The ribosome-associated complex antagonizes prion formation in yeast

The number of known fungal proteins capable of switching between alternative stable conformations is steadily increasing, suggesting that a prion-like mechanism may be broadly utilized as a means to propagate altered cellular states. To gain insight into the mechanisms by which cells regulate prion formation and toxicity we examined the role of the yeast ribosome-associated complex (RAC) in modulating both the formation of the [PSI⁺] prion – an alternative conformer of Sup35 protein – and the toxicity of aggregation-prone polypeptides. The Hsp40 RAC chaperone Zuo1 anchors the RAC to ribosomes and stimulates the ATPase activity of the Hsp70 chaperone Ssb. We found that cells lacking Zuo1 are sensitive to over-expression of some aggregation-prone proteins, including the Sup35 prion domain, suggesting that co-translational protein misfolding increases in Δzuo1 strains. Consistent with this finding, Δzuo1 cells exhibit higher frequencies of spontaneous and induced prion formation. Cells expressing mutant forms of Zuo1 lacking either a C-terminal charged region required for ribosome association, or the J-domain responsible for Ssb ATPase stimulation, exhibit similarly high frequencies of prion formation. Our findings are consistent with a role for the RAC in chaperoning nascent Sup35 to regulate folding of the N-terminal prion domain as it emerges from the ribosome.     

ERRATUM: Effects of Loading on the Biomechanical Behavior of Molars of Homo,Pan, and Pongo. Am J Phys Anthropol 109:211–227.

ERRATUM: Macho GA and Spears IR. 1999. Effects of Loading on the Biomechanical Behavior of Molars of Homo, Pan, and Pongo. Am J Phys Anthropol 109:211–227. The correct title of the article is given above. The word “biochemical” should be read as “biomechanical.”     

Deconvolution of intergenic polymorphisms determining high expression of Factor H binding protein in meningococcus and their association with invasive disease

Neisseria meningitidis is a strictly human pathogen and is the major cause of septicemia and meningitis worldwide. Factor H binding protein (fHbp) is a meningococcal surface-exposed lipoprotein that binds the human Complement factor H allowing the bacterium to evade the host innate immune response. FHbp is also a key antigen in two vaccines against N. meningitidis serogroup B. Although the fHbp gene is present in most circulating meningococcal strains, level of fHbp expression varies among isolates and has been correlated to differences in promoter sequences upstream of the gene. Here we elucidated the sequence determinants that control fHbp expression in globally circulating strains. We analyzed the upstream fHbp intergenic region (fIR) of more than 5800 strains representative of the UK circulating isolates and we identified eleven fIR sequence alleles which represent 88% of meningococcal strains. By engineering isogenic recombinant strains where fHbp expression was under the control of each of the eleven fIR alleles, we confirmed that the fIR sequence determines a specific and distinct level of expression. Moreover, we identified the molecular basis for variation in expression through polymorphisms within key regulatory regions that are known to affect fHbp expression. We experimentally established three expression groups, high–medium–low, that correlated directly with the susceptibility to killing mediated by anti-fHbp antibodies and the ability of the meningococcal strain to survive within human serum. By using this sequence classification and information about the variant, we predicted fHbp expression in the panel of UK strains and we observed that strains with higher expressing fIR alleles are more likely associated with invasive disease. Overall, our findings can contribute to understand and predict vaccine coverage mediated by fHbp as well as to shed light on the role of this virulence factor in determining an invasive phenotype.     

Spatial Distribution and Fruiting Phenology of Protium heptaphyllum (Burseraceae) Determine the Design of the Underground Foraging System of Atta sexdens L. (Hymenoptera: Formicidae)

Leaf-cutting ants have long been recognized to forage via complex trail systems but the nature and the ecological drivers of the different foraging strategies adopted remain a key topic. Here, we described the spatiotemporal use of belowground foraging galleries by Atta sexdens L. in the Brazilian Atlantic forest, and examined the adaptive advantages of this foraging strategy. Protium heptaphyllum adult trees (DBH?>?10?cm), seed/seedling clumps and ant gallery entrances were mapped across two 1-ha plots during two consecutive fruiting seasons (2002 and 2004). We recorded 75 ca. 40?cm deep gallery entrances beneath 26 P. heptaphyllum trees at nest distances ranging from 14 to 57?m. Furthermore, gallery abundance and galleries associated with seed/seedling clumps correlated positively with P. heptaphyllum density. Our results indicate that A. sexdens was able to set a permanent system of underground galleries targeting P. heptaphyllum trees and their seeds on the ground. Such network of galleries was spatially arranged according to both the spatial distribution and abundance of P. heptaphyllum trees in a way that most gallery entrances were disposed beneath or in close periphery of P. heptaphyllum crowns. Our findings suggest that underground trail systems shaped by fruit resources represent a foraging strategy clearly more common than existing literature on the subject would suggest. In addition, it reinforces the notion that the spatiotemporal availability of resources combined with predation risk largely influence trail configurations as well as overall foraging strategies adopted by leaf-cutting ants.     

Metapopulation structure,population trends,and status of Florida Grasshopper Sparrows

ABSTRACT The federally Endangered Florida Grasshopper Sparrow (FGSP, Ammodramus savannarum floridanus) is endemic to dry prairie habitat in central Florida and is currently only found at three public management areas (Avon Park Air Force Range, APAFR; Kissimmee Prairie Preserve State Park, KPPSP; and Three Lakes Wildlife Management Area, TLWMA). We analyzed long‐term (1991–2008) point‐count data to compare population trends of FGSPs at these management areas to determine if they function as independent populations by using Spearman's rank correlation to test for independence between annual trends. We also examined banding and resighting data to infer metapopulation structure. Populations fluctuated across years at all three sites, declining significantly at APAFR (r_s=?0.89, P < 0.001, N= 13) and KPPSP (r_s=?0.78, P= 0.004, N= 11) and remaining stable at TLWMA (r_s= 0.19, P= 0.46, N= 17). Population trends among the three management areas appeared independent (absolute value of r_s≤ 0.50, P≥ 0.12). Previous studies indicated that sparrows in the three areas were not genetically differentiated, and two cases of dispersal between APAFR and KPPSP have been documented. However, dispersal rates among areas appear to be too low to influence demographic dynamics within individual areas. Within APAFR, FGSPs are aggregated into three spatially distinct habitat patches previously considered separate populations, but dispersal among these patches is more frequent than previously reported and population trends among these patches are correlated (r_s≥ 0.91, P < 0.001). These patterns suggest that a single metapopulation of FGSPs exists consisting of three distinct populations (APAFR, KPPSP, and TLWMA), and the spatially distinct aggregations at APAFR constitute a single population using several habitat patches. The population at APAFR is at risk of extirpation, and immediate action is needed if that population is to recover. Taking broader metapopulation dynamics into account will be useful for guiding management efforts aimed at conserving the FGSP in the broader central Florida landscape.     

High-grade transgenic somatic chimeras from chicken embryonic stem cells

Male and female embryonic stem (ES) cell lines were derived from the area pellucidae of Stage X (EG&K) chicken embryos. These ES cell lines were grown in culture for extended periods of time and the majority of the cells retained a diploid karyotype. When reintroduced into Stage VI-X (EG&K) recipient embryos, the cES cells were able to contribute to all somatic tissues. By combining irradiation of the recipient embryo with exposure of the cES cells to the embryonic environment in diapause, a high frequency and extent of chimerism was obtained. High-grade chimeras, indistinguishable from the donor phenotype by feather pigmentation, were produced. A transgene encoding GFP was incorporated into the genome of cES cells under control of the ubiquitous promoter CX and GFP was widely expressed in somatic tissues. Although cES cells made extensive contributions to the somatic tissues, contribution to the germline was not observed.     

Chromosomal mapping and candidate gene discovery of chicken developmental mutants and genome-wide variation analysis of MHC congenics

The chicken has been widely used in experimental research given its importance to agriculture and its utility as a model for vertebrate biology and biomedical pursuits for over 100 years. Herein we used advanced technologies to investigate the genomic characteristics of specialized chicken congenic genetic resources developed on a highly inbred background. An Illumina 3K chicken single nucleotide polymorphism (SNP) array was utilized to study variation within and among major histocompatibility complex (MHC)-congenic lines as well as investigate line-specific genomic diversity, inbreeding coefficients, and MHC B haplotype-specific GGA 16 SNP profiles. We also investigated developmental mutant-congenic lines to map a number of single-gene mutations using both the Illumina 3K array and a recently developed Illumina 60K chicken SNP array. In addition to identifying the chromosomes and specific subregions, the mapping results affirmed prior analyses indicating recessive or dominant and autosomal or sex chromosome modes of inheritance. Priority candidate genes are described for each mutation based on association with similar phenotypes in other vertebrates. These single-gene mutations provide a means of studying amniote development and in particular serve as invaluable biomedical models for similar malformations found in human.     

Metal ion-assembled micro-collagen heterotrimers

Collagen mimetic peptides (CMPs) provide critical insight into the assembly, stability, and structure of the triple helical collagen protein. The majority of natural fibrous collagens are aab or abc heterotrimers, yet few examples of heterotrimeric CMPs have been reported. Previously, CMP heterotrimers have only been accessible by total syntheses or by introducing complementary interstrand electrostatic or steric interactions. Here, we describe an abc CMP heterotrimer in which each contributing CMP consists of only three amino acids: glycine, proline and 4-hydroxyproline. Assembly of the heterotrimeric triple helix is directed by a combination of metal-ion coordination to set the relative register of the CMPs, and minimization of valence frustration to direct heterotrimerization. Assembly of the four-component mixture is facile and extremely rapid, and equilibration to the abc heterotrimer occurs within a few hours at modestly elevated temperatures. The melting temperatures of the metal-assembled collagen trimers are higher by some 30°C than the apopeptide assemblies. Two iterations of the design are described, and the outcomes suggest possibilities for designing self-assembling abc and abb heterotrimers.