A genomewide exploration suggests a new candidate gene at chromosome 11q23 as the major determinant of plasma homocysteine levels: results from the GAIT project

Homocysteine (Hcy) plasma level is an independent risk marker for venous thrombosis, myocardial infarction, stroke, congestive heart failure, osteoporotic fractures, and Alzheimer disease. Hcy levels are determined by the interaction of genetic and environmental factors. The genetic basis is still poorly understood, since only the MTHFR 677 C-->T polymorphism has been consistently associated with plasma Hcy levels. We conducted a genomewide linkage scan for genes affecting variation in plasma Hcy levels in 398 subjects from 21 extended Spanish families. A variance-components linkage method was used to analyze the data. The strongest linkage signal (LOD score of 3.01; genomewide P = .035) was found on chromosome 11q23, near marker D11S908, where a candidate gene involved in the metabolism of Hcy (the nicotinamide N-methyltransferase gene [NNMT]) is mapped. Haplotype analyses of 10 single-nucleotide polymorphisms within this gene found one haplotype associated with plasma Hcy levels (P = .0003). Our results, to our knowledge, represent the first genomic scan for quantitative variation in Hcy plasma levels. They strongly suggest that the NNMT gene could be a major genetic determinant of plasma Hcy levels in Spanish families. Since this gene encodes an enzyme involved in Hcy synthesis, this finding would be consistent with known biochemical pathways. These data could be relevant in determining the relationships between Hcy level, cardiovascular disease, osteoporosis, and Alzheimer disease.     

In vitro bypass of malondialdehyde-deoxyguanosine adducts: differential base selection during extension by the Klenow fragment of DNA polymerase I is the critical determinant of replication outcome

The major malondialdehyde-derived adduct in DNA is 3-(2'-deoxy-beta-D-erythro-pentofuranosyl)pyrimido[1,2-alpha]purin-10(3H)-one (M(1)dG). M(1)dG undergoes hydrolytic ring opening in duplex DNA to 9-(2'-deoxy-beta-D-erythro-pentofuranosyl)-N(2)-(3-oxo-1-propenyl)guanine (N(2)OPdG). Template-primers were constructed containing M(1)dG or N(2)OPdG in a (CpG)(4) repeat sequence and replicated with the Klenow fragment of DNA polymerase I (Kf). Incorporation opposite the lesion and replication beyond the adduct sites by Kf was reduced compared to unadducted controls. The amount of bypass to full-length products was significantly greater with the acyclic adduct, N(2)OPdG, than with the cyclic adduct, M(1)dG. Sequence analysis indicated that the fully extended primers contained dC opposite both adducts when replication was conducted with Kf exo(+). In contrast, with Kf exo(-), primers extended past M(1)dG contained T opposite the adduct, but primers extended past N(2)OPdG contained dC opposite the adduct. Single nucleotide incorporation experiments indicated that Kf exo(-) incorporates all four nucleotides opposite M(1)dG or N(2)OPdG. Kf exo(+) removed dA, dG, and T opposite M(1)dG and N(2)OPdG but was much less active when dC was opposite the adduct. NMR studies on duplex DNA indicated that N(2)OPdG hydrogen bonds with dC in the complementary strand. The fact that base pairing can occur for the acyclic adduct may explain why N(2)OPdG is less blocking than M(1)dG. These results support in vivo findings that the ring-closed adduct, M(1)dG, is more mutagenic than the ring-opened adduct, N(2)OPdG. They also provide a detailed picture of in vitro replication in which the outcome is determined primarily by the selectivity of template-primer extension beyond rather than insertion opposite the adducts.     

Pheromone-induced polarization is dependent on the Fus3p MAPK acting through the formin Bni1p

During mating, budding yeast cells reorient growth toward the highest concentration of pheromone. Bni1p, a formin homologue, is required for this polarized growth by facilitating cortical actin cable assembly. Fus3p, a pheromone-activated MAP kinase, is required for pheromone signaling and cell fusion. We show that Fus3p phosphorylates Bni1p in vitro, and phosphorylation of Bni1p in vivo during the pheromone response is dependent on Fus3p. fus3 mutants exhibited multiple phenotypes similar to bni1 mutants, including defects in actin and cell polarization, as well as Kar9p and cytoplasmic microtubule localization. Disruption of the interaction between Fus3p and the receptor-associated Galpha subunit caused similar mutant phenotypes. After pheromone treatment, Bni1p-GFP and Spa2p failed to localize to the cortex of fus3 mutants, and cell wall growth became completely unpolarized. Bni1p overexpression suppressed the actin assembly, cell polarization, and cell fusion defects. These data suggest a model wherein activated Fus3p is recruited back to the cortex, where it activates Bni1p to promote polarization and cell fusion.     

The effects of interaction compartments on stability for competitive systems

The interactions between species are unlikely to be randomly arranged, and there is increasing evidence that most interactions occur within small species sub-groups, or compartments, that do not strongly interact with one another. We examine whether arranging the interactions of a competitive system into compartments influences the system properties of linear stability, feasibility, reactivity, and biomass stability, thereby altering the likelihood of species persistence. Model Lotka-Volterra systems of diffuse competition were analysed with interactions arranged randomly and in compartments. It was found, using a variety of dynamical measures, that arranging interactions into compartments enhances the likelihood of species persistence. Since many natural competitive systems appear to have interactions arranged within compartments, this may be an outcome of the positive attributes that this form of organization offers.     

Lipopenia and skin barrier abnormalities in DGAT2-deficient mice

The synthesis of triglycerides is catalyzed by two known acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes. Although they catalyze the same biochemical reaction, these enzymes share no sequence homology, and their relative functions are poorly understood. Gene knockout studies in mice have revealed that DGAT1 contributes to triglyceride synthesis in tissues and plays an important role in regulating energy metabolism but is not essential for life. Here we show that DGAT2 plays a fundamental role in mammalian triglyceride synthesis and is required for survival. DGAT2-deficient (Dgat2(-/-)) mice are lipopenic and die soon after birth, apparently from profound reductions in substrates for energy metabolism and from impaired permeability barrier function in the skin. DGAT1 was unable to compensate for the absence of DGAT2, supporting the hypothesis that the two enzymes play fundamentally different roles in mammalian triglyceride metabolism.     

Evidence for sex-specific risk alleles in autism spectrum disorder

We investigated the genetic aspects of the large sex bias in the prevalence of autism spectrum disorder by monitoring changes in linkage when the family set for an affected sibling pair genome scan is subdivided on the basis of the sex of affected children. This produces a significant excess in the total number of linkage peaks (P=1.3 x 10(-8)) and identifies a major male-specific linkage peak at chromosome 17q11 (P<.01). These results suggest that sexual dichotomy is an important factor in the genetics of autism; the same strategy can be used to explore this possibility in other complex disorders that exhibit significant sex biases.     

Indiscriminate polyandry and male parental effort

Extrapair paternity involves cooperation between mated females and extrapair males. On the other hand, mated males exhibit a spectrum of anti-cuckolding strategies. Hence, extrapair attributes of diverse species and populations reported in the literature are particular solutions of evolutionary games involving gender-specific cuckolding/anti-cuckolding strategies. Here we use game theoretical methods to study the effect of male paternal effort conserving strategies in situations where females seek extrapair fertilizations (EPF) for reasons of genetic compatibility and/or in pursuit of genetic diversity for their offspring. In such cases, females cannot make a pre-copulatory selection of the optimal genetic partners, and therefore combine promiscuous copulation with the use of in copula and/or post-copulatory selection mechanisms to optimize the genetic endowment of their offspring—indiscriminate polyandry. Our results indicate that, when indiscriminate polygamy is constrained by the availability of extrapair male partners, there are three possible (parameter regime wise) evolutionary stable strategy solutions. (1) All females seek EPF, while all males restrict parental care. (2) All females seek EPF, while all males are unconditionally parental. (3) Females use a combination strategy where pursuit of EPF is mixed—on either a population, or an individual level—with genetic monogamy, while all males use a conditional paternal care strategy, which involves adjusting their parental efforts according to their certainty of paternity.     

Tryptophan metabolism and oxidative stress in patients with Huntington's disease

Abnormalities in the kynurenine pathway may play a role in Huntington's disease (HD). In this study, tryptophan depletion and loading were used to investigate changes in blood kynurenine pathway metabolites, as well as markers of inflammation and oxidative stress in HD patients and healthy controls. Results showed that the kynurenine : tryptophan ratio was greater in HD than controls in the baseline state and after tryptophan depletion, indicating increased indoleamine dioxygenase activity in HD. Evidence for persistent inflammation in HD was provided by elevated baseline levels of C-reactive protein, neopterin and lipid peroxidation products compared with controls. The kynurenate : kynurenine ratio suggested lower kynurenine aminotransferase activity in patients and the higher levels of kynurenine in patients at baseline, after depletion and loading, do not result in any differences in kynurenic acid levels, providing no supportive evidence for a compensatory neuroprotective role for kynurenic acid. Quinolinic acid showed wide variations in blood levels. The lipid peroxidation data indicate a high level of oxidative stress in HD patients many years after disease onset. Levels of the free radical generators 3-hydroxykynurenine and 3-hydroxyanthranilic acid were decreased in HD patients, and hence did not appear to contribute to the oxidative stress. It is concluded that patients with HD exhibit abnormal handling of tryptophan metabolism and increased oxidative stress, and that these factors could contribute to ongoing brain dysfunction.     

VCAM-1 expression on CD8+ cells correlates with enhanced anti-HIV suppressing activity

CD8(+) cells from HIV-infected individuals showing the CD8(+) cell noncytotoxic antiviral response unexpectedly revealed mRNA for VCAM-1, a cell surface molecule found on endothelial cells. Uninfected subjects had undetectable levels of VCAM-1 mRNA in their CD8(+) cells. Flow cytometry analysis showed that up to 12% of the CD8(+) cells from HIV-positive individuals expressed VCAM-1 compared with 0.8% of the CD8(+) cells of HIV-negative individuals. Enrichment of the CD8(+)VCAM-1(+) cell population and subsequent coculture with CD4(+) cells acutely infected with HIV-1 showed that the VCAM-1(+)CD8(+) cells were able to suppress viral replication with 50% less input cells than the unseparated CD8(+) cell population. This study demonstrates, for the first time, the expression of VCAM-1 on CD8(+) cells. Moreover, the CD8(+)VCAM-1(+) cells show enhanced CD8(+) cell noncytotoxic antiviral response activity that could have clinical importance in HIV infection.     

Design, synthesis and structure-activity relationships of 6-O-arylpropargyl diazalides with potent activity against multidrug-resistant Streptococcus pneumoniae

A novel series of 6-O-arylpropargyl diazalides was synthesized and evaluated for their antibacterial activity. Members of this series exhibited potent activity against erythromycin-resistant respiratory tract pathogens.