Tau self-association: stabilization with a chemical cross-linker and modulation by phosphorylation and oxidation state

tau is a major component of paired helical filaments found in the neurofibrillary tangles of Alzheimer's diseased brain. However, the mechanism or mechanisms responsible for the association of tau to form these aggregates remains unknown. In this study, the role of intermolecular disulfide bonds in the formation of higher order oligomers of bovine tau and the human recombinant tau isoform T3 was examined using the chemical cross-linking agent disuccinimidylsuberate (DSS). In addition, the role of phosphorylation and oxidation state on the in vitro self-association of tau was studied using this experimental model. Stabilization of tau-tau interactions with DSS indicated that intermolecular disulfide bonds probably play a predominant role in dimer formation, but the formation of higher order oligomers of tau cannot be attributed to these bonds alone. tau-tau interactions were significantly decreased either by blocking Cys residues or by exposing the tau to a reducing (nitrogen and dithiothreitol), instead of an oxidizing, environment. tau self-association was also significantly decreased by prior phosphorylation with calcium/calmodulin-dependent protein kinase II. Phosphorylation by cyclic AMP-dependent protein kinase or dephosphorylation by alkaline phosphatase did not alter tau self-assembly. These data suggest a role for several factors that may modulate tau self-association in vivo.     

Clarification of the relationship between free radical spin trapping and carbon tetrachloride metabolism in microsomal systems

It has been proposed that the C-phenyl-N-tert-butylnitrone/trichloromethyl radical adduct (PBN/.CCl3) is metabolized to either the C-phenyl-N-tert-butylnitrone/carbon dioxide anion radical adduct (PBN/.CO2-) or the glutathione (GSH) and CCl4-dependent PBN radical adduct (PBN/[GSH-.CCl3]). Inclusion of PBN/.CCl3 in microsomal incubations containing GSH, nicotinamide adenine dinucleotide phosphate (NADPH), or GSH plus NADPH produced no electron spin resonance (ESR) spectral data indicative of the formation of either the PBN/[GSH-.CCl3] or PBN/.CO2- radical adducts. Microsomes alone or with GSH had no effect on the PBN/.CCl3 radical adduct. Addition of NADPH to a microsomal system containing PBN/.CCl3 presumably reduced the radical adduct to its ESR-silent hydroxylamine because no ESR signal was observed. The Folch extract of this system produced an ESR spectrum that was a composite of two radicals, one of which had hyperfine coupling constants identical to those of PBN/.CCl3. We conclude that PBN/.CCl3 is not metabolized into either PBN/[GSH-.CCl3] or PBN/.CO2- in microsomal systems.     

What are the consequences of the new American guidelines for the diagnosis of diabetes mellitus in The Netherlands?

Anaemia is a commonly encountered medical condition, although associated ophthalmic manifestations are not often sought or recognised. The authors present a case report of a patient with severe vitamin B12 deficiency anaemia with florid retinal changes classical of anaemic retinopathy. A review of the ocular involvement in anaemia is also presented.     

Recognition of chitin and proteins in invertebrate cuticles using analytical pyrolysis/gas chromatography and pyrolysis/gas chromatography/mass spectrometry

Flash pyrolysis/gas chromatography (py/GC) and py/GC/mass spectrometry (MS) have been utilized to characterize the cuticles of invertebrates chemically. Pyrolysis products have been identified and assigned to specific cuticular components. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones are proposed as characteristic pyrolysis markers for chitin. Pyrolysis products displaying ions of m/z 70, 154, 168, 194 are thought to derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. These products, constituting specific pyrolysis markers for invertebrate cuticles, may reflect the amino acid composition of their constituent structural proteins. The source of the various pyrolysis products of proteins has been verified by pyrolysis of reference proteins, peptides and amino acid mixtures. The presence of additional pyrolysis products related directly to histidine and catechol moieties is consistent with the chemical structure and composition proposed for arthropod cuticles based on recent work utilizing solid state 13C and 15N nuclear magnetic resonance. This study constitutes the first comprehensive chemical characterization of the pyrolysis products of invertebrate cuticles and provides the basis for future investigations requiring qualitative screening for cross-linked chitin and proteins in modern and fossil cuticles and in materials, e.g. geopolymers, that may be derived from them.     

Support for school-based sexuality education among South Carolina voters

A random-digit dialed telephone survey was conducted in a traditionally conservative southern state to determine the level of support for sexuality education in the public schools including support for specific sexuality education topics, the earliest grade level at which each topic should be taught, and the amount of instruction time required for sexuality education in the high schools. Survey data were obtained from 534 South Carolina registered voters in late January/early February 1997. Results demonstrated that most South Carolina registered voters: 1) supported sexuality education in the public schools; 2) supported instruction on a variety of sexuality education topics; 3) supported instruction at all grade levels, especially beginning in middle school; and 4) believed instruction time for sexuality education in the high schools should either remain the same or be increased. In addition, a significant increase in support for sexuality education occurred from the beginning of the survey to the end, suggesting that the instrument itself may have served as an educational tool for respondents. The characteristics of registered voters who supported sexuality education at the beginning of the survey and at the end were examined and compared. These results may assist in the development of educational and marketing strategies designed to build support for school-based sexuality education programs in South Carolina and elsewhere.     

Diamniotic placentation associated with omphalopagus conjoined twins: implications for a contemporary model of conjoined twinning

We have studied omphalopagus conjoined twins with a diamniotic monochorionic placenta. Although conjoined twins usually present in a single amniotic sac, one other example of diamniotic placenta has been reported in omphalopagus twins [Weston et al., 1990: Am J Med Genet 37:558-561]. Most theories concerning the pathogenesis of conjoined twinning exclude the possibility of diamniotic placentation. However, Spencer [1992: Teratology 45:591-602] recently elaborated a model for conjoined twinning based on duplication of organizing centers (primitive streaks) during gastrulation. We have considered the fate of embryonic membranes according to this model of omphalopagus twinning and show that diamniotic placentation is a predictable outcome.