS tracking of birds

1. Recent advances in digital data collection have spurred accumulation of immense quantities of data that have potential to lead to remarkable ecological insight, but that also present analytic challenges. In the case of biologging data from birds, common analytical approaches to classifying movement behaviors are largely inappropriate for these massive data sets.
2. We apply a framework for using K‐means clustering to classify bird behavior using points from short time interval GPS tracks. K‐means clustering is a well‐known and computationally efficient statistical tool that has been used in animal movement studies primarily for clustering segments of consecutive points. To illustrate the utility of our approach, we apply K‐means clustering to six focal variables derived from GPS data collected at 1–11 s intervals from free‐flying bald eagles (Haliaeetus leucocephalus) throughout the state of Iowa, USA. We illustrate how these data can be used to identify behaviors and life‐stage‐ and age‐related variation in behavior.
3. After filtering for data quality, the K‐means algorithm identified four clusters in >2 million GPS telemetry data points. These four clusters corresponded to three movement states: ascending, flapping, and gliding flight; and one non‐moving state: perching. Mapping these states illustrated how they corresponded tightly to expectations derived from natural history observations; for example, long periods of ascending flight were often followed by long gliding descents, birds alternated between flapping and gliding flight.
4. The K‐means clustering approach we applied is both an efficient and effective mechanism to classify and interpret short‐interval biologging data to understand movement behaviors. Furthermore, because it can apply to an abundance of very short, irregular, and high‐dimensional movement data, it provides insight into small‐scale variation in behavior that would not be possible with many other analytical approaches.

     

Ciliary neurotrophic factor upregulates ubiquitin-proteasome components in a rat model of neuronal injury

Neuronal injury triggers the release of ciliary neurotrophic factor (CNTF), promoting local neuronal repair but producing systemic effects of anorexia and lean body weight loss. Due to the rapid rate of systemic protein loss stimulated by CNTF, we hypothesized involvement of the hepatic ubiquitin-proteasome proteolytic (UPP) pathway in CNTF-induced proteolysis. To assess the role of central CNTF in systemic UPP regulation, we measured hepatic UPP mRNA and proteasome activity in a rat model of neuronal injury and determined alterations induced by intracerebroventricular (ICV) administration of CNTF-neutralizing antibody or additional exogenous CNTF. We also assessed proteolytic parameters and nutritional status by measuring caloric intake, body weight, and protein levels. We produced neuronal injury by implanting a lateral ventricle cannula and giving daily ICV saline bolus injections, which increased hepatic 20S proteasome mRNA and enzymatic activity while reducing caloric intake, body weight, and protein levels compared to controls. Administration of ICV anti-CNTF antibodies (but not control antibodies) prevented these effects. Addition of exogenous CNTF augmented the weight loss along with the increases in 20S proteasome mRNA and proteolytic activity induced by neuronal injury. We conclude that CNTF decreases lean body weight through a combination of appetite inhibition and UPP pathway activation.     

Ghrelin can bind to a species of high density lipoprotein associated with paraoxonase

Ghrelin is a 28-residue peptide hormone that is principally released from the stomach during fasting and prior to eating. Two forms are present in human plasma: the unmodified peptide and a less abundant acylated version, in which octanoic acid is attached to the third residue, a serine, via an ester linkage. The acylated form of ghrelin acts as a ligand for the growth hormone secretagogue receptor and can stimulate the release of growth hormone from the pituitary gland. It also initiates behavioral and metabolic adaptations to fasting. Here we show that an immobilized form of ghrelin specifically binds a species of high density lipoprotein associated with the plasma esterase, paraoxonase, and clusterin. Both free ghrelin and paraoxon, a substrate for paraoxonase, can inhibit this interaction. An endogenous species of ghrelin is found to co-purify with high density lipoprotein during density gradient centrifugation and subsequent gel filtration. This interaction links the orexigenic peptide hormone ghrelin to lipid transport and metabolism. Furthermore, the interaction of the esterified hormone ghrelin with a species of HDL containing an esterase suggests a possible mechanism for the conversion of ghrelin to des-acyl ghrelin.