The Apolipoprotein E/CI/CII Gene Cluster and Late-Onset Alzheimer Disease

The chromosome 19 apolipoprotein E/CI/CII gene cluster was examined for evidence of linkage to a familial Alzheimer disease (FAD) locus. The family groups studied were Volga German (VG), early-onset non-VG (ENVG; mean age at onset <60 years), and late-onset families. A genetic association was observed between apolipoprotein E (ApoE) allele ε4 and FAD in late-onset families; the ε4 allele frequency was .51 in affected subjects, .37 in at-risk subjects, .11 in spouses, and .19 in unrelated controls. The differences between the ε4 frequencies in affected subjects versus controls and in at-risk subjects versus controls were highly significant (standard normal deviate [Z_SND]) = 7.37, P < 10⁻⁹; and Z_SND = 4.07, P < .00005, respectively). No association between the ε4 allele and FAD was observed in the ENVG or VG groups. A statistically significant allelic association between ε4 and AD was also observed in a group of unrelated subjects; the ε4 frequency was .26 in affected subjects, versus .19 in controls (Z_SND = 2.20, P < .03). Evidence of linkage of ApoE and ApoCII to FAD was examined by maximum-likelihood methods, using three models and assuming autosomal dominant inheritance: (1) age-dependent penetrance, (2) extremely low (1%) penetrance, and (3) age-dependent penetrance corrected for sporadic Alzheimer disease (AD). For ApoCII in late-onset families, results for close linkage were negative, and only small positive lod-score-statistic (Z) values were obtained (model 1, maximum Z [Z_max] = 0.61, recombination fraction [θ] = .30; model 2, Z_max = 0.47, θ = .20). For ApoE in late-onset kindreds, positive Z values were obtained when either allele frequencies from controls (model 1, Z_max = 2.02, θ = .15; model 2, Z_max = 3.42, θ = .05) or allele frequencies from the families (model 1, Z_max = 1.43, θ = .15; model 2, Z_max = 1.70, θ = .05) were used. When linkage disequilibrium was incorporated into the analysis, the Z values increased (model 1, Z_max = 3.17, θ = .23; model 3, Z_max = 1.85, θ = .20). For the ENVG group, results for ApoE and ApoCII were uniformly negative. Affected-pedigree-member analysis gave significant results for the late-onset kindreds, for ApoE (Z_SND = 3.003, P = .003) and ApoCII (Z_SND = 2.319, P = .016), when control allele frequencies were used but not when allele frequencies were derived from the families.     

Design and sample-size considerations in the detection of linkage disequilibrium with a disease locus.

The presence of linkage disequilibrium between closely linked loci can aid in the fine mapping of disease loci. We investigate the power of several designs for sampling individuals with different disease genotypes. As expected, haplotype data provide the greatest power for detecting disequilibrium, but, in the absence of parental information to resolve the phase of double heterozygotes, the most powerful design samples only individuals homozygous at the trait locus. For rare diseases, such a scheme is generally not feasible, and we also provide power and sample-size calculations for designs that sample heterozygotes. The results provide information useful in planning disequilibrium studies.     

Spectral transitions of nitrosyl hemes during ligand binding to hemoglobin.

Human deoxyhemoglobin has been titrated with nitric oxide at several pH values ranging from 6.0 to 9.0, in the presence and absence of the allosteric effector inositol hexaphosphate at 25 degrees C. Samples were frozen for EPR measurements or analyzed optically within 30 s after mixing to ensure a kinetic population of intermediates. Fractions of pentacoordinate alpha-NO heme groups were determined by fitting EPR and absorbance difference spectra in terms of linear combinations of standard signals. Equivalent results were obtained by these techniques. The fraction of alpha-NO heme exhibiting pentacoordinate character in Hb4NO increases from 0.07 to 0.73 in going from pH 9 to 6. The fraction of alpha hemes which are pentacoordinate in fully saturated nitrosyl hemoglobin, Hb4(NO), increases from 0.0 to 0.41 over the same pH range. Only in the presence of bound inositol-P6 are all 4 the alpha-NO hemes pentacoordinate. Thus, the expression of modified NO heme character is not simply a reflection of the formation of low affinity quaternary conformations. Rather, within this conformation the alpha chain iron atoms exhibit an equilibrium between hexa- and pentacoordinate structures which is perturbed markedly by both proton and phosphate binding. No intermediate coordination structure of the type suggested by Chevion et al. (Chevion, M., Stern, A., Peisach, J., Blumberg, W.E., and Simon, S. (1978) Biochemistry 17, 1745-1750) appears to occur since the observed alpha-NO heme spectra can always by represented quantitatively as a linear combination of the normal hexacoordinate and pentacoordinate signals. The formation of pentacoordinate alpha-NO causes this subunit to exhibit a higher affinity for nitric oxide. Thus on standing at low levels of saturation, there is a slow (t1/2 approximately equal to 8 min at pH 7, 25 degrees C) re-equilibration of ligand from beta to alpha subunits. The final ratio of alpha-NO to beta-NO is 2 to 1 in the absence of phosphates and greater than 10 to 1 in the presence of inositol hexaphosphate.     

Role of plasmids in mercury transformation by bacteria isolated from the aquatic environment.

Eight mercury-resistant bacterial strains isolated from the Chesapeake Bay and one strain isolated from the Cayman Trench were examined for ability to volatilize mercury. Mercury volatilization was found to be variable in the strains tested. In addition, plasmids were detected in all strains. After curing, two of the bacterial strains lost mercury resistance, indicating that volatilization is plasmid mediated in these strains. Only two cultures demonstrated ability to methylate mercuric chloride under either aerobic or anaerobic conditions. Methylation of mercury, compared with volatilization, appears to be mediated by a separate genetic system in these bacteria. It is concluded that mercury volatilization in the estuarine environment can be mediated by genes carried on plasmids.     

Sequence-specific DNA-protein interaction: the lac represser

A model is proposed for lac repressor-lac operator binding which accounts for the tetrameric subunit structure of the lac repressor and for factors involved in the strength, specificity and regulation of repressor-operator interaction. The model employs a π-helix in the amino terminal 25 residues of the lac repressor whereby three tyrosine residues of each subunit intercalate between base pairs of the lac operator. For the outer palindromic sequences of the operator, base specificity is provided by amino acids adjacent to the carboxyl sides of the tyrosine residues of two of the subunits. The inner palindromic sequences which bind the other two subunits form stems of hairpin loops in the operator. Base specificity for these two subunits is provided by amino acids adjacent to the amino sides of the tyrosine residues. In addition to 12 intercalated tyrosine residues, the model provides for a total of at least eight electrostatic interactions and ten sequence-specific hydrogen bonds.     

The isolation and identification of a novel intermediate in ubiquinone-6 biosynthesis by Saccharomyces cerevisiae.

The reaction product obtained from HeLa cell nuclei incubated with [³H]NAD was specifically hydrolyzed with snake venom phosphodiesterase. Analysis of the hydrolyzed product revealed that it is a homopolymer consisting of 4–5 repetition of ADP-ribose units. The [³H]poly ADP-ribosylated histone fraction was anslyzed by urea-acetic acid polyacrylamide gel electrophoresis. The radioactive peak was clearly separated from the stained histone H1 band, while a slight overlap was observed. When chromatographed on a SP-Sephadex C-50 column, more than 90% of the radioactivity of [³H]poly(ADP-ribose) was eluted in accordance with histones but not with nonhistone contaminants. On a sodium dodecyl sulfate polyacrylamide gel electrophoresis, a major radioactive peak appeared at a position very close to the histone Hl band, which disappeared by the treatment with alkali prior to electrophoresis. A selective extraction of histone Hl with 5% perchloric acid showed that histone Hl contained about 85% of the radioactivity incorporated into whole histones.     

Restricted dietary protein in pregnant beef cows: I. The effect on length of gestation and calfhood mortality

Beef cows fed 0.37 Kg crude protein/day during the last four months of pregnancy had significantly shortened gestation (274 days vs. 282 days) and decreased weight gain (25 Kg vs. 66 Kg) compared to control cows fed 0.96 Kg crude protein/day. Calf mortality in the low protein group was associated with either dystocia (3 calves) or prematurity (2 calves). There were no deaths among control calves. It is suggested that protein malnutrition in late pregnancy may be a contributing factor to neonatal mortality among beef calves.     

Vascular organization of the catfish gill filament

Summary Light and scanning electron microscopic observations were made on methyl-methacrylate corrosion casts of the blood vessels in the gills of channel catfish (Ictalurus punctatus). The vasculature of the gill filament can be divided into three distinct pathways: 1. the well-known respiratory circulation which includes the afferent filamental artery (AF), afferent lamellar arteriole (AL), lamella (L), efferent lamellar arteriole (EL) and efferent filamental artery (EF), 2. a nutritive pathway from the EF through small nutritive capillaries (NC) and into one of several filamental veins (FV), and 3. an interlamellar circulation in which small prelamellar arterio-venous anastomoses (PAVA) connect the AL into a series of organized vascular spaces (interlamellar vessels, ILV's) that underlie the interlamellar filamental epithelium. Several sinuslike spaces associated with AF, EF and the filamental cartilagenous support were also observed. The physiological significance of these vascular pathways is discussed.Supported in part by NSF Grant No. PCM 76-16840The authors wish to acknowledge the assistance of Mr. P. Holbert, Miss K. Drajus and Mrs. J. Smith. Gratitude is expressed by Kenneth R. Olson to Dr. Janice Nowell for her helpful suggestions with corrosion casting techniques