Associations between White Matter Hyperintensities and β Amyloid on Integrity of Projection,Association, and Limbic Fiber Tracts Measured with Diffusion Tensor MRI

The goal of this study was to assess the relationship between Aβ deposition and white matter pathology (i.e., white matter hyperintensities, WMH) on microstructural integrity of the white matter. Fifty-seven participants (mean age: 78±7 years) from an ongoing multi-site research program who spanned the spectrum of normal to mild cognitive impairment (Clinical dementia rating 0–0.5) and low to high risk factors for arteriosclerosis and WMH pathology (defined as WMH volume >0.5% total intracranial volume) were assessed with positron emission tomography (PET) with Pittsburg compound B (PiB) and magnetic resonance and diffusion tensor imaging (DTI). Multivariate analysis of covariance were used to investigate the relationship between Aβ deposition and WMH pathology on fractional anisotropy (FA) from 9 tracts of interest (i.e., corona radiata, internal capsule, cingulum, parahippocampal white matter, corpus callosum, superior longitudinal, superior and inferior front-occipital fasciculi, and fornix). WMH pathology was associated with reduced FA in projection (i.e., internal capsule and corona radiate) and association (i.e., superior longitudinal, superior and inferior fronto-occipital fasciculi) fiber tracts. Aβ deposition (i.e., PiB positivity) was associated with reduced FA in the fornix and splenium of the corpus callosum. There were interactions between PiB and WMH pathology in the internal capsule and parahippocampal white matter, where Aβ deposition reduced FA more among subjects with WMH pathology than those without. However, accounting for apoE ε4 genotype rendered these interactions insignificant. Although this finding suggests that apoE4 may increase amyloid deposition, both in the parenchyma (resulting in PiB positivity) and in blood vessels (resulting in amyloid angiopathy and WMH pathology), and that these two factors together may be associated with compromised white matter microstructural integrity in multiple brain regions, additional studies with a longitudinal design will be necessary to resolve this issue.     

Comparative responses of Achillea millefolium ecotypes to competition and soil type

Summary Achillea millefolium populations from adjacent sites with zonal and serpentime soil were used to test predictions about the relation between growth and the competitive ability of plants in productive and unproductive environments. Under greenhouse conditions, individually-grown plants from both sources grew larger in serpentine soil than in zonal soil; serpentine plants accumulated 72% more biomass than zonal plants. In zonal soil, zonal plants were 71% larger than serpentine plants, although these differences were not statistically significant, and plants from both sources accumulated much less biomass and were shorter than plants growing in serpentine soil. In a high density, fertilized replacement series, zonal plants were taller and heavier but exhibited no more competitive ability than serpentine plants. The predictions that rapid height growth and biomass accumulation contribute significantly to competitive ability are not supported by our results. Although ecotypic differentiation has occurred between these A. millefolium populations, apparently in response to different soil types, the expression of these heritable differences can be masked by other environmental effects. There has been no apparent trade-off in these ecotypes between their response to the physical environment and their competitive ability.     

Kinetic parameters of the protein tyrosine kinase activity of EGF-receptor mutants with individually altered autophosphorylation sites.

Epidermal growth factor (EGF)-receptor mutants in which individual autophosphorylation sites (Tyr1068, Tyr1148 or Tyr1173) have been replaced by phenylalanine residues were expressed in NIH-3T3 cells lacking endogenous EGF-receptors. Kinetic parameters of the kinase of wild-type and mutant receptors were compared. Both wild-type and mutant EGF-receptors had a Km(ATP) 1-3 microM for the autophosphorylation reaction, and a Km(ATP) of 3-7 microM for the phosphorylation of a peptide substrate. These are similar to the Km(ATP) values reported for EGF-receptor of A431 cells. A synthetic peptide representing the major in vitro autophosphorylation site Tyr1173 of the EGF-receptor (KGSTAENAEYLRV) was phosphorylated by wild-type receptor with a Km of 110-130 microM, and the peptide inhibited autophosphorylation with a Ki of 150 microM. Mutant EGF-receptors phosphorylated the peptide substrate with a Km of 70-100 microM. A similar decrease of Km (substrate) was obtained when the phosphorylation experiments were performed with the commonly applied substrates angiotensin II and a peptide derived from c-src. The Km of angiotensin II phosphorylation was reduced from 1100 microM for wild-type receptor to 890 microM for mutant receptor and for c-src peptide from 1010 microM to 770 microM respectively. The Vmax of the kinase was dependent on receptor concentration, but was not significantly affected by the mutation. Analogs of the Tyr1173 peptide in which the tyrosine residue was replaced by either a phenylalanine or an alanine residue also inhibited autophosphorylation with Ki of 650-750 microM. These analyses show that alterations of individual autophosphorylation sites do not have a major effect on kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of cardiopulmonary baroreflexes during dynamic exercise

To examine the role of cardiopulmonary (CP) mechanoreceptors in the regulation of arterial blood pressure during dynamic exercise in humans, we measured mean arterial pressure (MAP), cardiac output (Q), and forearm blood flow (FBF) during mild cycle ergometer exercise (77 W) in 14 volunteers in the supine position with and without lower-body negative pressure (LBNP). During exercise, MAP averaged 103 +/- 2 mmHg and was not altered by LBNP (-10, -20, or -40 mmHg). Steady-state Q during exercise was reduced from 10.2 +/- 0.5 to 9.2 +/- 0.5 l/min (P less than 0.05) by application of -10 mmHg LBNP, whereas heart rate (97 +/- 3 beats/min) was unchanged. MAP was maintained during -10 mmHg LBNP by an increase in total systemic vascular resistance (TSVR) from 10.3 +/- 0.5 to 11.4 +/- 0.6 U and forearm vascular resistance (FVR) from 17.5 +/- 1.9 to 23.3 +/- 2.6 U. The absence of a reflex tachycardia or reduction in arterial pulse pressure during -10 mmHg LBNP supports the hypothesis that the increase in TSVR and FVR results primarily from the unloading of CP mechanoreceptors. Because CP mechanoreceptor unloading during exercise stimulates reflex circulatory adjustments that act to defend the elevated MAP, we conclude that the elevation in MAP during exercise is regulated and not merely the consequence of differential changes in Q and TSVR. In addition, a major portion of the reduction in FBF in our experimental conditions occurs in the cutaneous circulation. As such, these data support the hypothesis that CP baroreflex control of cutaneous vasomotor tone is preserved during mild dynamic exercise.     

Residues critical for retroviral integrative recombination in a region that is highly conserved among retroviral/retrotransposon integrases and bacterial insertion sequence transposases.

Our comparison of deduced amino acid sequences for retroviral/retrotransposon integrase (IN) proteins of several organisms, including Drosophila melanogaster and Schizosaccharomyces pombe, reveals strong conservation of a constellation of amino acids characterized by two invariant aspartate (D) residues and a glutamate (E) residue, which we refer to as the D,D(35)E region. The same constellation is found in the transposases of a number of bacterial insertion sequences. The conservation of this region suggests that the component residues are involved in DNA recognition, cutting, and joining, since these properties are shared among these proteins of divergent origin. We introduced amino acid substitutions in invariant residues and selected conserved and nonconserved residues throughout the D,D(35)E region of Rous sarcoma virus IN and in human immunodeficiency virus IN and assessed their effect upon the activities of the purified, mutant proteins in vitro. Changes of the invariant and conserved residues typically produce similar impairment of both viral long terminal repeat (LTR) oligonucleotide cleavage referred to as the processing reaction and the subsequent joining of the processed LTR-based oligonucleotides to DNA targets. The severity of the defects depended upon the site and the nature of the amino acid substitution(s). All substitutions of the invariant acidic D and E residues in both Rous sarcoma virus and human immunodeficiency virus IN dramatically reduced LTR oligonucleotide processing and joining to a few percent or less of wild type, suggesting that they are essential components of the active site for both reactions.(ABSTRACT TRUNCATED AT 250 WORDS)     

MSA-35: a protein identified by human autoantibodies that colocalizes with microtubules.

We have identified a putative 35-kilodalton protein that colocalizes with microtubules and displays a unique spatial and temporal distribution during the cell cycle of HeLa cells. This protein has been given the designation MSA-35. MSA-35 first appears in association with microtubules and centrosomes of interphase cells exhibiting centrosome separation as a prelude to cell division. This protein is found in conjunction with kinetochore microtubules throughout their appearance. MSA-35 transiently associates with interpolar microtubules following anaphase and the pattern of MSA-35 reactivity in telophase cells suggests that there are at least seven domains within the intercellular bridge. The distribution of MSA-35 during and following recovery from mitotic arrest with nocodazole suggest that it is also present at low levels in interphase cells, can associate with interphase centrosomes, and colocalizes with nascent microtubules. The complex spatial and temporal distribution of MSA-35 indicates that it may be necessary for a series of events in the mitotic process such as the bundling of microtubules.     

The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.     

A membrane-bound diacylglycerol kinase that selectively phosphorylates arachidonoyl-diacylglycerol. Distinction from cytosolic diacylglycerol kinase and comparison with the membrane-bound enzyme from Escherichia coli

The membrane-bound diacylglycerol kinase from Swiss 3T3 cells (M-DG kinase) was characterized with a mixed micellar assay system, and compared with the cytosolic diacylglycerol kinase from 3T3 cells and with the membrane-bound diacylglycerol kinase from Escherichia coli. M-DG kinase selectively phosphorylated arachidonoyl-diacylglycerols, at a rate 2- to 8-fold higher than that for other naturally occurring long-chain diacylglycerols. In contrast, the cytosolic 3T3 enzyme exhibited little or no selectivity among long-chain diacylglycerols but had higher activity with more soluble substrates such as 1,2-didecanoylglycerol. Comparison of the properties of M-DG kinase with those of the bacterial membrane-bound enzyme revealed that selectivity for arachidonoyl-diacylglycerol was unique to the mammalian enzyme. All three kinases were activated by phosphatidylserine, but activation did not alter the arachidonoyl selectivity of M-DG kinase. Phosphatidylserine activated M-DG kinase by increasing Vm and decreasing the apparent Km for diacylglycerol. High concentrations of diacylglycerol reduced the Ka for phosphatidylserine, but did not abolish the phosphatidylserine requirement for maximum activity. Examination of the thermal lability of M-DG kinase revealed that this enzyme was rapidly and selectively inactivated by preincubation with its preferred substrate. This novel effect may have obscured previous attempts to discern substrate selectivity. Taken together, the results provide evidence that M-DG kinase is an arachidonoyl-diacylglycerol kinase that may participate in the formation of arachidonoyl-enriched species of phosphatidylinositol.     

Secretory IgA specific for Toxoplasma gondii

Secretory IgA specific for Toxoplasma gondii was identified in intestinal secretions of mice infected perorally with bradyzoites (encysted in brain) of the Me49 strain of T. gondii by using immunofluorescence microscopy and an ELISA. This activity was absorbed with tachyzoites of T. gondii but not mouse brain. To determine whether increased total amount of intestinal IgA might cause a nonspecific reaction in the ELISA for T. gondii-specific IgA, mice were immunized perorally with cholera toxin. This immunization produced intestinal IgA antibody to cholera toxin and increased the total amount of intestinal IgA, but there was no reactivity of intestinal secretions in the ELISA for T. gondii-specific IgA. Experiments in which ELISA were performed with monoclonal IgA, IgG, or IgM and antisera to IgA, IgG, or IgM demonstrated that the ELISA was specific for each Ig class. In addition, monoclonal IgA competed with the anti-Toxoplasma IgA activity of intestinal secretions obtained from mice infected with T. gondii.