Under‐representation of avian studies in landscape genetics

Landscape genetics is a rapidly growing discipline that examines how heterogeneous landscapes and other environmental factors influence population genetic variation. We conducted a systematic review of the landscape genetic literature which demonstrates that birds are severely under‐represented relative to their species diversity and general publication prevalence. Most avian studies were on species that have relatively low dispersal ability, and we suggest that this reflects an assumed high vagility of birds that precludes spatial genetic variation relatable to landscape heterogeneity. However, spatial genetic variation exists in several bird species with very high dispersal ability, but this has not been considered in the context of landscape features. Genetic patterns may also relate to landscape due to breeding habitat selection and territorial behaviour, despite the fact that species may be able to move throughout different landscape elements with minimal movement costs. Habitat loss and fragmentation are continuing globally and are strongly related to declines in bird populations. Landscape genetic studies provide a means to understand, predict and mitigate the effects of anthropogenic landscape change on birds. This review promotes the need for landscape genetic studies of birds, such that a greater understanding of the drivers of their genetic structuring can be developed and generalizations can be made from landscape genetic studies that apply more broadly across taxa.     

Terminal Regions Confer Plasticity to the Tetrameric Assembly of Human HspB2 and HspB3

Heterogeneity in small heat shock proteins (sHsps) spans multiple spatiotemporal regimes—from fast fluctuations of part of the protein, to conformational variability of tertiary structure, plasticity of the interfaces, and polydispersity of the inter-converting, and co-assembling oligomers. This heterogeneity and dynamic nature of sHsps has significantly hindered their structural characterization. Atomic coordinates are particularly lacking for vertebrate sHsps, where most available structures are of extensively truncated homomers. sHsps play important roles in maintaining protein levels in the cell and therefore in organismal health and disease. HspB2 and HspB3 are vertebrate sHsps that are found co-assembled in neuromuscular cells, and variants thereof are associated with disease. Here, we present the structure of human HspB2/B3, which crystallized as a hetero-tetramer in a 3:1 ratio. In the HspB2/B3 tetramer, the four α-crystallin domains (ACDs) assemble into a flattened tetrahedron which is pierced by two non-intersecting approximate dyads. Assembly is mediated by flexible “nuts and bolts” involving IXI/V motifs from terminal regions filling ACD pockets. Parts of the N-terminal region bind in an unfolded conformation into the anti-parallel shared ACD dimer grooves. Tracts of the terminal regions are not resolved, most likely due to their disorder in the crystal lattice. This first structure of a full-length human sHsp heteromer reveals the heterogeneous interactions of the terminal regions and suggests a plasticity that is important for the cytoprotective functions of sHsps.     

HuR binds to a single site on the C/EBPbeta mRNA of 3T3-L1 adipocytes

HuR is a ligand for nuclear mRNAs containing adenylate-uridylate rich elements in the 3'-untranslated region. Once bound to the mRNA, HuR is recognized by adapter proteins which then facilitate nuclear export of the complex. In the cytosol HuR is thought to function to control stability and translation of its ligand message. In the 3T3-L1 cells HuR is constitutively expressed and localized predominantly to the nucleus in the preadipocytes. However within 30 min of exposure to the differentiation stimulus, the HuR content in the cytosol increases consistent with HuR regulating the availability of relevant mRNAs for translation. Using in vitro RNA gel shifts, we have demonstrated that the C/EBPbeta message is a ligand for HuR and that the single binding site is an adenylate-uridylate rich element in the 3'-untranslated region.     

Probing the disulfide folding pathway of insulin‐like growth factor‐I

The crucial step of folding of recombinant proteins presents serious challenges to obtaining the native structure. This problem is exemplified by insulin‐like growth factor (IGF)‐I which when refolded in vitro produces the native three‐disulfide structure, an alternative structure with mispaired disulfide bonds and other isomeric forms. To investigate this phenomenon we have examined the refolding properties of an analog of IGF‐I which contains a 13‐amino acid N‐terminal extension and a charge mutation at position 3 (Long‐ [Arg³]IGF‐I). Unlike IGF‐I, which yields 45% of the native structure and 24% of the alternative structure when refolded in vitro, Long‐[Arg³]GF‐I yields 85% and 10% of these respective forms. To investigate the interactions that affect the refolding of Long‐[Arg³]IGF‐I and IGF‐I, we acid‐trapped folding intermediates and products for inclusion in a kinetic analysis of refolding. In addition to non‐native intermediates, three native‐like intermediates were identified, that appear to have a major role in the in vitro refolding pathway of Long‐[Arg³]IGF‐I; a single‐disulfide Cys¹⁸–Cys⁶¹ intermediate, an intermediate with Cys¹⁸–Cys⁶¹ and Cys⁶–Cys⁴⁸ disulfide bonds and another with Cys¹⁸–Cys⁶¹ and Cys⁴⁷–Cys⁵² disulfide bonds. Furthermore, from our kinetic analysis we propose that the Cys¹⁸‐Cys⁶¹, Cys⁶‐Cys⁴⁸ intermediate forms the native structure, not by the direct formation of the last (Cys⁴⁷‐Cys⁵²) disulfide bond, but by rearrangement via the Cys¹⁸–Cys⁶¹ intermediate and a productive Cys¹⁸–Cys⁶¹, Cys⁴⁷–Cys⁵² intermediate. In this pathway, the last disulfide bond to form involves Cys⁶ and Cys⁴⁸. Finally, we apply this pathway to IGF‐I and conclude that the divergence in the in vitro folding pathway of IGF‐I is caused by non‐native interactions involving Glu³ that stabilize the alternative structure. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 693–703, 1999.     

Intrinsic factors drive spatial genetic variation in a highly vagile species,the wedge‐tailed eagle Aquila audax,in Tasmania

Knowledge of dispersal in a species, both its quantity and the factors influencing it, are crucial for our understanding of ecology and evolution, and for species conservation. Here we quantified and formally assessed the potential contribution of extrinsic factors on individual dispersal in the threatened Tasmanian population of wedge‐tailed eagle Aquila audax. As successful breeding by these individuals appears strongly related to habitat, we tested the effect of landscape around sampling sites on genetic diversity and spatial genetic variation, as these are influenced by patterns of dispersal. Similarly, we also tested whether habitat intervening sampling sites could explain spatial genetic variation. Twenty microsatellites were scored, but only a small proportion of spatial genetic variation (4.6%) could be explained by extrinsic factors, namely habitat suitability and elevation between sites. However, significant clinal genetic variation was evident across Tasmania, which we explain by intrinsic factors, likely high natal philopatry and occasional long‐distance dispersal. This study demonstrates that spatial genetic variation can be detected in highly vagile species at spatial scales that are small relative to putative dispersal ability, although here there was no substantial relationship with landscape factors tested.