Evidence of an absence: the genetic origins of the 1918 pandemic influenza virus

Annual outbreaks of influenza A infection are an ongoing public health threat and novel influenza strains can periodically emerge to which humans have little immunity, resulting in devastating pandemics. The 1918 pandemic killed at least 40 million people worldwide and pandemics in 1957 and 1968 caused hundreds of thousands of deaths. The influenza A virus is capable of enormous genetic variation, both by continuous, gradual mutation and by reassortment of genome segments between viruses. Both the 1957 and 1968 pandemic strains are thought to have originated as reassortants in which one or both human-adapted viral surface proteins were replaced by proteins from avian influenza strains. Analyses of the genes of the 1918 pandemic virus, however, indicate that this strain might have had a different origin. The haemagglutinin and nucleoprotein genome segments in particular are unlikely to have come directly from an avian source that is similar to those that are currently being sequenced. Determining whether a pandemic influenza virus can emerge by different mechanisms will affect the scope and focus of surveillance and prevention efforts.     

Quantitative studies of cell-bubble interactions and cell damage at different pluronic F-68 and cell concentrations

Pluronic F-68 (PF-68) is routinely used as a shear-protection additive in mammalian cell cultures. However, most previous studies of its shear protection mechanisms have typically been qualitative in nature and have not covered a wide range of PF-68 and cell concentrations. In this study, interactions between air bubbles along with the associated cell damage were investigated using the novel adenovirus-producing cell line PER.C6, a human embryonic retinoblast transfected with the adenovirus type 5 E1 gene. A wide range of PF-68 and cell concentrations (approximately 3 orders of magnitude) were used in these studies. At low PF-68 concentrations (0.001 g/L), cells had a very high affinity for bubbles, indicated by a more than 10-fold increase in cell concentration in the foam layer liquid versus the bulk liquid. At high PF-68 concentrations ( approximately 3 g/L), however, the cell concentration in the foam layer liquid was only approximately 40% of that in the bulk cell suspension. The number of cells associated with each bubble decreased from approximately 1000 cells at 0.001 g/L PF-68 to approximately 120 cells at 3 g/L PF-68. Despite the lower cell affinity for bubbles at a high PF-68 concentration, at high cell concentrations (10(7) cells/mL and 1 g/L PF-68) significant cell entrapment occurred in the foam layer, on the order of 1000 cells/bubble. For the cells carried by the bubbles, quantitative cell damage data revealed that the probability of cell death from bubble rupture was independent of bulk cell concentration but was affected by PF-68 concentration. These quantitative studies further indicated that even at a low PF-68 concentration of 0.03 g/L, approximately 30% of the attached cells were killed during the bubble rupture process. At the same time, at low PF-68 concentration (<0.1 g/L), significant cell death occurred prior to bubble rupture. On average, a bubble disrupted more cells in the bulk liquid and/or foam layer than during rupture. For both mechanisms, the number of cells damaged by each bubble increased with decreasing PF-68 concentration and increasing bulk cell concentration.     

Evolution of pigment cell regression in the cavefish Astyanax: a late step in melanogenesis

Pigmentation and eyes are often lost in cave-adapted animals. Although the mechanisms of eye degeneration are beginning to be understood, little is known about the evolutionary and developmental processes involved in pigment cell regression. In teleost embryos, a population of neural crest cells migrates into the body wall and differentiates into melanophores, xanthophores, and iridophores. All three pigment cell types are present in the eyed surface-dwelling form (surface fish) of the teleost Astyanax mexicanus. However, melanophores are absent or substantially reduced in number in various derived populations of the conspecific blind cave-dwelling form (cavefish). We show here that tyrosinase-positive melanoblasts are present in cavefish. DiI labeling revealed a population of trunk neural crest cells in cavefish embryos that migrate to locations normally occupied by differentiated melanophores. We also discovered a cell population in cavefish embryos and adults resembling melanoblasts in several features, including the ability to synthesize melanin when supplied with the tyrosinase substrate l-dopa. DiI-tyrosinase double-labeling and neural keel explant experiments showed that the tyrosinase-positive cells are derived from the neural crest. The number of melanoblasts varies in different adult cavefish populations relative to the extent of melanophore reduction. Although cavefish melanoblasts can synthesize melanin from exogenous l-dopa, they are unable to convert exogenous l-tyrosine to l-dopa and melanin. We conclude that pigment cell regression in cavefish is mediated by an evolutionary change late in melanogenesis that may involve an impediment in the ability to convert l-tyrosine to l-dopa and melanin.     

Enzyme activity--it's all about image

Unraveling the functional roles of proteins is a major challenge facing the postgenome researcher. Advances towards this goal have been made through the development of both chemical and biochemical tools for monitoring protein activity. Recently, a myriad of fluorescence-based imaging tools have emerged for in vitro, in vivo and whole animal applications. These tools have provided methods to monitor the spatial and temporal distribution of proteins and bioorganic molecules dynamically. Here, recent advances in chemical and biochemical techniques that allow the detection of enzymatic activity within intact cells and in vivo are reviewed. Such technologies have the potential to be integrated into drug-development programs to facilitate both the functional validation of pharmaceutical targets and the treatment of human disease.     

Murid herpesvirus 4 strain 68 M2 protein is a B-cell-associated antigen important for latency but not lymphocytosis

This work describes analyses of the function of the murid herpesvirus 4 strain 68 (MHV-68) M2 gene. A frameshift mutation was made in the M2 open reading frame that caused premature termination of translation of M2 after amino acid residue 90. The M2 mutant showed no defect in productive replication in vitro or in lungs after infection of mice. Likewise, the characteristic transient increase in spleen cell number, Vbeta4 T-cell-receptor-positive CD8(+) T-cell mononucleosis, and establishment of latency were unaffected. However, the M2 mutant virus was defective in its ability to cause the transient sharp rise in latently infected cells normally seen in the spleen after infection of mice. We also demonstrate that expression of M2 is restricted to B cells in the spleen and that M2 encodes a 30-kDa protein localizing predominantly in the cytoplasm and plasma membrane of B cells.     

Amyloid as a natural product

Amyloid fibrils, such as those found in Alzheimer's and the gelsolin amyloid diseases, result from the misassembly of peptides produced by either normal or aberrant intracellular proteolytic processing. A paper in this issue by Marks and colleagues (Berson et al., 2003) demonstrates that intra-melanosome fibrils are formed through normal biological proteolytic processing of an integral membrane protein. The resulting peptide fragment assembles into fibrils promoting the formation of melanin pigment granules. These results, along with the observation that amyloid fibril formation by bacteria is highly orchestrated, suggest that fibril formation is an evolutionary conserved biological pathway used to generate natural product nanostructures.     

A microplate assay specific for the enzyme aggrecanase

We have identified a 41-residue peptide, bracketing the aggrecanase cleavage site of aggrecan, that serves as a specific substrate for this enzyme family. Biotinylation of the peptide allowed its immobilization onto streptavidin-coated plates. Aggrecanase-mediated hydrolysis resulted in an immobilized product that reveals an N-terminal neoepitope, recognized by the specific antibody BC-3. This assay is highly specific for aggrecanases; MMPs were inactive in this assay. Reduction of the peptide size below 30 amino acids resulted in a significant diminution of activity. Using the immobilized 41-residue peptide as a substrate, we have developed a 96-well microplate-based assay that can be conveniently used for high-throughput screening of samples for aggrecanase activity and for discovery of inhibitors of aggrecanase activity.     

Cys10 mixed disulfides make transthyretin more amyloidogenic under mildly acidic conditions

Conservative mutation of transthyretin's surface residues can predispose an individual to familial amyloidosis by dramatically changing the energetics of misfolding. Senile systemic amyloidosis (SSA), however, cannot be explained in this fashion because wild-type (WT) transthyretin (TTR) misfolds and misassembles into amyloid. Since various modifications of the SH functionality of Cys10 have been reported in humans, we sought to understand the extent to which these modifications alter the stability and amyloidosis of WT TTR as a possible explanation for SSA. Homotetrameric Cys10 TTR variants, including TTR-Cys, TTR-GSH, TTR-CysGly, and S-sulfonated TTR, were chemically synthesized starting with WT TTR. The TTR-Cys, TTR-GSH, and TTR-CysGly isoforms are more amyloidogenic than WT at the higher end of the acidic pH range (pH 4.4-5.0), and they are similarly destabilized relative to WT TTR toward urea denaturation. They exhibit rates of urea-mediated tetramer dissociation (pH 7) and MeOH-facilitated fibril formation similar to those of WT TTR. Under mildly acidic conditions (pH 4.8), the amyloidogenesis rates of the mixed disulfide TTR variants are much faster than the WT rate. S-Sulfonated TTR is less amyloidogenic and forms fibrils more slowly than WT under acidic conditions, yet it exhibits a stability and rates of tetramer dissociation similar to those of WT TTR when subjected to urea denaturation. Conversion of the Cys10 SH group to a mixed disulfide with the amino acid Cys, the CysGly peptide, or glutathione increases amyloidogenicity and the amyloidogenesis rate above pH 4.6, conditions under which TTR probably forms fibrils in humans. Hence, these modifications may play an important role in human amyloidosis.