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PubMed1998

The mouse Mid1 gene: implications for the pathogenesis of Opitz syndrome and the evolution of the mammalian pseudoautosomal region.

We have recently reported isolation of the gene responsible for X-linked Opitz G/BBB syndrome, a defect of midline development. MID1 is located on the distal short arm of the human X chromosome (Xp22. 3) and encodes a novel member of the B box family of zinc finger proteins. We have now cloned the murine homolog of MID1 and performed preliminary expression studies during development. Mid1 expression in undifferentiated cells in the central nervous, gastrointestinal and urogenital systems suggests that abnormal cell proliferation may underlie the defect in midline development characteristic of Opitz syndrome. We have also found that Mid1 is located within the mouse pseudoautosomal region (PAR) in Mus musculus , while it seems to be X-specific in Mus spretus. Therefore, Mid1 is likely to be a recent acquisition of the M. musculus PAR. Genetic and FISH analyses also demonstrated a high frequency of unequal crossovers in the murine PAR, creating spontaneous deletion/duplication events involving Mid1. These data provide evidence for the first time that genetic instability of the PAR may affect functionally important genes. In addition, we show that MID1 is the first example of a gene subject to X-inactivation in man while escaping it in mouse. These data contribute to a better understanding of the molecular content and evolution of the rodent PAR.

Abnormalities, Multiple↗
PubMed1975

A plasmid involved in chloramphenicol production in Streptomyces venezuelae: evidence from genetic mapping.

To test the hypothesis that chloramphenicol production in Streptomyces venezuelae depends on the presence of a plasmid, mapping analysis was carried out by using eight markers in addition to chloramphenicol production and melanoid pigment formation. The sequence of the eight markers was determined on a circular linkage map as follows: -his-ade-str-leu-lys-met-ilv-pro-(his-). This sequence resulted in the frequency of quadruple crossover (q.c.o.) recombinants having the lowest value, 3-2 to 4-9%. However, the character of chloramphenicol non-production, which was obtained by incubating mycelia with acriflavin, was not required to explain the results. From these results and other tests, it is concluded that chloramphenicol production is controlled by a plasmid. This plasmid appeared to be non-transferable in conjugation.

Acriflavine↗
PubMed2005

Continuous quantum measurement with independent detector cross correlations.

We investigate the advantages of using two independent, linear detectors for continuous quantum measurement. For single-shot measurement, the detection process may be quantum limited if the detectors are twins. For weak continuous measurement, cross correlations allow a violation of the Korotkov-Averin bound for the detector's signal-to-noise ratio. The joint weak measurement of noncommuting observables is also investigated, and we find the cross correlation changes sign as a function of frequency, reflecting a crossover from incoherent relaxation to coherent, out of phase oscillations. Our results are applied to a double quantum-dot charge qubit, simultaneously measured by two quantum point contacts.

Journal Article↗
PubMed2002

Sound signature for identification and quantification of upper airway disease in horses.

OBJECTIVE: To investigate whether upper airway sounds of horses exercising with laryngeal hemiplegia and alar fold paralysis have distinct sound characteristics, compared with unaffected horses. ANIMALS: 6 mature horses. PROCEDURE: Upper airway sounds were recorded in horses exercising on a high-speed treadmill at maximum heart rate (HR(MAX)) under 3 treatment conditions (ie, normal upper airway function [control condition], and after induction of left laryngeal hemiplegia or bilateral alar fold paralysis) in a randomized crossover design. Fundamental frequency, spectrograms using Gabor transform, and intensity characteristics of acquired sounds (peak sound level [sound(peak] and highest frequency of at least -25 dB sound intensity [F(25max)]) were evaluated. RESULTS: Evaluation of the fundamental frequency of the time domain signal was not useful. Sensitivity and specificity (83 and 75%, respectively) of spectrograms were greatest at maximal exercise, but the exact abnormal condition was identified in evaluation of only 12 of 18 spectrograms. Increased accuracy was obtained using sound(peak) and F(25max) as discriminating variables. The use of sound(peak) discriminated between control and laryngeal hemiplegia conditions and F(25max) between laryngeal hemiplegia and alar fold paralysis conditions. This increased the specificity of sound analysis to 92% (sensitivity 83%) and accurately classified the abnormal state in 92% of affected horses. CONCLUSIONS AND CLINICAL RELEVANCE: Sound analysis might be a useful adjunct to the diagnosis and evaluation of treatment of horses with upper airway obstruction, but would appear to require close attention to exercise intensity. Multiple measurements of recorded sounds might be needed to obtain sufficient accuracy for clinical use.

Airway Obstruction↗
PubMed1977

Relationship of lateral eye-movement to cognitive mode, hemispheric interaction, and choice of college major.

The direction and frequency of lateral eye-movements and frequency of midline crossovers, while reflecting on selected questions, are related to college major. Students in language-related fields produce larger ratios of right to left lateral movements, and fewer left movements, than do other students. Students in visual arts produce greater total numbers of movements as well as more frequent midline crossovers. Moreover, cognitive demands of questions (verbal or nonverbal) influence direction of movement most prominently in students majoring in other than art and language-related fields. Results are discussed in terms of cognitive mode, hemispheric interaction, and choice of college major.

Adult↗
PubMed1989

Aortic input impedance during hypovolemic shock and after hyperosmotic solution infusion.

Aortic input impedance (Zin) was determined in 7 chloralose-urethane-anesthetized dogs. Flow and pressure were recorded in the ascending aorta during random cardiac pacing. These signals were processed on a spectrum analyzer utilizing the Fast Fourier Transform. Measurements were made 1) under control conditions; 2) every 5 min throughout 1 hr of hypovolemic shock; 3) every 5 min for 30 min after ending infusion of hyperosmotic solution (7.5% NaCl, 4.5 ml/kg body weight). We conclude that the determination of characteristic impedance (Zc) (average value of Zin from 4 to 10 Hz) can be useful for determining the initial phase of vascular decompensation in hypovolemic shock. After hyperosmotic solution infusion we observed a reduction in peripheral resistance, Zin, Zc, frequency of minimal Zin and frequency of phase crossover. These data strongly suggest a decrease in arterial vascular tonus.

Animals↗
PubMedDate not supplied

Diltiazem dose responses in sustained therapy for stable angina pectoris.

Fifteen patients with stable effort angina were treated for 2 weeks with each of diltiazem 120 mg, 240 mg, 360 mg or placebo in a double-blind crossover protocol. The frequency of angina was decreased from 7.2 +/- 1.1 (mean +/- S.D.) episodes per 2 weeks with placebo to 5.9 +/- 5.2 (N.S.), 4.1 +/- 1.1 (p less than 0.01) and 1.5 +/- 0.8 (p less than 0.005) with 120 mg, 240 mg and 360 mg diltiazem respectively. Similar decreases occurred in nitroglycerin consumption. Ten hours after the last dose of each treatment period, each patient was challenged with 120 mg diltiazem. Treadmill exercise testing was carried out at 0, 1, 2, 4 and 8 hours. Time to onset of angina and 0.1m V ST depression increased at 1 hour, was maximal at 2 and 4 hours, and remained elevated at 8 hours. Two weeks of sustained treatment with diltiazem did not alter the responses in treadmill performance to 120 mg diltiazem. Hemodynamic changes were consistent with decreased myocardial oxygen demand and increased myocardial oxygen supply by diltiazem. There was no significant attenuation of hemodynamic response with sustained therapy. Trough plasma levels of diltiazem at 10 hours following the last dose of sustained therapy varied in a dose-dependent manner. However, corresponding exercise tolerances were identical regardless of the plasma level. Peak drug levels at 4 hours following 120 mg aldo did not correlate with exercise performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1997

Cisplatin increases meiotic crossing-over in mice.

Genetic mapping of traits and mutations in mammals is dependent upon linkage analysis. The resolution achieved by this method is related to the number of offspring that can be scored and position of crossovers near a gene. Higher precision mapping is obtained by expanding the collection of progeny from an appropriate cross, which in turn increases the number of potentially informative recombinants. A more efficient approach would be to increase the frequency of recombination, rather than the number of progeny. The anticancer drug cisplatin, which causes DNA strand breakage and is highly recombinogenic in some model organisms, was tested for its ability to induce germ-line recombination in mice. Males were exposed to cisplatin and mated at various times thereafter to monitor the number of crossovers inherited by offspring. We observed a striking increase on all three chromosomes examined and established a regimen that nearly doubled crossover frequency. The timing of the response indicated that the crossovers were induced at the early pachytene stage of meiosis I. The ability to increase recombination should facilitate genetic mapping and positional cloning in mice.

Animals↗
PubMed1998

Genetic and physical localization of the root-knot nematode resistance locus mi in tomato.

As part of a map-based cloning strategy designed to isolate the root-knot nematode resistance gene Mi, tomato F2 populations were analyzed in order to identify recombination points close to this economically important gene. A total of 21,089 F2 progeny plants were screened using morphological markers. An additional 1887 F2 were screened using PCR-based flanking markers. Fine-structure mapping of recombinants with newly developed AFLP markers, and RFLP markers derived from physically mapped cosmid subclones, localized Mi to a genomic region of about 550 kb. The low frequency of recombinants indicated that recombination was generally suppressed in these crosses and that crossovers were restricted to particular regions. To circumvent this problem, a population of Lycopersicon peruvianum, the species from which Mi was originally introgressed, that was segregating for resistance was developed. Screening of this population with PCR, RFLP and AFLP markers identified several plants with crossovers near Mi. Recombination frequency was approximately eight-fold higher in the Mi region of the L. peruvianum cross. However, even within the wild species cross, recombination sites were not uniformly distributed in the region. By combining data from the L. esculentum and L. peruvianum recombinant analyses, it was possible to localize Mi to a region of the genome spanning less than 65 kb.

Animals↗
PubMed2005

SNP microarray analysis for genome-wide detection of crossover regions.

There is a great deal of interest in understanding the non-random distribution of recombination events over the human genome, because it has important implications for using linkage disequilibrium (LD) to identify human disease genes. So far, only a few recombination hotspots in the human genome have been characterised and the identification of new crossover hotspots will contribute to a better understanding of the mechanisms that govern their formation and distribution. This study shows that high-density single nucleotide polymorphism (SNP) arrays, together with the presented analysis method, are an appropriate tool for generating a whole-genome recombination pattern and for detecting new crossover regions with enhanced recombination frequency. Based on the genotype data of 16 members of a Caucasian three-generation family, we identified 825 crossover regions. The average recombination frequency of females and males was 0.77 and 0.56 cM/Mb, respectively. We detected 24 crossover regions showing elevated recombination activity, which comprised known hotspots, like the MHC II region, confirming the non-random distribution of recombination events along the genome. Interestingly, 29.2% of the identified crossover hotspot regions overlapped with regions flanked by segmental duplications published by Bailey et al. (Science 297:1003-1007, 2002) suggesting that segmental duplications and crossover hotspot regions are mechanistically linked. By extrapolating the results of the present study, we conclude that it might be feasible, at least in part, to estimate to what extent the block-like pattern of LD exactly relies on the genome-wide crossover pattern using the next generation high-density SNP microarrays.

Crossing Over, Genetic↗
PubMed1990

Genomic replacement in Escherichia coli K-12 using covalently closed circular plasmid DNA.

A number of gene replacements at different loci were constructed using covalently closed circular (ccc) plasmid DNA in the recB21 recC22 sbcB15 sbcC201 mutant of Escherichia coli (JC7623). Selected constructs representing deletions and insertion mutations formed from double-crossover events involving the ccc plasmid molecules and the genome were confirmed by Southern blots, and the frequency of double-crossover events was evaluated. It is reported that such mutants may be constructed without linearizing plasmid DNA, as described previously.

Blotting, Southern↗
PubMedDate not supplied

Chimeric gene library construction by a simple and highly versatile method using recombination-dependent exponential amplification.

A simple and efficient method for the construction of chimeric gene libraries termed RDA-PCR (recombination-dependent exponential amplification polymerase chain reaction) was developed by modifying polymerase chain reaction. A chimeric gene library is generated from homologous parental genes with additional primer-annealing sequences at their "heads" and "tails". Two primers ("skew primers") are designed to exclusively anneal to either the heads of maternal genes or the tails of paternal genes. During the RDA-PCR, short annealing/extension periods facilitate homologous recombination. The chimeric sequences can be exponentially amplified to form the chimeric gene library, whereas parental sequences without crossovers are not amplified. As a model, we constructed a chimeric gene library of yellow and green fluorescent protein (yfp and gfp, respectively). The crossover point profile of RDA-PCR clones was compared with those obtained by (modified) family shuffling. PCR restriction fragment polymorphism (PCR-RFLP) analysis of the RDA-PCR clones showed a high content of chimeric genes in the library, whereas family shuffling required the modification using skew primers for selective enrichment of chimeric sequences. PCR-RFLP analysis also indicated that the crossover points of RDA-PCR chimeras were distributed over the entire protein-coding region. Moreover, as few as 2 bp of the continual identity of nucleotides were found at the crossover points at high frequency (30% of the tested clones), suggesting that RDA-PCR resulted in a higher diversity in crossover points than family shuffling.

Bacterial Proteins↗
PubMed2002

Electrodynamics of a Coulomb glass in n-type silicon.

Measurements of the complex frequency dependent conductivity of uncompensated n-type silicon are reported. The experiments are done in the quantum limit, variant Planck's over 2pi omega>k(B)T, across a broad doping range on the insulating side of the metal-insulator transition. The low energy linear frequency dependence is consistent with theories of a Coulomb glass, but discrepancies exist in the relative magnitudes of the complex components. At higher energies we observe a crossover to a quadratic frequency dependence that is sharper than expected. The concentration dependence gives evidence that the Coulomb interaction energy is the energy scale that determines this crossover.

Journal Article↗
PubMed1989

High-frequency oscillatory ventilation compared with conventional mechanical ventilation in the treatment of respiratory failure in preterm infants.

We conducted a multicenter randomized clinical trial to compare the efficacy and safety of high-frequency ventilation with that of conventional mechanical ventilation in the treatment of respiratory failure in preterm infants. Of 673 preterm infants weighing between 750 and 2000 g, 346 were assigned to receive conventional mechanical ventilation and 327 to receive high-frequency oscillatory ventilation. The incidence of bronchopulmonary dysplasia was similar in the two groups (high-frequency ventilation, 40 percent; conventional mechanical ventilation, 41 percent; P = 0.79). High-frequency ventilation did not reduce mortality (18 percent, vs. 17 percent with conventional ventilation; P = 0.73) or the level of ventilatory support during the first 28 days. The crossover rate from high-frequency ventilation to conventional mechanical ventilation was greater than the crossover rate from mechanical to high-frequency ventilation (26 vs. 17 percent; P = 0.01). High-frequency ventilation, as compared with conventional mechanical ventilation, was associated with an increased incidence of pneumoperitoneum of pulmonary origin (3 vs. 1 percent; P = 0.05), grades 3 and 4 intracranial hemorrhage (26 vs. 18 percent; P = 0.02), and periventricular leukomalacia (12 vs. 7 percent; P = 0.05). These results suggest that high-frequency oscillatory ventilation, as used in this trial, does not offer any advantage over conventional mechanical ventilation in the treatment of respiratory failure in preterm infants, and it may be associated with undesirable side effects.

Bronchopulmonary Dysplasia↗
PubMed2001

Hierarchy of spatial interactions in the processing of contrast-defined contours.

Both psychophysical and neurophysiological evidence suggest that there are two visual cortical processing streams, a linear stream that processes first-order stimuli and a nonlinear stream that also processes second-order stimuli. This evidence also suggests that before the extraction of the second-order signal, the nonlinear pathway broadly but not completely pools signals across initial linear filters that encode the orientation of the carrier of the second-order signal. The evidence suggests that such pooling does not occur across carrier spatial frequencies. We show that similar results are obtained with repulsion tilt illusions but not with attraction effects. Attraction effects exhibit complete orientation crossover (while retaining spatial frequency selectivity), perhaps indicating higher-level processing; an experiment on interocular transfer of the effects supported this conclusion.

Contrast Sensitivity↗
PubMed1982

Alpha-thalassemia in two Mediterranean populations.

We used restriction endonuclease analysis to determine the incidence of alpha-thalassemia in two Mediterranean islands. In a random population sample, the gene frequency of deletion-type alpha-thalassemia-2 (-alpha) was 0.18 in Sardinians and 0.07 in Greek Cypriots. All cases were the rightward crossover type. From these frequencies and the known incidence of hemoglobin-H disease in these populations, we calculated the frequency of the alpha-thalassemia-1 genotype (--) and determined that it was low. We also found that beta-thalassemia homozygotes in sardinia have a higher incidence of alpha-thalassemia than normals and beta thalassemia heterozygotes because a significantly greater number of these homozygotes are also homozygous for the alpha-thalassemia-2 lesion. These findings support the theory that coinheritance of alpha-thalassemia mitigates the severity of beta-thalassemia and suggest that the protection is most pronounced when two alpha-globin genes are deleted.

Cyprus↗
PubMed2005

Estimation of gametic frequencies from F2 populations using the EM algorithm and its application in the analysis of crossover interference in rice.

The gametes produced in meiosis provide information on the frequency of recombination and also on the interdependence of recombination events, i.e. interference. Using F(2) individuals, it is not possible in all cases to derive the gametes, which have fused, and which provide the information about interference unequivocally when three or more segregating markers are considered simultaneously. Therefore, a method was developed to estimate the gametic frequencies using a maximum likelihood approach together with the expectation maximisation algorithm. This estimation procedure was applied to F(2) mapping data from rice (Oryza sativa L.) to carry out a genome-wide analysis of crossover interference. The distribution of the coefficient of coincidence in dependence on the recombination fraction revealed for all chromosomes increasing positive interference with decreasing interval size. For some chromosomes this mutual inhibition of recombination was not so strong in small intervals. The centromere had a significant effect on interference. The positive interference found in the chromosome arms were reduced significantly when the intervals considered spanned the centromere. Two chromosomes even demonstrated independent recombination and slightly negative interference for small intervals including the centromere. Different marker densities had no effect on the results. In general, interference depended on the frequency of recombination events in relation to the physical length. The strength of the centromere effect on interference seemed to depend on the strength of recombination suppression around the centromere.

Centromere↗
PubMed2006

Temporal analysis of meiotic DNA double-strand break formation and repair in Drosophila females.

Using an antibody against the phosphorylated form of His2Av (gamma-His2Av), we have described the time course for the series of events leading from the formation of a double-strand break (DSB) to a crossover in Drosophila female meiotic prophase. MEI-P22 is required for DSB formation and localizes to chromosomes prior to gamma-His2Av foci. Drosophila females, however, are among the group of organisms where synaptonemal complex (SC) formation is not dependent on DSBs. In the absence of two SC proteins, C(3)G and C(2)M, the number of DSBs in oocytes is significantly reduced. This is consistent with the appearance of SC protein staining prior to gamma-His2Av foci. However, SC formation is incomplete or absent in the neighboring nurse cells, and gamma-His2Av foci appear with the same kinetics as in oocytes and do not depend on SC proteins. Thus, competence for DSB formation in nurse cells occurs with a specific timing that is independent of the SC, whereas in the oocytes, some SC proteins may have a regulatory role to counteract the effects of a negative regulator of DSB formation. The SC is not sufficient for DSB formation, however, since DSBs were absent from the heterochromatin even though SC formation occurs in these regions. All gamma-His2Av foci disappear before the end of prophase, presumably as repair is completed and crossovers are formed. However, oocytes in early prophase exhibit a slower response to X-ray-induced DSBs compared to those in the late pachytene stage. Assuming all DSBs appear as gamma-His2Av foci, there is at least a 3:1 ratio of noncrossover to crossover products. From a comparison of the frequency of gamma-His2Av foci and crossovers, it appears that Drosophila females have only a weak mechanism to ensure a crossover in the presence of a low number of DSBs.

Animals↗