Acorn mast drives long-term dynamics of rodent and songbird populations

Resource pulses can have cascading effects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in oak-dominated forests that has significant direct effects on acorn predators and indirect effects on their predators, prey, and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success of a ground-nesting songbird over a 24-year period (1980–2004) in the southern Appalachian Mountains in an effort to determine the relationships among the four trophic levels. In particular, we examined the following: acorn mast from red oaks (Quercus rubra) and white oaks (Q. alba), abundance of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus), population estimates of seven raptor species from three feeding guilds, and nest failure and number of juveniles of dark-eyed juncos (Junco hyemalis). Finally, we recorded seasonal temperature and precipitation to determine the effects of weather on each trophic level. We found that weather patterns had delayed effects of up to 3 years on these trophic interactions. Variation in acorn mast, the keystone resource in this community, was explained by weather conditions as far back as 2 years before the mast event. Acorn mast, in turn, was a strongly positive predictor of rodent abundance the following year, whereas spring and summer temperature and raptor abundance negatively affected rodent abundance. Dark-eyed junco nests were more likely to fail in years in which there were more rodents and raptors. Nest failure rate was a strong predictor of the number of juvenile juncos caught at the end of the summer. Our results improve our understanding of the complex ecological interactions in oak-dominated forests by illustrating the importance of abiotic and biotic factors at different trophic levels. Ethan D. Clotfelter and Amy B. Pedersen contributed equally to the writing of this paper.     

Interspecies chimera between primate embryonic stem cells and mouse embryos: monkey ESCs engraft into mouse embryos, but not post-implantation fetuses

Unequivocal evidence for pluripotency in which embryonic stem cells contribute to chimeric offspring has yet to be demonstrated in human or nonhuman primates (NHPs). Here, rhesus and baboons ESCs were investigated in interspecific mouse chimera generated by aggregation or blastocyst injection. Aggregation chimera produced mouse blastocysts with GFP-nhpESCs at the inner cell mass (ICM), and embryo transfers (ETs) generated dimly-fluorescencing abnormal fetuses. Direct injection of GFP-nhpESCs into blastocysts produced normal non-GFP-fluorescencing fetuses. Injected chimera showed >70% loss of GFP-nhpESCs after 21 h culture. Outgrowths of all chimeric blastocysts established distinct but separate mouse- and NHP-ESC colonies. Extensive endogenous autofluorescence compromised anti-GFP detection and PCR analysis did not detect nhpESCs in fetuses. NhpESCs localize to the ICM in chimera and generate pregnancies. Because primate ESCs do not engraft post-implantation, and also because endogenous autofluorescence results in misleading positive signals, interspecific chimera assays for pluripotency with primate stem cells is unreliable with the currently available ESCs. Testing primate ESCs reprogrammed into even more na?ve states in these inter-specific chimera assays will be an important future endeavor.     

Structural comparison of MTA phosphorylase and MTA/AdoHcy nucleosidase explains substrate preferences and identifies regions exploitable for inhibitor design

The development of new and effective antiprotozoal drugs has been a difficult challenge because of the close similarity of the metabolic pathways between microbial and mammalian systems. 5'-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) nucleosidase is thought to be an ideal target for therapeutic drug design as the enzyme is present in many microbes but not in mammals. MTA/AdoHcy nucleosidase (MTAN) irreversibly depurinates MTA or AdoHcy to form adenine and the corresponding thioribose. The inhibition of MTAN leads to a buildup of toxic byproducts that affect various microbial pathways such as quorum sensing, biological methylation, polyamine biosynthesis, and methionine recycling. The design of nucleosidase-specific inhibitors is complicated by its structural similarity to the human MTA phosphorylase (MTAP). The crystal structures of human MTAP complexed with formycin A and 5'-methylthiotubercidin have been solved to 2.0 and 2.1 A resolution, respectively. Comparisons of the MTAP and MTAN inhibitor complexes reveal size and electrostatic potential differences in the purine, ribose, and 5'-alkylthio binding sites, which account for the substrate specificity and reactions catalyzed. In addition, the differences between the two enzymes have allowed the identification of exploitable regions that can be targeted for the development of high-affinity nucleosidase-specific inhibitors. Sequence alignments of Escherichia coli MTAN, human MTAP, and plant MTA nucleosidases also reveal potential structural changes to the 5'-alkylthio binding site that account for the substrate preference of plant MTA nucleosidases.     

The Influence of Exogenous Testosterone on the Dynamics of Nestling Provisioning in Dark-Eyed Juncos

In many songbird species, application of exogenous testosterone (T) during the breeding season has the general effects of reducing male parental investment and increasing allocation of time and energy to mating. Most studies record the number of feeding trips made by males as a function of their hormone treatment, but few have investigated the ways in which testosterone affects the dynamics of male and female provisioning behavior or the quantity of food delivered by males. We attempt to fill these gaps in our understanding of testosterone and male parental effort by utilizing data from a long‐term study on the behavioral endocrinology of the dark‐eyed junco (Junco hyemalis). We found that male and female feeding rates covaried positively, although to different degrees, throughout the nestling period, but that this relationship was degraded in pairs in which males were given T implants. We also found that the coefficients of variation in the duration of intervals between successive feeding trips by males and females were highly positively related in broods of older nestlings. Male hormone treatment, however, had no effect on the coefficients of variation in either male or female feeding intervals. Finally, we examined the quantity of prey delivered by males and found no significant effect of hormone treatment.     

MiR-449a Affects Epithelial Proliferation during the Pseudoglandular and Canalicular Phases of Avian and Mammal Lung Development

Congenital diaphragmatic hernia is associated with pulmonary hypoplasia and respiratory distress, which result in high mortality and morbidity. Although several transgenic mouse models of lung hypoplasia exist, the role of miRNAs in this phenotype is incompletely characterized. In this study, we assessed microRNA expression levels during the pseudoglandular to canalicular phase transition of normal human fetal lung development. At this critical time, when the distal respiratory portion of the airways begins to form, microarray analysis showed that the most significantly differentially expressed miRNA was miR-449a. Prediction algorithms determined that N-myc is a target of miR-449a and identified the likely miR-449a:N-myc binding sites, confirmed by luciferase assays and targeted mutagenesis. Functional ex vivo knock-down in organ cultures of murine embryonic lungs, as well as in ovo overexpression in avian embryonic lungs, suggested a role for miR-449a in distal epithelial proliferation. Finally, miR-449a expression was found to be abnormal in rare pulmonary specimens of human fetuses with Congenital Diaphragmatic Hernia in the pseudoglandular or canalicular phase. This study confirms the conserved role of miR-449a for proper pulmonary organogenesis, supporting the delicate balance between expansion of progenitor cells and their terminal differentiation, and proposes the potential involvement of this miRNA in human pulmonary hypoplasia.     

Integration of biological networks and gene expression data using Cytoscape

Cytoscape is a free software package for visualizing, modeling and analyzing molecular and genetic interaction networks. This protocol explains how to use Cytoscape to analyze the results of mRNA expression profiling, and other functional genomics and proteomics experiments, in the context of an interaction network obtained for genes of interest. Five major steps are described: (i) obtaining a gene or protein network, (ii) displaying the network using layout algorithms, (iii) integrating with gene expression and other functional attributes, (iv) identifying putative complexes and functional modules and (v) identifying enriched Gene Ontology annotations in the network. These steps provide a broad sample of the types of analyses performed by Cytoscape.