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PubMed2002

Alternate site glucose testing: a crossover design.

A crossover design study was conducted to determine if reducing pain, by using alternative sites off the finger tip, would increase testing frequency and improve clinical outcome as measured by hemoglobin A1c (HbA1c). Subjects with type 1 and type 2 diabetes tested with the FreeStyle meter (group 1) or tested with their original meter (group 2). After three months the subjects used the alternate meter. Testing frequency and blood glucose concentrations were recorded for the month before the study began and monthly thereafter. HbA1c was tested initially, at the crossover point, and at study conclusion. Insulin users increased testing frequency from 2.4 to 3.0 tests/day. Testing frequency for non-insulin users remained the same at 1.5 tests/day. Testing frequency was the same with the FreeStyle and the original meters. The average HbA1c was 7.4% (SD 1.5%) initially, 7.3% (SD 1.5%) at the crossover point, and 6.9% (SD 1.1%) at study conclusion. There was no significant difference in HbA1c measurements between meter types. Preference rankings were 76% for FreeStyle, 20% for their original meter, and 4% preferred both meters equally. This population tended to be in good glycemic control with 70% having HbA1c at < or = 8.0 at study initiation. Subjects preferred testing with the FreeStyle meter (76%), but did not increase testing frequency. Study participants tended to be in good testing compliance and glycemic control with little room for improvement. A population in poor glucose control might show differences in outcome with off site monitoring.

Adult↗

PubMed1987

Site-specific recombination directed by single-stranded crossover linkers: specific deletion of the amino-terminal region of the beta-galactosidase gene in pUC plasmids.

The "duplex crossover linker" technique was simplified and used to delete the beta-galactosidase (beta-Gal)-coding sequence upstream from the multiple restriction sites in pUC plasmids. A single-stranded crossover linker, with a homology-searching sequence as short as 5 bases, was initially ligated to a linearized plasmid. Inside Escherichia coli, the plasmid was circularized by intramolecular, homologous recombination between the (5'-or 3'-) protruding homology-searching sequence and a targeted region in the opposite terminus. As a consequence, sequences beyond the point of integration were deleted. Specific deletion of sequences up to 1472 bp was demonstrated. The single-stranded linkers apparently avoided generation of undesirable mutants associated with the usage of duplex linkers. A mechanism has been proposed for the intramolecular recombination directed by the crossover linkers. It principally involves either 3'- or 5'-exonucleolytic breakdown of the homologous terminus of the plasmid, circularization by spontaneous pairing of the exposed complementary strands, and subsequent degradation of any redundant sequence.

Base Sequence↗

PubMed1999

The Saccharomyces cerevisiae MER3 gene, encoding a novel helicase-like protein, is required for crossover control in meiosis.

The MER3 gene is identified as a novel meiosis-specific gene, whose transcript is spliced in an MRE2/MER1-dependent manner. The predicted Mer3 protein contains the seven motifs characteristic of the DExH-box type of helicases as well as a putative zinc finger. Double strand breaks (DSBs), the initial changes of DNA in meiotic recombination, do not disappear completely and are hyperresected late in mer3 meiosis, indicating that MER3 is required for the transition of DSBs to later intermediates. A mer3 mutation reduces crossover frequencies, and the remaining crossovers show random distribution along a chromosome, resulting in a high incidence of non-disjunction of homologous chromosomes at the first meiotic division. MER3 appears to be very important for both the DSB transition and crossover control.

Amino Acid Sequence↗

PubMed1995

Role of reciprocal exchange, one-ended invasion crossover and single-strand annealing on inverted and direct repeat recombination in yeast: different requirements for the RAD1, RAD10, and RAD52 genes.

We have constructed novel DNA substrates (one inverted and three direct repeats) based on the same 0.6-kb repeat sequence to study deletions and inversions in Saccharomyces cerevisiae. Spontaneous deletions occur six to eight times more frequently than inversions, irrespective of the distance between the repeats. This difference can be explained by the observation that deletion events can be mediated by a recombination mechanism that can initiate within the intervening sequence of the repeats. Spontaneous and double-strand break (DSB)-induced deletions occur as RAD52-dependent and RAD52-independent events. Those deletion events initiated through a DSB in the unique intervening sequence require the Rad1/Rad10 endonuclease only if the break is distantly located from the flanking DNA repeats. We propose that deletions can occur as three types of recombination events: the conservative RAD52-dependent reciprocal exchange and the nonconservative events, one-ended invasion crossover, and single-strand annealing (SSA). We suggest that one-ended invasion is RAD52 dependent, whereas SSA is RAD52 independent. Whereas deletions, like inversions, occur through reciprocal exchange, deletions can also occur through SSA or one-ended invasion. We propose that the contribution of reciprocal exchange and one-ended invasion crossover vs. SSA events to overall spontaneous deletions is a feature specific for each repeat system, determined by the initiation event and the availability of the Rad52 protein. We discuss the role of the Rad1/Rad10 endonuclease on the initial steps of one-ended invasion crossover and SSA as a function of the location of the initiation event relative to the repeats. We also show that the frequency of recombination between repeats is the same independent of their location (whether on circular plasmids, linear minichromosomes, or natural chromosomes) and have similar RAD52 dependence.

Chromosome Inversion↗

PubMed1996

Characterization of a meiotic crossover in maize identified by a restriction fragment length polymorphism-based method.

Genetic map lengths do not correlate directly with genome size, suggesting that meiotic recombination is not uniform throughout the genome. Further, the abundance of repeated sequences in plant genomes requires that crossing over is restricted to particular genomic regions. We used a physical mapping approach to identify these regions without the bias introduced by phenotypic selection. This approach is based on the detection of nonparental polymorphisms formed by recombination between polymorphic alleles. In an F2 population of 48 maize plants, we identified a crossover at two of the seven restriction fragment length polymorphism loci tested. Characterization of one recombination event revealed that the crossover mapped within a 534-bp region of perfect homology between the parental alleles embedded in a 2773-bp unique sequence. No transcripts from this region could be detected. Sequences immediately surrounding the crossover site were not detectably methylated, except for an SstI site and at the flanking repetitive sequences were faithfully inherited by the recombinant allele. Our observations suggest that meiotic recombination in maize occurs between perfectly homologous sequences, within unmethylated, nonrepetitive regions of the genome.

Alleles↗

PubMed1999

Chromosome size-dependent control of meiotic reciprocal recombination in Saccharomyces cerevisiae: the role of crossover interference.

In the yeast Saccharomyces cerevisiae, small chromosomes undergo meiotic reciprocal recombination (crossing over) at rates (centimorgans per kilobases) greater than those of large chromosomes, and recombination rates respond directly to changes in the total size of a chromosomal DNA molecule. This phenomenon, termed chromosome size-dependent control of meiotic reciprocal recombination, has been suggested to be important for ensuring that homologous chromosomes cross over during meiosis. The mechanism of this regulation was investigated by analyzing recombination in identical genetic intervals present on different size chromosomes. The results indicate that chromosome size-dependent control is due to different amounts of crossover interference. Large chromosomes have high levels of interference while small chromosomes have much lower levels of interference. A model for how crossover interference directly responds to chromosome size is presented. In addition, chromosome size-dependent control was shown to lower the frequency of homologous chromosomes that failed to undergo crossovers, suggesting that this control is an integral part of the mechanism for ensuring meiotic crossing over between homologous chromosomes.

Chromosomes, Fungal↗

PubMed2002

Crossover interference in the mouse.

We present an analysis of crossover interference in the mouse genome, on the basis of high-density genotype data from two reciprocal interspecific backcrosses, comprising 188 meioses. Overwhelming evidence was found for strong positive crossover interference with average strength greater than that implied by the Carter-Falconer map function. There was some evidence for interchromosomal variation in the level of interference, with smaller chromosomes exhibiting stronger interference. We further compared the observed numbers of crossovers to previous cytological observations on the numbers of chiasmata and evaluated evidence for the obligate chiasma hypothesis.

Animals↗

PubMed2002

Crossover interference in Arabidopsis.

The crossover distribution in meiotic tetrads of Arabidopsis thaliana differs from those previously described for Drosophila and Neurospora. Whereas a chi-square distribution with an even number of degrees of freedom provides a good fit for the latter organisms, the fit for Arabidopsis was substantially improved by assuming an additional set of crossovers sprinkled, at random, among those distributed as per chi square. This result is compatible with the view that Arabidopsis has two pathways for meiotic crossing over, only one of which is subject to interference. The results further suggest that Arabidopsis meiosis has >10 times as many double-strand breaks as crossovers.

Arabidopsis↗

PubMed1974

The distribution of crossovers along unreplicated lambda bacteriophage chromosomes.

The distribution of crossovers along unreplicated chromosomes of bacteriophage lambda has been examined by determining the density distributions and genotypes of particles in the progenies of crosses of density-labeled by ordinary parents in the presence of genetic blocks to replication. The Red and Rec systems combined produce crossovers primarily near the ends (especially the right end) of the chromosome. Removal of the generalized lambda recombination functions by red and gam mutations results in loss of these terminal crossovers; coupled with this loss is a disappearance of the differential dependence of recombination frequencies in terminal and central intervals on DNA synthesis. Removal of the bacterial system by a recA mutation results in severe depression of crossing over among unreplicated phage, with the few recombinants produced by the lambda system occurring near the right end.

Chromosome Mapping↗

PubMed1985

The black/white mortality crossover: investigation in a community-based study.

The black/white mortality crossover at about age 75, a result of lower white mortality rates at younger ages and lower black rates at the oldest ages, has been observed in U.S. vital statistics since 1900. Though a persistant observation in such data, its validity has been challenged by questions about census enumeration and age reporting on death certificates. Analyses of 20 years experience of all-cause mortality in the community-based Evans County Study using a Weibull model of age specific mortality rates showed a statistically significant black/white mortality crossover for both men (at age 73) and women (at age 85). The finding of a crossover in this longitudinally followed population is significant because the age reporting for both survivors and age at death for nonsurvivors were obtained in the study protocol and did not rely on age reporting either in census data or on the death certificate. Differences in the age and sex patterns of mortality between two populations living in the same geographic region are relevant to questions about the etiology of the major age-related chronic diseases as well as to topics of current interest in health care policy.

Adult↗

PubMed1998

High level of unequal meiotic crossovers at the origin of the 22q11. 2 and 7q11.23 deletions.

Interstitial chromosomal deletions at 22q11.2 and 7q11.23 are detected in the vast majority of patients affected by CATCH 22 syndromes and the Williams-Beuren syndrome, respectively. In a group of 15 Williams-Beuren patients, we have shown previously that a large number of 7q11.23 deletions occur in association with an interchromosomal rearrangement, indicative of an unequal crossing-over event between the two homologous chromosomes 7. In this study, we show that a similar mechanism also underlies the formation of the 22q11.2 deletions associated with CATCH 22. In eight out of 10 families with a proband affected by CATCH 22, we were able to show that a meiotic recombination had occurred at the critical deleted region based on segregation analysis of grandparental haplotypes. The incidences of crossovers observed between the closest informative markers, proximal and distal to the deletion, were compared with the expected recombination frequencies between the markers. A significant number of recombination events occur at the breakpoint of deletions in CATCH 22 patients (P = 2.99x10(-7)). The segregation analysis of haplotypes in three-generation families was also performed on an extended number of Williams-Beuren cases (22 cases in all). The statistically significant occurrence of meiotic crossovers (P = 4.45x10(-9)) further supports the previous findings. Thus, unequal meiotic crossover events appear to play a relevant role in the formation of the two interstitial deletions. The recurrence risk for healthy parents in cases where such meiotic recombinations can be demonstrated is probably negligible. Such a finding is in agreement with the predominantly sporadic occurrence of the 22q11.2 and 7q11. 23 deletions. No parent-of-origin bias was observed in the two groups of patients with regard to the origin of the deletion and to the occurrence of inter- versus intrachromosomal rearrangements.

Adolescent↗

PubMed2006

Analysis of non-crossover bivalents in pachytene cells from 10 normal men.

BACKGROUND: Bivalents with no recombination foci (possible achiasmates) are unable to orient properly on the metaphase plate or to segregate chromosomes to daughter cells. Non-crossover bivalents are known to cause meiotic arrest in various organisms. METHODS: Individual non-crossover bivalents were identified in 886 pachytene cells (19 492 bivalents) from testicular biopsies of 10 normal men. Fluorescence staining combined with centromere-specific multicolour fluorescence in situ hybridization (cenM-FISH) was used to identify mismatch repair gene mutation of human mutL homologue 1 (MLH1) recombination foci along each bivalent synaptonemal complex (SC). RESULTS: A total of 60 autosomal non-crossovers (SCs without an MLH1 focus) were found, and of these, chromosomes 21 (2.1%) and 22 (1.7%) had a significantly higher proportion than chromosomes 11, 12, 19 (each 0.1%), 13 (0.2%), 14 (0.6%), 16 (0.5%) and 15, 17, 18, 20 (each 0.3%) (P < 0.05). Sex chromosome univalents had a frequency of 27%, higher than that observed in any autosomal bivalent (P < 0.0001). CONCLUSIONS: These results suggest that G-group chromosomes and sex chromosomes are most susceptible to having no recombination foci and thus would be more susceptible to non-disjunction during spermatogenesis. This is consistent with previous observations from sperm karyotyping and FISH analysis, which demonstrate that chromosomes 21 and 22 and the sex chromosomes have a significantly increased frequency of aneuploidy compared with other autosomes.

Aged↗

PubMed1992

Extensive small-cell lung cancer. A randomized comparison of two chemotherapy programs with early crossover in instances of failure. Association pour le Traitement des Tumeurs Intra-Thoraciques (ATTIT).

Two chemotherapy regimens for patients with extensive small-cell lung cancer were prospectively compared in a randomized multicentric trial with crossover. Every four weeks, 60 consecutive previously untreated patients received either DPE (doxorubicin, cisplatin and etoposide), or CIV (carboplatin, ifosfamide and vincristine) with crossover as soon as progression or end of response were observed. Pretreatment characteristics were similar in the two groups. Fifty-seven patients were evaluated for response. The response rate was higher with the DPE regimen both in first-line (for DPE: response rate 62% (18/29), including 17% (5/29) of complete response (CR), and for CIV: response rate 29% (8/28) with no CR, p < 0.02) and in second-line after crossover (for DPE: response rate 45% (9/20) including 5% (1/20) of CR, and for CIV response rate 0%, p < 0.02). Major toxicities were equally frequent in both groups. No significant difference was found between median survival times (9.7 months for the DPE group and 10.4 months for the CIV group). We conclude that: 1) DPE is a more active regimen than CIV, both in first- and second-line; 2) no alternating scheme may be considered with these two combinations. Of particular note is the similar median survival times in the two groups, contrasting with the different activities of the two regimens.

Adult↗

PubMed2001

Local changes in GC/AT substitution biases and in crossover frequencies on Drosophila chromosomes.

I present here evidence of remarkable local changes in GC/AT substitution biases and in crossover frequencies on Drosophila chromosomes. The substitution pattern at 10 loci in the telomeric region of the X chromosome was studied for four species of the Drosophila melanogaster species subgroup. Drosophila orena and Drosophila erecta are clearly the most closely related species pair (the erecta complex) among the four species studied; however, the overall data at the 10 loci revealed a clear dichotomy in the silent substitution patterns between the AT-biased- substitution melanogaster and erecta lineages and the GC-biased-substitution yakuba and orena lineages, suggesting two or more independent changes in GC/AT substitution biases. More importantly, the results indicated a between- loci heterogeneity in GC/AT substitution bias in this small region independently in the yakuba and orena lineages. Indeed, silent substitutions in the orena lineage were significantly biased toward G and C at the consecutive yellow, lethal of scute, and asense loci, but they were significantly biased toward A and T at sta. The substitution bias toward G and C was centered in different areas in yakuba (significantly biased at EG:165H7.3, EG:171D11.2, and suppressor of sable). The similar silent substitution patterns in coding and noncoding regions, furthermore, suggested mutational biases as a cause of the substitution biases. On the other hand, previous study reveals that Drosophila yakuba has about 20-fold higher crossover frequencies in the telomeric region of the X chromosome than does D. melanogaster; this study revealed that the total genetic map length of the yakuba X chromosome was only about 1.5 times as large as that of melanogaster and that the map length of the X-telomeric y-sta region did not differ between Drosophila yakuba and D. erecta. Taken together, the data strongly suggested that an approximately 20- fold reduction in the X-telomeric crossover frequencies occurred in the ancestral population of D. melanogaster after the melanogaster-yakuba divergence but before the melanogaster-simulans divergence.

Animals↗

PubMedDate not supplied

Topiramate in trigeminal neuralgia: a randomized, placebo-controlled multiple crossover pilot study.

We conducted a pilot study to evaluate the efficacy of topiramate in trigeminal neuralgia using a randomized, double-blind, placebo-controlled, two-period crossover design. Three patients were enrolled in and completed the study. All three patients responded to topiramate in this main study and entered a subsequent confirmatory study consisting of three topiramate-placebo crossovers. In the main study, topiramate reduced pain by 31%, 42%, and 64% in the three patients (p = 0.04). However, topiramate showed no effect in the confirmatory study. Given that trials of less common pain conditions are fraught with low patient recruitment rates, a multiple crossover design provides more information, which is important in conditions associated with considerable pain fluctuation. Larger trials are needed to more precisely estimate the effect of topiramate in trigeminal neuralgia.

Adult↗

PubMed1995

Facilitation of internal jugular venous cannulation using an audio-guided Doppler ultrasound vascular access device: results from a prospective, dual-center, randomized, crossover clinical study.

OBJECTIVE: To determine the utility of an audio-guided Doppler ultrasound device in improving success and decreasing complications in cannulation of the internal jugular vein in high-risk patients. DESIGN: Prospective, randomized, crossover clinical study. SETTING: Two major university medical centers in critical care environments. PATIENTS: Seventy-six consecutive, consenting adult patients with preexisting obesity or coagulopathy requiring central venous access. INTERVENTIONS: Subjects enrolled in the study were randomized to receive either the traditional "blind" (control) technique or the ultrasonic technique. A maximum of three cannulation attempts were allowed before crossover to three attempts with the alternative technique. All cannulations were attempted via the internal jugular vein through a high/central approach. RESULTS: Patient and operator characteristics were similar between groups. The initial use of an audio-guided ultrasound device was associated with increased success of cannulation (84.4% vs. 61.4%; p < .05) and decreased need to crossover to the alternative technique. Success on the first needle pass was more likely with the ultrasound technique (56.3% vs. 29.5%; p < .05). Significant complications were greater with the control technique (carotid artery puncture 16.3% vs. 2.0% [p < .02]; any significant complication 26.5% vs. 6.1% [p < .01]). CONCLUSIONS: The use of an audio-guided Doppler ultrasound vascular access device was associated with increased success of cannulation and a decreased frequency of significant complications in a population of high-risk patients with obesity or coagulopathy.

Catheterization, Central Venous↗

PubMed2001

Pindolol augmentation in aggressive schizophrenic patients: a double-blind crossover randomized study.

Treatment of aggression in schizophrenic patients is a major challenge. We sought to examine the efficacy of augmentation of antipsychotic treatment with pindolol in the amelioration of aggression. Thirty male inpatients meeting DSM-IV criteria for schizophrenia, aged 20-65 years involved in four or more aggressive incidents in the two previous months, were enrolled in a double-blind crossover study. Aggression was evaluated per incident, with the Overt Aggression Scale (OAS). Positive and Negative Syndrome Scale (PANSS) was administered at baseline, crossover and at endpoint. Patients received either pindolol or placebo augmentation 5 mg x three times a day until crossover, then switched. No significant differences were found in the PANSS scores between the placebo and pindolol treatments. OAS scores were significantly reduced for number of aggressive incidents towards objects and other persons during pindolol treatment (0.59 versus 1.46, F = 6.09, P < 0.02; 1.96 versus 3.23, F = 4.17, P < 0.05, respectively). Similar results were obtained for severity of incidents (0.89 versus 3.58, F = 19.42, P < 0.0001; 2.89 versus 6.85, F = 10.11, P < 0.004, respectively). Pindolol, with its dual beta and 5-HT1A blocking effect ameliorated both number and severity of aggressive acts. Influence on severity may be associated with a 5-HT1A antagonistic effect.

Administration, Oral↗

PubMedDate not supplied

Nutrient balance studies in the preterm infant: crossover and parallel studies as methods of experimental design.

Crossover and parallel studies were compared as methods of experimental design during nutritional balance studies in the preterm infant. Twelve formula-fed infants (birth weight, 1,362 +/- 125 g, mean SD; gestational age, 32.3 +/- 1.7 weeks) were studied over 2 continuous weeks, "period" being the only obvious difference between the weeks. During each week, growth was determined, and 84-h nutrient balance was performed. Growth was adequate during both weeks. Increased absorption and retention (mg/kg/day and percent) of calcium and copper were noted during the 2nd week. Increased retention (mg/kg/day and percent) of phosphorus and magnesium was noted also, indicating increased nutrient assimilation due to a period effect. However, the variance due to the period effect (crossover) was less than that associated with "patient characteristics" (parallel study). In addition, sample size requirements were less, indicating that crossover studies are more efficient than parallel studies as a method of experimental design.

Analysis of Variance↗