The initial stages of oogenesis and their relation to differential fertility in the honey bee (Apis mellifera) castes

Neither the overall differences in ovariole number nor the caste-specifically modulated expression of vitellogenin can fully explain the striking caste differences in honey bee reproduction, in particular the mechanisms that block oogenesis in virgin queens and in workers kept in the presence of a queen. For this reason we investigated the initial stages of oogenesis in queens in relation to mating status and in workers exposed to different social conditions. A striking feature in ovarioles of both castes was a considerably elongated terminal filament which consisted not only of normal terminal filament cells but also contained apparently undifferentiated cells that were tentatively considered as stem cells. BrdU incorporation was detected in the upper germarium, as well as in the terminal filament. Cytoskeleton analysis by TRITC-phalloidin labeling for F-actin, and immunofluorescence detection for β-tubulin did not reveal structural differences in the early oogenesis steps between queens and queenless workers. In contrast, queenright workers showed signs of a disorganized microtubule and microfilament system that could explain the histological evidence for progressive cell death observed in the germaria. In addition to cytoplasmic tubulin we also detected marked intranuclear foci indicating the presence of nuclear β_II-tubulin.     

Cryptic speciation on the high seas; global phylogenetics of the copepod family Eucalanidae

Few genetic data are currently available to assess patterns of population differentiation and speciation in planktonic taxa that inhabit the open ocean. A phylogenetic study of the oceanic copepod family Eucalanidae was undertaken to develop a model zooplankton taxon in which speciation events can be confidently identified. A global survey of 20 described species (526 individuals) sampled from 88 locations worldwide found high levels of cryptic diversity at the species level. Mitochondrial (16S rRNA, CO1) and nuclear (ITS2) DNA sequence data support 12 new genetic lineages as highly distinct from other populations with which they are currently considered conspecific. Out of these 12, at least four are new species. The circumglobal, boundary current species Rhincalanus nasutus was found to be a cryptic species complex, with genetic divergence between populations unrelated to geographic distance. 'Conspecific' populations of seven species exhibited varying levels of genetic differentiation between Atlantic and Pacific basins, suggesting that continental landmasses form barriers to dispersal for a subset of circumglobal species. A molecular phylogeny of the family based on both mitochondrial (16S rRNA) and nuclear (ITS2, 18S rRNA) gene loci supports monophyly of the family Eucalanidae, all four eucalanid genera and the 'pileatus' and 'subtenuis' species groups.     

Solution structure of Sco1: a thioredoxin-like protein Involved in cytochrome c oxidase assembly

Sco1, a protein required for the proper assembly of cytochrome c oxidase, has a soluble domain anchored to the cytoplasmic membrane through a single transmembrane segment. The solution structure of the soluble part of apoSco1 from Bacillus subtilis has been solved by NMR and the internal mobility characterized. Its fold places Sco1 in a distinct subgroup of the functionally unrelated thioredoxin proteins. In vitro Sco1 binds copper(I) through a CXXXCP motif and possibly His 135 and copper(II) in two different species, thus suggesting that copper(II) is adventitious more than physiological. The Sco1 structure represents the first structure of this class of proteins, present in a variety of eukaryotic and bacterial organisms, and elucidates a link between copper trafficking proteins and thioredoxins. The availability of the structure has allowed us to model the homologs Sco1 and Sco2 from S. cerevisiae and to discuss the physiological role of the Sco family.     

Protein aggregation and amyloid fibril formation by an SH3 domain probed by limited proteolysis

The SH3 domains are small protein modules of 60-85 amino acid residues that are found in many proteins involved in intracellular signal transduction. The SH3 domain of the p85alpha subunit of bovine phosphatidylinositol 3'-kinase (PI3-SH3) under acidic solution adopts a compact denatured state from which amyloid fibrils are readily formed. This aggregation process has been found to be modulated substantially by solution conditions. Here, we have analyzed the conformational features of the native and acid denatured states of PI3-SH3 by limited proteolysis experiments using proteinase K and pepsin, respectively. Moreover, we have analyzed the propensity of PI3-SH3 to be hydrolyzed by pepsin at different stages in the process of aggregation and amyloid formation at pH 1.2 and 2.0 and compared the sites of proteolysis under these conditions with the conformational features of both native and aggregated PI3-SH3. The results demonstrate that the denatured state of PI3-SH3 formed at low pH is relatively resistant to proteolysis, indicating that it is partially folded. The long loop connecting beta-strands b and c in the native protein is the region in this structure most susceptible to proteolysis. Remarkably, aggregates of PI3-SH3 that are formed initially from this denatured state in acid solution display enhanced susceptibility to proteolysis of the long loop, suggesting that the protein becomes more unfolded in the early stages of aggregation. By contrast, the more defined amyloid fibrils that are formed over longer periods of time are completely resistant to proteolysis. We suggest that the protein aggregates formed initially are relatively dynamic species that are able readily to reorganize their interactions to enable formation of very well ordered fibrillar structures. In addition, the disordered and non-native character of the polypeptide chains in the early aggregates could be important in determining the high cytotoxicity that has been revealed in previous studies of these species.     

Molecular features of the broadly neutralizing immunoglobulin G1 b12 required for recognition of human immunodeficiency virus type 1 gp120

IgG1 b12 is a broadly neutralizing antibody against human immunodeficiency virus type 1 (HIV-1). The epitope recognized by b12 overlaps the CD4 receptor-binding site (CD4bs) on gp120 and has been a target for vaccine design. Determination of the three-dimensional structure of immunoglobulin G1 (IgG1) b12 allowed modeling of the b12-gp120 interaction in which the protruding third complementarity-determining region (CDR) of the heavy chain (H3) was crucial for antibody binding. In the present study, extensive mutational analysis of the antigen-binding site of Fab b12 was carried out to investigate the validity of the model and to identify residues important for gp120 recognition and, by inference, key to the anti-HIV-1 activity of IgG1 b12. In all, 50 mutations were tested: 40 in H3, 4 each in H2 and L1, and 2 in L3. The results suggest that the interaction of gp120 with H3 of b12 is crucially dependent not only on a Trp residue at the apex of the H3 loop but also on a number of residues at the base of the loop. The arrangement of these residues, including aromatic side chains and side chains that hydrogen bond across the base of the loop, may rigidify H3 for penetration of the recessed CD4-binding cavity. The results further emphasize the importance to gp120 binding of a Tyr residue at the apex of the H2 loop that forms a second finger-like structure and a number of Arg residues in L1 that form a positively charged, shelf-like structure. In general, the data are consistent with the b12-gp120 interaction model previously proposed. At the gene level, somatic mutation is seen to be crucial for the generation of many of the structural features described. The Fab b12 mutants were also tested against the b12 epitope-mimic peptide B2.1, and the reactivity profile had many similarities but also significant differences from that observed for gp120. The paratope map of b12 may facilitate the design of molecules that are able to elicit b12-like activities.     

Organization of the vesicular stomatitis virus glycoprotein into membrane microdomains occurs independently of intracellular viral components

The glycoprotein (G protein) of vesicular stomatitis virus (VSV) is primarily organized in plasma membranes of infected cells into membrane microdomains with diameters of 100 to 150 nm, with smaller amounts organized into microdomains of larger sizes. This organization has been observed in areas of the infected-cell plasma membrane that are outside of virus budding sites as well as in the envelopes of budding virions. These observations raise the question of whether the intracellular virion components play a role in organizing the G protein into membrane microdomains. Immunogold-labeling electron microscopy was used to analyze the distribution of the G protein in arbitrarily chosen areas of plasma membranes of transfected cells that expressed the G protein in the absence of other viral components. Similar to the results with virus-infected cells, the G protein was organized predominantly into membrane microdomains with diameters of approximately 100 to 150 nm. These results indicate that internal virion components are not required to concentrate the G protein into membrane microdomains with a density similar to that of virus envelopes. To determine if interactions between the G protein cytoplasmic domain and internal virion components were required to create a virus budding site, cells infected with recombinant VSVs encoding truncation mutations of the G protein cytoplasmic domain were analyzed by immunogold-labeling electron microscopy. Deletion of the cytoplasmic domain of the G protein did not alter its partitioning into the 100- to 150-nm microdomains, nor did it affect the incorporation of the G protein into virus envelopes. These data support a model for virus assembly in which the G protein has the inherent property of partitioning into membrane microdomains that then serve as the sites of assembly of internal virion components.     

The SUMO isopeptidase Ulp2 prevents accumulation of SUMO chains in yeast

The ubiquitin-related protein SUMO functions by becoming covalently attached to lysine residues in other proteins. Unlike ubiquitin, which is often linked to its substrates as a polyubiquitin chain, only one SUMO moiety is attached per modified site in most substrates. However, SUMO has recently been shown to form chains in vitro and in mammalian cells, with a lysine in the non-ubiquitin-like N-terminal extension serving as the major SUMO-SUMO branch site. To investigate the physiological function of SUMO chains, we generated Saccharomyces cerevisiae strains that expressed mutant SUMOs lacking various lysine residues. Otherwise wild-type strains lacking any of the nine lysines in SUMO were viable, had no obvious growth defects or stress sensitivities, and had SUMO conjugate patterns that did not differ dramatically from wild type. However, mutants lacking the SUMO-specific isopeptidase Ulp2 accumulated high molecular weight SUMO-containing species, which formed only when the N-terminal lysines of SUMO were present, suggesting that they contained SUMO chains. Furthermore SUMO branch-site mutants suppressed several of the phenotypes of ulp2delta, consistent with the possibility that some ulp2delta phenotypes are caused by accumulation of SUMO chains. We also found that a mutant SUMO whose non-ubiquitin-like N-terminal domain had been entirely deleted still carried out all the essential functions of SUMO. Thus, the ubiquitin-like domain of SUMO is sufficient for conjugation and all downstream functions required for yeast viability. Our data suggest that SUMO can form chains in vivo in yeast but demonstrate conclusively that chain formation is not required for the essential functions of SUMO in S. cerevisiae.