Avian diversity and endemism in Namibia: patterns from the Southern African Bird Atlas Project

Namibia supports a highly diverse avifauna of 644 species, including over 90 species endemic to the southern African subregion and 13 species endemic to the country. Patterns of species diversity in relation to protected areas and habitat types were analysed using data from the Southern African Bird Atlas Project. A modified Shannon index appropriate for atlas data was used to derive an index of diversity for all species, wetland, terrestrial, threatened, and regional endemic species. Species richness for Namibian endemics was mapped. Overall species diversity is highest in the northeast of Namibia where wetland and riparian habitats coincide. Both wetland and terrestrial species show highest diversity in this area. The greatest diversity of southern African endemics falls within the Savanna-Karoo systems. Several key areas are identified for red data species, including the Caprivi Strip, Kunene and Orange Rivers, coastal wetlands and ephemeral river mouths and pans. This highlights the pressures operating on wetland and riparian habitats in arid environments. Concentrations of Namibian endemics are found in the northwestern (Kaoko) escarpment of the country. Although much of the area of high diversity of wetland, terrestrial and red data species falls within protected areas, national and regional endemics are poorly represented within national parks.     

Lurcher GRID2-induced death and depolarization can be dissociated in cerebellar Purkinje cells

The Lurcher mutation transforms the GRID2 receptor into a constitutively opened channel. In Lurcher heterozygous mice, cerebellar Purkinje cells are permanently depolarized, a characteristic that has been thought to be the primary cause of their death, which occurs from the second postnatal week onward. The more dramatic phenotype of Lurcher homozygotes is thought to be due to a simple gene dosage effect of the mutant allele. We have analyzed the phenotype of Lurcher/hotfoot heteroallelic mutants bearing only one copy of the Lurcher allele and no wild-type Grid2. Our results show that the absence of wild-type GRID2 receptors in these heteroallelic mutants induces an early and massive Purkinje cell death that is correlated with early signs of autophagy. This neuronal death is independent of depolarization and can be explained by the direct activation of autophagy by Lurcher GRID2 receptors through the recently discovered signaling pathway formed by GRID2, n-PIST, and Beclin1.     

A novel yeast expression system for the overproduction of quality-controlled membrane proteins

Saturation of the cell's protein folding capacity and accumulation of inactive incompletely folded protein often accompanying the overexpression of membrane proteins (MPs) presents an obstacle to their efficient purification in a functional form for structural studies. We present a novel strategy for optimization of functional MP expression in Saccharomyces cerevisiae. This approach exploits the unfolded protein response (UPR) pathway, a stress signaling mechanism that senses the accumulation of unfolded proteins in the endoplasmic reticulum. We demonstrate that a high level of UPR induction upon expression of a MP reflects impaired functional expression of that protein. Tuning the expression level of the protein so as to avoid or minimize UPR induction results in its increased functional expression. UPR status can therefore serve as a proxy variable for the extent of impaired expression of a MP that may even be applicable in the absence of knowledge of the protein's biological function.     

Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes

The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with mitochondrial membranes and is not extracted with hypotonic or hypertonic media or with nonionic detergents. Some solubilization was obtained with bile salt solutions, but the zwitter-ionic detergent. Miranol H2M, was most effective in extracting the enzyme. The Miranol extracts were fractionated by column chromatography on Bio-Gel A-1.5 m. The solubilized enzyme is considerably more active in converting unsaturated than saturated phosphatidyl-glycerols, but shows little preference for the cytidine diphosphate diacylglycerols with different fatty acyl substituents. There is an absolute dependence upon divalent cations with the order of effectiveness: Co2+ much greater than Mn2+ greater than Mg2+. In the presence of optimal levels of Co2+ other divalent cations are inhibitory with the order of inhibition: Cd2+ greater than Zn2+ greater than Ca2+ greater than Ba2+ greater than Cu2+ greater than Hg2+ greater than Ni2+. The solubilized enzyme exhibited no requirement for added phospholipids and several phospholipids inhibited the reaction in the order: diphosphatidylglycerol greater than phosphatidylethanolamine greater than phosphatidylserine greater than phosphatidylinositol.     

Structural and enzymatic studies of the T4 DNA replication system. I. Physical characterization of the polymerase accessory protein complex

In this study, we have investigated the structural and physical properties of the bacteriophage T4 DNA polymerase accessory proteins. We find that T4 gene 44 and 62 proteins associate to form a tight, highly homogeneous complex, containing four gene 44 protein subunits and one gene 62 protein subunit. The molecular mass of the complex is 163,700 daltons. Sedimentation results suggest that the complex is quite asymmetric, with a prolate ellipsoid axial ratio of about 5:1. This protein complex is known to carry a DNA-dependent ATPase activity; we show by photoaffinity labeling that the ATP-binding sites reside in the gene 44 protein subunits of the complex. Equilibrium sedimentation and chemical cross-linking studies indicate that the T4 gene 45 protein self-associates to form a trimer in solution. This trimer species also appears to be quite asymmetric, showing an axial ratio for a prolate ellipsoid of about 6:1, assuming normal hydration.     

Engineering lepidopteran insect cells for sialoglycoprotein production by genetic transformation with mammalian beta 1,4-galactosyltransferase and alpha 2,6-sialyltransferase genes

Recombinant mammalian glycoproteins produced by the baculovirus-insect cell expression system usually do not have structurally authentic glycans. One reason for this limitation is the virtual absence in insect cells of certain glycosyltransferases, which are required for the biosynthesis of complex, terminally sialylated glycoproteins by mammalian cells. In this study, we genetically transformed insect cells with mammalian beta 1,4-galactosyltransferase and alpha 2,6-sialyltransferase genes. This produced a new insect cell line that can express both genes, serve as hosts for baculovirus infection, and produce foreign glycoproteins with terminally sialylated N-glycans.     

Dilemmas in international research and the value of practical wisdom

When conducting research in an international setting, in a country different than that of the researcher, unpredictable circumstances can arise. A study conducted by a novice North American researcher with a vulnerable population in northern Ghana highlights these happenings with an emphasis placed on the ethical challenges encountered. An illustration from the research is used to highlight an ethical dilemma while in the field, and how utilizing a moral decision‐making framework can assist in making choices about a participant's right to autonomy, privacy, and confidentiality during the research process. Moral frameworks, however, can never be enough to solve a dilemma since guidelines only describe what to aim for and not how to interpret or use them. Researchers must therefore strive to move beyond these frameworks to employ practical wisdom or phronesis so to combine the right thing to do with the skill required to figure out what the right choice is. The skill of practical wisdom must be acquired because without it international researchers indecisively fumble around with good intentions, often leaving a situation in worse shape than they found it.     

Instability of rRNA operons in Bacillus subtilis.

Many laboratory strains of Bacillus subtilis contain 9 rather than 10 rRNA operons due to deletions occurring within the rrnJ-rrnW or rrnI-rrnH-rrnG gene cluster. These operons are members of two sets of closely spaced clusters located in the cysA-aroI region. Analysis of rescued DNA from integrants with insertions into rrnG and rrnH indicated that these tandemly arranged operons allowed frequent deletions of an rrn operon equivalent. These events may arise spontaneously by intrachromosomal recombination or by simultaneous double crossovers with a multimeric integrative plasmid.