Biomedical subjects

E Nevo

Publications and source records attributed to E Nevo.

At least 73 records · Page 4Linked to original sources

PubMed2000

Ecologic genomics of DNA: upstream bending in prokaryotic promoters.

After our analysis of the distribution of predicted intrinsic curvature along all available complete prokaryotic genomes, the genomes were divided into two groups. Curvature distribution in all prokaryotes of the first group indicated a substantial fraction of promoters characterized by intrinsic DNA curvature located within or upstream of the promoter region. We did not find this peculiar DNA curvature distribution in prokaryotes in the second group. Remarkably, all bacteria of the first group were mesophilic, whereas many prokaryotes of the second group were hyperthermophilic. We hypothesize that DNA curvature plays a biologic role in gene regulation in mesophilic as opposed to hyperthermophilic prokaryotes, i.e., DNA curvature presumably has a functional adaptive significance determined by temperature selection.

5' Untranslated Regions↗

PubMed2000

Molecular genetic maps in wild emmer wheat, Triticum dicoccoides: genome-wide coverage, massive negative interference, and putative quasi-linkage.

The main objectives of the study reported here were to construct a molecular map of wild emmer wheat, Triticum dicoccoides, to characterize the marker-related anatomy of the genome, and to evaluate segregation and recombination patterns upon crossing T. dicoccoides with its domesticated descendant Triticum durum (cultivar Langdon). The total map length exceeded 3000 cM and possibly covered the entire tetraploid genome (AABB). Clusters of molecular markers were observed on most of the 14 chromosomes. AFLP (amplified fragment length polymorphism) markers manifested a random distribution among homologous groups, but not among genomes and chromosomes. Genetic differentiation between T. dicoccoides and T. durum was attributed mainly to the B genome as revealed by AFLP markers. The segregation-distorted markers were mainly clustered on 4A, 5A, and 5B chromosomes. Homeoalleles, differentially conferring the vigor of gametes, might be responsible for the distortion on 5A and 5B chromosomes. Quasilinkage, deviation from free recombination between markers of nonhomologous chromosomes, was discovered. Massive negative interference was observed in most of the chromosomes (an excess of double crossovers in adjacent intervals relative to the expected rates on the assumption of no interference). The general pattern of distribution of islands of negative interference included near-centromeric location, spanning the centromere, and median/subterminal location. [An appendix describing the molecular marker loci is available as an online supplement at http://www.genome.org.]

Binomial Distribution↗

PubMed2000

Extraordinary multilocus genetic organization in mole crickets, Gryllotalpidae.

Allozymic diversity at 21 loci was analyzed in 470 individuals of three species of mole cricket superspecies, Gryllotalpa gryllotalpa (two new chromosomal species, G. tali and G. marismortui) and G. africana in Israel, which are distributed along a southward transect of increasing aridity. Two outstanding findings emerged in G. tali and G. marismortui: (1) genetic polymorphism was high but heterozygosity very low, indicating significant deviations from Hardy-Weinberg expectations; and (2) significant linkage disequilibria at an unprecedented level for outbreeders and remarkable intersite differences. The results may characterize subterranean gryllotalpids worldwide because a single sample of Neocurtilla hexadactyla from Tefé, Amazonia, shows the same features. Significant variation of heterozygote paucity among loci, combined with the biology of the species, rejects the simple explanation of inbreeding or any other single explanatory model. Likewise, direct selection against heterozygotes or specific multilocus associations can explain, but is not necessary nor likely to explain, the observed results in mole crickets. To explain these results, we developed a multiple-factor mathematical model combining niche viability selection, niche choice, and positive assortative mating. This model involves a special case of Wahlund effect and inbreeding. Simulations based on this model showed that a combination of these three mechanisms may produce the observed distribution of alleles, via selection on a few loci, to affect the entire genome organization.

Animals↗

PubMed2000

Coevolution of A and B genomes in allotetraploid Triticum dicoccoides.

Data is presented on the coevolution of A and B genomes in allotetraploid wheat Triticum dicoccoides (2n = 4x = 28, genome AABB) obtained by genomic in situ hybridization (GISH). Probing chromosomes of T. dicoccoides with DNA from the proposed A/B diploid genome ancestors shows evidence of enriching A-genome with repetitive sequences of B-genome type. Thus, ancestral S-genome sequences have spread throughout the AB polyploid genome to a greater extent than have ancestral A-genome sequences. The substitution of part of the A-genome heterochromatin clusters by satellite DNA of the B genome is detected by using the molecular banding technique. The cause may be interlocus concerted evolution and (or) colonization. We propose that the detected high level of intergenomic invasion in old polyploids might reflect general tendencies in speciation and stabilization of the allopolyploid genome.

Chromosome Mapping↗

PubMed1999

Spectral tuning of a circadian photopigment in a subterranean 'blind' mammal (Spalax ehrenbergi).

The atrophied subcutaneous eyes of Spalax ehrenbergi (the blind mole rat) express a long wavelength sensitive (LWS) cone opsin. Our data provide strong evidence that this photopigment is spectrally tuned to enhance photon capture in the red light environment of the eye. Furthermore, novel mechanisms appear partially responsible for this sensory fine-tuning. These data support the hypothesis that the LWS opsin of Spalax acts as a functional photopigment and that it is not a 'residue' of the pre-subterranean visual system. As the eye of Spalax has only one known function, the entrainment of circadian rhythms to environmental light, the LWS photopigment is implicated in this task. These results, together with our recent findings that rod and cone photopigments are not required for murine photoentrainment, suggest that multiple photopigments (classical and novel) mediate the effects of light on the mammalian circadian system.

Amino Acid Sequence↗

PubMed1999

Adaptive hypoxic tolerance in the subterranean mole rat Spalax ehrenbergi: the role of vascular endothelial growth factor.

Spalax ehrenbergi has evolved adaptations that allow it to survive and carry out normal activities in a highly hypoxic environment. A key component of this adaptation is a higher capillary density in some Spalax tissues resulting in a shorter diffusion distance for oxygen. Vascular endothelial growth factor (VEGF) is an angiogenic factor that is critical for angiogenesis during development and in response to tissue ischemia. We demonstrate here that VEGF expression is markedly increased in those Spalax tissues with a higher capillary density relative to the normal laboratory rat Rattus norvegicus. Upregulation of VEGF thus appears to be an additional mechanism by which Spalax has adapted to its hypoxic environment.

Acclimatization↗

PubMed1999

Abundant multilocus polymorphisms caused by genetic interaction between species on trait-for-trait basis.

This paper deals with the problem of polymorphism maintenance in species coevolution mediated by selection for quantitative traits controlled by Mendelian genes. We showed here that the conditions for polymorphism maintenance in interacting species can be deduced from the behavior of the isolated partners in stable and changing environments. This allows also to address such difficult questions as evolution of sex and recombination, that can not be considered properly in non-Mendelian models. An abundance of polymorphic regimes was revealed in the proposed genetic model. The obtained results demonstrate a remarkable property of trait-dependent coevolution concerning the conditions for maintenance of genetic polymorphism: what seems to be more realistic, that is, non-equal gene effects and deviation from purely additive within-locus gene action, promotes polymorphism.

Animals↗

PubMed1999

Improved left ventricular mechanics from acute VDD pacing in patients with dilated cardiomyopathy and ventricular conduction delay.

BACKGROUND: Ventricular pacing can improve hemodynamics in heart failure patients, but direct effects on left ventricular (LV) function from varying pacing site and atrioventricular (AV) delay remain unknown. We hypothesized that the magnitude and location of basal intraventricular conduction delay critically influences pacing responses and that single-site pacing in the delay-activated region yields similar or better responses to biventricular pacing. METHODS AND RESULTS: Aortic and LV pressures were measured in 18 heart failure patients (mean+/-SD: LV ejection fraction, 19+/-7%; LV end-diastolic pressure, 25+/-8 mm Hg; QRS duration, 157+/-36 ms). Data under normal sinus rhythm were compared with ventricular pacing (VDD) at varying sites and AV delays (randomized order). Right ventricular (RV) apical or midseptal pacing had negligible contractile/systolic effects. However, LV free-wall pacing raised dP/dtmax by 23.7+/-19.0% and pulse-pressure by 18.0+/-18.4% (P<0.01). Biventricular pacing yielded less change (+12.8+/-9.3% in dP/dtmax, P<0.05 versus LV). Pressure-volume analysis performed in 11 patients consistently revealed minimal changes with RV pacing but increased stroke work and lower end-systolic volumes with LV pacing. Optimal AV intervals averaged 125+/-49 ms, and within this range, AV delay had less influence on LV function than pacing site. Basal QRS duration positively correlated with %DeltadP/dtmax (P<0.005), but pacing efficacy was not associated with QRS narrowing. Conduction delay pattern generally predicted pacing sites with most effect. CONCLUSIONS: VDD pacing acutely enhances contractile function in heart failure patients with intraventricular conduction delay. Single-site pacing at the site of greatest delay achieves similar or greater benefits to biventricular pacing in such patients. These data clarify pacing-effect mechanisms and should help in candidate identification for future studies.

Adult↗

PubMed1999

Molecular evolution of cytochrome b of subterranean mole rats, Spalax ehrenbergi superspecies, in Israel.

We describe the molecular evolution of cytochrome b of blind subterranean mole rats. We examined 12 individuals for nucleotide differences in the region of 402 base pairs of mitochondrial cytochrome b. Each individual represents a different population from the entire ecological and speciational range of the four chromosomal species in Israel (2n = 52, 54, 58, and 60) belonging to the Spalax ehrenbergi superspecies. Our results indicate the following. (i) There are seven first-position transitional differences, compared to 34 variable third positions, with no observed second-position substitutions. (ii) A maximum of four amino acids differences occurs across the range. (iii) Within-species diversity increases southward. Only 1 autoapomorphic substitution characterizes either 2n = 52 or 2n = 54, but 6-11 substitutions characterize 2n = 58, and 9-13 substitutions characterize 2n = 60. (iv) Both parsimony and maximum-likelihood trees suggest two monophyletic groups: (a) 2n = 52 and 54, and (b) 2n = 58 and 60, as identified earlier by other protein and DNA markers. (v) Mitochondrial cytochrome b heterogeneity is significantly correlated with climatic factors (rainfall) and biotic factors (body size and allozymes). We hypothesize that two selective regimes direct cytochrome b evolution in the S. ehrenbergi superspecies: (i) purifying selection in the flooded, mesic, hypoxic northern range of 2n = 52 and 54 and (ii) diversifying selection in the climatically spatiotemporal, xeric, and variable southern range of 2n = 58 and 60. Thus, the molecular evolution of mitochondrial cytochrome b in S. ehrenbergi is explicable by opposite selective stresses across the range of S. ehrenbergi in Israel, associated with the ecological adaptive radiation of the complex.

Amino Acids↗

PubMed1999

Verapamil acutely reduces ventricular-vascular stiffening and improves aerobic exercise performance in elderly individuals.

OBJECTIVES: We tested the hypothesis that acute intravenous verapamil acutely enhances aerobic exercise performance in healthy older individuals in association with a combined reduction of ventricular systolic and arterial vascular stiffnesses. BACKGROUND: Age-related vascular stiffening coupled with systolic ventricular stiffening may limit cardiovascular reserve and, thus, exercise performance in aged individuals. METHODS: Nineteen healthy volunteers with mean age 70 +/- 10 years underwent maximal-effort upright ergometry tests on two separate days after receiving either 0.15 mg/kg i.v. verapamil or 0.5 N saline in a double-blind, randomized, crossover study. RESULTS: Baseline vascular stiffness, indexed by arterial pulse-wave velocity (Doppler) and augmentation index (carotid tonometry) declined with verapamil (-5.9 +/- 2.1% and -31.7 +/- 12.8%, respectively, both p < 0.05). Preload-adjusted maximal ventricular power, a surrogate for ventricular end-systolic stiffness, also declined by -9.5 +/- 3.6%. Peripheral resistance and peak filling rate were unchanged. With verapamil, exercise duration prior to the anaerobic threshold (AT) increased by nearly 50% (260 +/- 129 to 387 +/- 176 s) with a corresponding 13.4 +/- 4.7% rise in oxygen consumption (VO2) at that time (both p < 0.01). Total exercise duration prolonged by +6 +/- 2.7% (p < 0.05) with no change in maximal VO2. Baseline cardiodepression from verapamil reversed by peak exercise with net increases in stroke volume and cardiac output (p < 0.05). CONCLUSIONS: Acute intravenous verapamil reduces ventriculovascular stiffening and improves aerobic exercise performance in healthy aged individuals. This highlights a role for heart-arterial coupling in modulating exertional capacity in the elderly, suggesting a potentially therapeutic target for aged individuals with exertional limitations.

Aged↗

PubMed1999

RAPD divergence caused by microsite edaphic selection in wild barley.

Random amplified polymorphic DNA polymerase chain reaction (RAPDPCR) was used to assess genetic diversity in four subpopulations (86 individuals) of wild barley, Hordeum spontaneum, sampled from Tabigha microsite near the Sea of Galilee, Israel. The microsite consists of two 100 m transects that are topographically separated by 100 m, each equally subdivided into 50 M of basalt and terra rossa soil types. Despite the same macroclimate characterizing the area around the Sea of Galilee, the microsite offers two edaphically different microhabitats, with basalt being a more ecologically heterogeneous and broaderniche than the relatively drier but more homogeneous and narrowniche terra rossa. Analysis of 118 putative loci revealed significant (P<0.05) genetic differentiation in polymorphism (P0.05) between the two soils across the transects with P being higher in the more heterogeneous basalt (mean P0.05 = 0.902), than in terra rossa (mean P0.05 = 0.820). Gene diversity (He) was higher in basalt (mean He=0.371), than in terra rossa (mean He=0.259). Furthermore, unique alleles were confined to one soil type, either in one or both transects. Rare alleles were observed more frequently in terra rossa than basalt, and in transect II only. Gametic phase disequilibria showed a larger multilocus association of alleles in basalt than terra rossa, and in transect I than II. Spearman rank correlation (r(s)) revealed a strong association between specific loci and soil types, and transects. Also, analysis of multilocus organization revealed soilspecific multilocusgenotypes. Therefore, our results suggest an edaphically differentiated genetic structure, which corroborates the niche widthvariation hypothesis, and can be explained, in part, by natural selection. This pattern of RAPD diversity is in agreement with allozyme and hordein protein diversities in the same subpopulations studied previously.

Journal Article↗

PubMed1999

Single- and multiple-trait mapping analysis of linked quantitative trait loci. Some asymptotic analytical approximations.

Estimating the resolution power of mapping analysis of linked quantitative trait loci (QTL) remains a difficult problem, which has been previously addressed mainly by Monte Carlo simulations. The analytical method of evaluation of the expected LOD developed in this article spreads the "deterministic sampling" approach for the case of two linked QTL for single- and two-trait analysis. Several complicated questions are addressed through this evaluation: the dependence of QTL detection power on the QTL effects, residual correlation between the traits, and the effect of epistatic interaction between the QTL for one or both traits on expected LOD (ELOD), etc. Although this method gives only an asymptotic estimation of ELOD, it allows one to get an approximate assessment of a broad spectrum of mapping situations. A good correspondence was found between the ELODs predicted by the model and LOD values averaged over Monte Carlo simulations.

Chromosome Mapping↗

PubMed1999

Retrotransposon BARE-1 and Its Role in Genome Evolution in the Genus Hordeum.

The replicative retrotransposon life cycle offers the potential for explosive increases in copy number and consequent inflation of genome size. The BARE-1 retrotransposon family of barley is conserved, disperse, and transcriptionally active. To assess the role of BARE-1 in genome evolution, we determined the copy number of its integrase, its reverse transcriptase, and its long terminal repeat (LTR) domains throughout the genus Hordeum. On average, BARE-1 contributes 13.7 x 10(3) full-length copies, amounting to 2.9% of the genome. The number increases with genome size. Two LTRs are associated with each internal domain in intact retrotransposons, but surprisingly, BARE-1 LTRs were considerably more prevalent than would be expected from the numbers of intact elements. The excess in LTRs increases as both genome size and BARE-1 genomic fraction decrease. Intrachromosomal homologous recombination between LTRs could explain the excess, removing BARE-1 elements and leaving behind solo LTRs, thereby reducing the complement of functional retrotransposons in the genome and providing at least a partial "return ticket from genomic obesity."

Journal Article↗

PubMed1999

Parametric model derivation of transfer function for noninvasive estimation of aortic pressure by radial tonometry.

Aortic pressure can be estimated noninvasively by applying a transfer function (TF) to radial tonometry signals. This study compares the performance of prior approaches, based on Fourier transform and inverted aortic-to-radial model, with direct radial-to-aortic autoregressive exogenous (ARX) model. Simultaneous invasive aortic pressure and radial tonometry pressure were recorded during rest in 39 patients in the supine position. Individual radial-aortic TF's were estimated from 20 patients, and the average TF was used to predict aortic pressures in the remaining 19 patients. The direct average TF yielded accurate aortic systolic pressure estimation (error 0.4 +/- 2.9 mmHg) and good reproduction of the aortic pressure waveform (root mean squared error 2.2 +/- 0.9 mmHg). The inverted reverse TF (aortic radial) yielded comparable results, while the Fourier-based TF had worse performance. Individual direct TF provided improved predictive accuracy only for indexes which are based on higher frequency components of the waveform (augmentation index, systolic time period). An ARX average TF can be used to accurately estimate central aortic pressure waveform parameters from noninvasive radial pulse tracings, and its performance is superior to previous techniques.

Adult↗

PubMed1999

Isolation of microsatellite and RAPD markers flanking the Yr15 gene of wheat using NILs and bulked segregant analysis.

Microsatellite and random amplified polymorphic DNA (RAPD) primers were used to identify molecular markers linked to the Yr15 gene which confer resistance to stripe rust (Puccina striiformis Westend) in wheat. By using near isogenic lines (NILs) for the Yr15 gene and a F2 mapping population derived from crosses of these lines and phenotyped for resistance, we identified one microsatellite marker (GWM33) and one RAPD marker (OPA19(800)) linked to Yr15. Then, bulked segregant analysis was used in addition to the NILs to identify RAPD markers linked to the target gene. Using this approach, two RAPD markers linked to Yr15 were identified, one in coupling (UBC199(700)) and one in repulsion phase (UBC212(1200)). After MAPMAKER linkage analysis on the F2 population, the two closest markers were shown to be linked to Yr15 within a distance of about 12 cM. The recombination rates were recalculated using the maximum likelihood technique to take into account putative escaped individuals from the stripe rust resistance test and obtain unbiased distance estimates. As a result of this study, the stripe rust resistance gene Yr15 is surrounded by two flanking PCR markers, UBC199(700) and GWM33, at about 5 cM from each side.

Chromosome Mapping↗

PubMed1999

Genome size variation in Hordeum spontaneum populations

Populations of wild barley, Hordeum spontaneum (C. Koch), originating from 10 ecologically and geographically different sites in Israel, were assessed for genome size. Measurements were obtained by flow cytometry using propidium iodide staining. Genome sizes ranged from 9.35 to 9.81 pg. Variance analysis indicated a significant difference between populations. Genome sizes were positively correlated with mean January temperature. Our results corroborate previous findings of intraspecific variation in genome size from different plant species. The positive correlations between climate and genome size suggest that the latter is adaptive and determined by natural selection.

Journal Article↗

PubMed1999

Cloning and characterisation of the gene encoding mole rat (Spalax ehrenbergi) growth hormone.

In mammals the structure of pituitary GH is generally strongly conserved, reflecting a slow basal rate of molecular evolution. However, on a few occasions the rate has increased - markedly during the evolution of primates and artiodactyls, and to a small extent during the evolution of rodents and rabbit - giving rise to marked differences between GH sequences of these species. In order to extend knowledge of rodent GHs we have cloned and characterised part of the GH gene of the Eurasian mole rat (Spalax ehrenbergi) using genomic DNA and a PCR technique. The sequence of all of the coding region and 5' untranslated region (UTR), most of the 3' UTR and part of the promoter region is described. The overall organisation of the mole rat GH gene is similar to that of GH genes from other mammals. The proximal Pit-1 sequence in the gene promoter differs somewhat from that of rat or mouse. The deduced sequence for the mature GH from mole rat differs from that of pig GH (thought to be identical to the ancestral placental mammal GH sequence) at 7 residues and from rat, mouse and hamster GHs at 9 to 12 residues. Only one or two of these substitutions involve residues close to the receptor-binding sites of the hormone.

Amino Acid Sequence↗

PubMed1998

Fungal life in the extremely hypersaline water of the Dead Sea: first records.

The first report, to our knowledge, on the occurrence of filamentous fungi in the hypersaline (340 g salt l-1) Dead Sea is presented. Three species of filamentous fungi from surface water samples of the Dead Sea were isolated: Gymnascella marismortui (Ascomycota), which is described as a new species, Ulocladium chlamydosporum and Penicillium westlingii (Deuteromycota). G. marismortui and U. chlamydosporum grew on media containing up to 50% Dead Sea water. G. marismortui was found to be an obligate halophile growing optimally in the presence of 0.5-2 M NaCl or 10 30% (by volume) of Dead Sea water. Isolated cultures did not grow on agar media without salt, but grew on agar prepared with up to 50% Dead Sea water. This suggests that they may be adapted to life in the extremely stressful hypersaline Dead Sea.

Fungi↗