Biomedical subjects

A Nicolas

Publications and source records attributed to A Nicolas.

At least 37 records · Page 2Linked to original sources

PubMed2001

[Sleep and aging].

A COMMON DISORDER: Sleep is one of the most often altered functions in elderly people. Obviously, insomnia is one of the main complain, inducing benzodiazepine (BSD) abuse, but we must keep in mind that sleep apnoea syndrome (SAS) and restless legs syndrome (RLS) are also frequent in this group of age. After exclusion of the various age-related conditions that could induce sleep disorders, we must focalise on primary and secondary sleep disorders. As an introduction, methods of sleep analysis are described and qualitative and quantitative sleep variables are given. PHYSIOLOGICAL SLEEP: Comparing the sleep of elderly people to the one of young adult give us the opportunity to define the limits of the physiological sleep aging. It seems that the main age-induced sleep disturbances are problems to maintain sleep and chronobiological disorganisation of the sleep-wake rhythm, both responsible for insomnia complains. It is important to note that SAS and RLS prevalence are correlated with age. Also crucial is the complex association between sleep, depression and dementia. These interactions are addressed from a diagnostic and a therapeutic point of view. THERAPEUTIC APPROACH: Lastly, concerning insomnia we emphasise the importance of therapeutic alternative to BZD, responsible for addictions and cognitive impairment, mainly behavioural and chronotherapeutic methods (phototherapy, melatonin). For clinicians, it is recommended to respect the individual rhythms of each elderly patient and to prefer nonpharmacological methods.

Age Factors↗

PubMed2001

B-type cyclins CLB5 and CLB6 control the initiation of recombination and synaptonemal complex formation in yeast meiosis.

BACKGROUND: The life cycle of most eukaryotic organisms includes a meiotic phase, in which diploid parental cells produce haploid gametes. During meiosis a single round of DNA replication is followed by two rounds of chromosome segregation. In the first, or reductional, division (meiosis I), which is unique to meiotic cells, homologous chromosomes segregate from one another, whereas in the second, or equational, division (Meiosis II) sister centromeres disjoin. Meiotic DNA replication precedes the initiation of recombination by programmed Spo11-dependent DNA double-strand breaks. Recent reports that meiosis-specific cohesion is established during meiotic S phase and that the length of S phase is modified by recombination factors (Spo11 and Rec8) raise the possibility that replication plays a fundamental role in the recombination process. RESULTS: To address how replication influences the initiation of recombination, we have used mutations in the B-type cyclin genes CLB5 and CLB6, which specifically prevent premeiotic replication in the yeast Saccharomyces cerevisiae. We find that clb5 and clb5 clb6 but not clb6 mutants are defective in DSB induction and prior associated changes in chromatin accessibility, heteroallelic recombination, and SC formation. The severity of these phenotypes in each mutant reflects the extent of replication impairment. CONCLUSIONS: This assemblage of phenotypes reveals roles for CLB5 and CLB6 not only in DNA replication but also in other key events of meiotic prophase. Links between the function of CLB5 and CLB6 in activating meiotic DNA replication and their effects on subsequent events are discussed.

Cyclin B↗

PubMed2001

Sleep spindle characteristics in healthy subjects of different age groups.

OBJECTIVES: Few studies have quantified the various characteristics of sleep spindles (SS) in groups of normal human subjects. The aim of the present study was to look at the effects of age on the number, density, duration, intra-spindle frequency, and periodicity of SS during stage 2 sleep in normal subjects of different age groups. METHODS: Thirty-six healthy subjects participated in the study. They were divided into 6 age groups: 10-19, 20-29, 30-39, 40-49, 50-59 and 60-69 years. RESULTS: The results show that there is a progressive decrease in SS number, density, duration and a progressive increase in intra-spindle frequency with age. These changes occur mainly in the first 4 decades, except for SS number and density, for which the changes seem to continue until the sixth decade. The present study also reveals a clear periodicity of SS in human sleep. SS occur every 3-6 s, and the modal value of inter-spindle intervals increases with aging. CONCLUSIONS: The progressive decrease in the number of SS and slow-wave sleep time with age suggests that SS are part of sleep promoting mechanisms. The negative correlation found between SS density and sleep efficiency in the present study is congruent with the sleep maintenance role of SS.

Adult↗

PubMed2001

Enantioseparation of flobufen with cyclodextrins studied by capillary electrophoresis and NMR.

PURPOSE: The aim of this study was to obtain the resolution of flobufen enantiomers, an antiinflammatory active substance, by capillary electrophoresis with cyclodextrins. The mechanism of complexation and determination of the stoichiometry of the complexes were studied by NMR and the analytical method was developed and validated. METHODS: Zone capillary electrophoresis coupled to direct ultraviolet detection was selected. The interaction between flobufen and the chiral selector was studied by NMR. Optimization of the separation was performed using a Box-Wilson Central Composite Design for three factors related to the composition of the electrolyte. RESULTS: Heptakis (2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD) was found to be the most efficient selector via the formation of a 1:1 complex proved by NMR. Constants of complexation of flobufen enantiomers were determined by NMR and capillary electrophoresis. Optimal values for the critical factors of the analytical system were: pH (5.50), content in methanol (10% v/v), and TM-beta-CD (30 mM). The ability of capillary electrophoresis to quantify as low as 0.1% (w/w) of R in S-flobufen or vice-versa was established. CONCLUSIONS: Capillary electrophoresis was shown to be a valuable method to control the enantiocomposition of flobufen by use of a chiral selector whose interactions with the analytes could be explored by NMR.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2001

Leiomyosarcomas and most malignant fibrous histiocytomas share very similar comparative genomic hybridization imbalances: an analysis of a series of 27 leiomyosarcomas.

Twenty-seven tumor samples with a diagnosis of leiomyosarcomas (LMS) were characterized by comparative genomic hybridization. The results were compared with immunohistochemical analysis of the smooth muscle profile of the tumors and expression of the RB1 gene protein. The comparative genomic hybridization profiles suggested that 7 of the 27 tumors might have been misclassified. High levels of DNA amplification were detected in 20 different small regions and recurrently involved bands 1p34, q21, 12q13-15, 17p, and 22q. Most recurrent simple gains were noted at sites such as 1p3, 1q21, 15q12-15, 16p, 17p and 17q, 19, 20q, 22q, and Xp. Significant losses of chromosome 13 were detected in 19 of the 27 tumors with a putative common region of loss in bands 13q14-21. Losses of chromosomes 1q, 2p and 2q, 4q, 9p, 10p and 10q, 11p and 11q23, and 16q were also highly recurrent. A comparative analysis between the most frequent genomic imbalances observed in this study of LMS and the genomic imbalances observed in a large proportion of malignant fibrous histiocytomas (MFH) from a previous study demonstrated that both types of tumors had similar recurrent imbalances. Although MFH were once thought to be a separate member of the soft tissue sarcoma family, our observations support the hypothesis that MFH are a morphologic modulation in the tumoral progression of other sarcomas, particularly LMS.

Adult↗

PubMed2000

POL32, a subunit of the Saccharomyces cerevisiae DNA polymerase delta, defines a link between DNA replication and the mutagenic bypass repair pathway.

Pol32 is a subunit of Saccharomyces cerevisiae DNA polymerase delta required in DNA replication and repair. To gain insight into the function of Pol32 and to determine in which repair pathway POL32 may be involved, we extended the analysis of the pol32delta mutant with respect to UV and methylation sensitivity, UV-induced mutagenesis; and we performed an epistasis analysis of UV sensitivity by combining the pol32delta with mutations in several genes for postreplication repair (RA D6 group), nucleotide excision repair (RAD3 group) and recombinational repair (RAD52 group). These studies showed that pol32delta is deficient in UV-induced mutagenesis and place POL32 in the error-prone RAD6/ REV3 pathway. We also found that the increase in the CAN1 spontaneous forward mutation of different rad mutators relies entirely or partially on a functional POL32 gene. Moreover, in a two-hybrid screen, we observed that Pol32 interacts with Srs2, a DNA helicase required for DNA replication and mutagenesis. Simultaneous deletion of POL32 and SRS2 dramatically decreases cellular viability at 15 degrees C and greatly increases cellular sensitivity to hydroxyurea at the permissive temperature. Based on these findings, we propose that POL32 defines a link between the DNA polymerase and helicase activities, and plays a role in the mutagenic bypass repair pathway.

DNA Polymerase III↗

PubMed2000

ERBB2 overexpression in breast carcinomas: no positive correlation with complete pathological response to preoperative high-dose anthracycline-based chemotherapy.

The predictive value of ERBB2 amplification/expression to doxorubicin use is controversial. Preoperative chemotherapy, followed by the pathological assessment of tumour response to treatment provide optimal conditions for the evaluation of the predictive value of biological parameters. We report here data on the predictive value of ERBB2 in a series of 54 cases of breast cancer treated by preoperative high-dose anthracycline-based chemotherapy. Our series consisted of 26 women presenting an inflammatory breast cancer (IBC) and of 28 women with poor prognosis primary cancer (PPPC). Patients received a total of four cycles with doxorubicin (75 mg/m(2) for IBC or 70 mg/m(2) for PPPC) and cyclophosphamide (6 g/m(2) for IBC or 1400 mg/m(2) for PPPC), every 21 days. ERBB2 expression was determined by immunohistochemistry (clone CB11) performed on a tumour biopsy taken before chemotherapy. All patients underwent surgery as a second step of treatment, and the tumour response was assessed on pathological specimens. A complete pathological response was observed in 24 of the 54 cases (44%) (95% confidence interval (CI), 31-57). Pathological complete response was positively correlated with high histological grade (P=0. 02) and with the absence of oestrogen (P=0.003) or progesterone (P=0. 02) receptor expression. ERBB2 overexpression was found in 18 of the 54 cases (33%). A complete pathological response was observed in 33% of these cases (6/18). This figure was not significantly different from the 50% rate of complete response observed for tumours with no detectable ERBB2 expression (18/36). In this small series, ERBB2 overexpression was not a significant predictive marker of the pathological response to high-dose doxorubicin-based chemotherapy.

Adult↗

PubMed2000

Strong correlation between results of fluorescent in situ hybridization and immunohistochemistry for the assessment of the ERBB2 (HER-2/neu) gene status in breast carcinoma.

ERBB2 (HER-2/neu) amplification and/or overexpression are associated with poor prognosis in node-positive breast carcinoma. Its prognostic value in node-negative cases and its predictive value for response to chemotherapy remain controversial. This may be related to the use of molecular methods, which are sensitive to dilution of tumor material by normal cells, or the use of nonstandardized immunohistochemistry (IHC) procedures, for the determination of the ERBB2 gene status. In addition, new therapeutic approaches that target the cells overexpressing ERBB2 are under development. These perspectives necessitate a reliable evaluation of the status of ERBB2 in individual tumors before the application of specific therapeutic strategies. Fluorescent in situ hybridization (FISH) and IHC allow the evaluation of the ERBB2 status specifically in tumor cells on archival material. We have analyzed a series of 100 invasive ductal breast carcinomas without lymph node invasion both by IHC, using the CB11 monoclonal antibody and a sensitive Auidin Biotin Complex (ABC) immunodetection system, and by FISH, using the Oncor Inform HER-21neu (ERBB2) gene amplification detection system as reference technique. Complete concordance between the results of FISH and IHC was seen in 98% of the cases. ERBB2 amplification (more than four signals per nucleus) was observed in 12 of the 100 cases, and all but one showed an overexpression of the protein (membrane staining) by IHC. Conversely, ERBB2 expression was present in one case without gene amplification. In conclusion, ERBB2 overexpression detected by IHC is highly correlated to gene amplification detected by FISH. Thus, under standardized conditions, IHC is a reliable and economical test to assess the ERBB2 status in tumors. The use of FISH could be limited to the verification of the status of tumors displaying a weak membrane immunostaining.

Breast Neoplasms↗

PubMed2000

High sensitivity and specificity of immunohistochemistry for the detection of hormone receptors in breast carcinoma: comparison with biochemical determination in a prospective study of 793 cases.

AIMS: The hormone receptor (HR) status of breast cancer is an important prognostic factor and predictive parameter of the response to hormone therapy. Enzyme immunoassay (EIA) is currently the standard for determination of HR, but immunohistochemistry (IHC) represents a potentially useful alternative. We used IHC to determine HR status in a large prospective study and compared the results to those obtained by EIA. This study was designed to determine which technique should be used in daily practice in our institution which manages a large number of patients. METHODS AND RESULTS: Oestrogen (ER) and progesterone (PgR) receptor status was evaluated in a prospective series of 793 infiltrating breast cancers by IHC in paraffin-embedded tissue sections, using antibodies 6F11 and 1A6, with a rigorous quality control of the methodology. ER were found to be significantly expressed in 81% of cases after IHC analysis and in 78% of cases by EIA. For PgR, the respective rates of positivity were 65% and 69%. The tumour HR level detected by either technique was significantly correlated with the value of tumour size, histological grade and S-phase fraction. A significant link was observed between the percentage of labelled cells after IHC analysis and the amount of protein detected by EIA. Critical analysis of discordance found that, in the group of invasive lobular carcinomas, the rate of HR positivity was higher with IHC (84%) than with EIA (45%) and that, in the overall population, IHC was more specific than EIA, since cases with nonrelevant positivity related to intraductal normal or neoplastic cells expressing HR could be discarded. The cost of IHC analysis was found to be about one-third of that of EIA. CONCLUSIONS: IHC is more sensitive, specific and economical than EIA. It should constitute the new standard technique provided that good quality assurance procedures are respected.

Antibodies, Monoclonal↗

PubMed2000

Low expression of bcl-2 in Brca1-associated breast cancers.

Little data are available concerning the molecular mechanisms of action of Brca1 and Brca2 in breast oncogenesis. Recent experimental results suggest that Brca1 plays a role in the regulation of apoptosis. In order to determine whether the analysis of human tumours would provide data supporting this hypothesis, we have assessed the expression of the antiapoptotic bcl-2 and of the proapoptotic p53 genes in Brca1 - and Brca2 -associated breast carcinomas. The levels of expression of these genes were compared to those observed in controls and to the mitotic and the apoptotic indexes. Our series were composed of 16 cases of breast carcinoma in women with a germline Brca1 gene mutation, and of four cases with Brca2 mutation. A group of 39 patients aged under 36 years and for whom the search for Brca1 gene mutations was negative, and a group of 36 cases of sporadic cancers without data on their Brca status were used as controls. Immunohistochemistry was used to detect p53 and bcl-2 gene products. Mitotic and apoptotic indexes were higher in Brca1 -associated tumours than in controls. No significant difference in p53 immunostaining was observed between the four groups of patients. In contrast, the rate of bcl-2 -positive tumours was lower (31%) in Brca1 -carcinomas than in carcinomas without Brca1 mutation (90%) (P< 10(-3)). A strong Bcl-2 expression was found in the four cases of Brca2 -associated carcinomas. No significant correlation was observed between p53 and Bcl-2 immunostainings, either in cases or in controls. The association between Brca1 status and Bcl-2 expression remained significant after adjustment for the oestrogen receptor status. Our study shows that a low expression of bcl-2 characterises most Brca1 -associated breast carcinomas, a biological trait which seems not to be shared by Brca2 -associated tumours nor to be related to oestrogen receptor and/or p53 status. bcl-2 might thus be one of the target genes involved in the oncogenesis related to Brca1 and its down-regulation may account for the increased apoptosis and the high proliferative rate observed in Brca1 -associated carcinomas.

Adult↗

PubMed1999

Disruption and functional analysis of seven ORFs on chromosome IV: YDL057w, YDL012c, YDL010w, YDL009c, YDL008w (APC11), YDL005c (MED2) and YDL003w (MCD1).

In the context of the EUROFAN project, we have carried out the systematic disruption of seven ORFs on chromosome IV of Saccharomyces cerevisiae using the long flanking homology technique to replace each ORF with the KanMX cassette. Targeted disruption of YDL057w, YDL012c, or YDL010w with YDL009c (the two ORFs overlap) confers no overt defects in haploid growth on a variety of media at different temperatures, in mating, or in the sporulation of diploids homozygous for the disruption. By contrast, YDL008w and YDL003w disruptants are non-viable. The product of YDL008w (elsewhere identified as APC11) is a component of the anaphase promoting complex. YDL003w (also termed MCD1) is a homologue of Schizosaccharomyces pombe rad21, an essential gene implicated in DNA double-strand break repair and nuclear organization in fission yeast. In budding yeast, this ORF has been shown by several laboratories to encode a protein involved in sister chromatid cohesion and chromosome condensation. The remaining ORF, YDL005c (also termed MED2), encodes a component of the transcriptional activator complex known as Mediator. Disruption of YDL005c confers a modest slow growth phenotype on rich medium and a more severe phenotype on minimal medium, aberrant cellular morphology, and mating defects; diploids homozygous for the disruption cannot sporulate.

Cell Division↗

PubMed1999

Restless legs syndrome improved by pramipexole: a double-blind randomized trial.

BACKGROUND: Restless legs syndrome (RLS) is characterized by leg paresthesia associated with an irresistible urge to move. Currently used dopaminergic agents, such as levodopa, pergolide, and bromocriptine, offer incomplete control of sensory and motor symptoms and induce severe side effects. OBJECTIVE: To assess the safety and efficacy of pramipexole, a full D3-receptor agonist, in the treatment of RLS. METHODS: Ten RLS patients were studied before and after two 1-month treatments (placebo and pramipexole) administered in a double-blind crossover fashion. The severity of sensory and motor manifestations was assessed by 1 week of home questionnaires and 2 consecutive nights of sleep laboratory recordings. The indexes of periodic leg movement during sleep (PLMS) and during wakefulness (PLMW) were used as primary outcome variables. RESULTS: Pramipexole dramatically reduced the PLMS index to normal values (Wilcoxon, p = 0.005). The PLMW index was also significantly reduced (Wilcoxon, p = 0.007). Pramipexole also alleviated leg discomfort at bedtime and during the night as measured by the home questionnaires. CONCLUSIONS: Pramipexole is the most potent therapeutic agent ever tested for RLS. Measures of both sensory and motor functions returned to normal values after treatment. Moreover, these results further support the hypothesis that D3 receptors play a major role in the physiopathology of this condition.

Adult↗

PubMed1999

EEG and cardiac activation during periodic leg movements in sleep: support for a hierarchy of arousal responses.

OBJECTIVE: To investigate other physiologic changes that occur with periodic leg movements during sleep (PLMS) that might be considered to be more sensitive indices of sleep fragmentation. BACKGROUND: Although PLMS are associated with recurrent microarousals (MA), the frequency of PLMS with MA does not correlate with objective daytime sleepiness. It is postulated that the lack of correlation results from the low sensitivity of the standard criteria used to score MA. METHODS: Ten drug-free patients with a polygraphic and clinical diagnosis of restless legs syndrome (RLS) and PLMS were examined. The EEG correlates of PLMS were analyzed by visual scoring and spectral analysis during PLMS that ended in a visible microarousal (PLMS with MA) or not (PLMS without MA). The R-R interval in the EKG signal was also examined. RESULTS: A total of 34% of PLMS were associated with MA lasting >3 seconds, and 3% of PLMS were associated with MA lasting <3 seconds. Although PLMS with MA were associated with an increase in alpha activity, for PLMS without MA a significant increase in delta and theta activity was present. Both types of PLMS induced a shortening of the R-R interval; this was particularly more marked for PLMS with MA. CONCLUSIONS: First, visual scoring of MA that include a duration of less than 3 seconds has little effect on the detection of PLMS with MA. Second, EEG activation and tachycardia are present during both types of PLMS. Third, a hierarchy in the arousal response is present-going from autonomic activation to bursts of delta activity to alpha activity to a full awakening.

Analysis of Variance↗

PubMed1999

Disruption and functional analysis of six ORFs on chromosome XV: YOL117w, YOL115w ( TRF4), YOL114c, YOL112w ( MSB4), YOL111c and YOL072w.

We have carried out the systematic disruption of six ORFs on chromosome XV, of Saccharomyces cerevisiae using the long flanking homology technique to replace each with the KanMX cassette; we have also constructed plasmids containing replacement cassettes and cognate clones for each ORF. Disruption of three of the ORFs-YOL117w, YOL114c, and YOL112w (also known as MSB4)-does not result in any noteworthy phenotype with respect to temperature or nutritional requirements, but yol112w mutants with an additional disruption of YNL293w, which encodes a protein similar to Yol112w, exhibit a slow growth phenotype. The protein specified by YOL114c shares similarity with the human DS-1 protein. Disruption of YOL115w confers slow growth, cold sensitivity and poor sporulation; this ORF has been described elsewhere as TRF4, which encodes a topoisomerase I-related protein. Cells with disruptions of YOL111c, whose product is weakly similar to the human ubiquitin-like protein GdX, are slightly impaired in mating. Mutants disrupted for YOL072w, the predicted product of which is unrelated to any protein of known function, grow slowly, are cold-sensitive and sporulate with reduced efficiency.

Chromosomal Proteins, Non-Histone↗

PubMed1999

Simultaneous measurement of reactive oxygen species and reduced glutathione using capillary electrophoresis and laser-induced fluorescence detection in cultured cell lines.

A capillary zone electrophoretic (CZE) method coupled with laser-induced fluorescence (LIF) was developed for the simultaneous determination of two important intracellular parameters related to oxidative stress (i.e. reactive oxygen species, ROS, and reduced glutathione, GSH). This rapid and sensitive method was applied to the study of oxidative stress in cultured V79 fibroblast cells. The fluorogenic reagents selected were: (i) dihydrorhodamine-123 (DHR-123) which is converted intracellularly by ROS to the fluorescent rhodamine-123 dye (Rh-123), and (ii) naphthalene-2,3-dicarboxaldehyde (NDA), which reacts quickly with GSH in cell extracts to produce a fluorescent adduct. Separation of Rh-123, GSH-NDA and gamma-glutamylcysteine-NDA adducts was performed using an uncoated fused-silica capillary and a 100 mM borate buffer, pH 9.2, at 20 degrees C and at an applied voltage of 25 kV; LIF detection was operated using an argon laser. The cell line was also tested for its ability to alleviate oxidative stress induced by tert-butylhydroperoxide (t-BuOOH). Exposure to t-BuOOH (up to 3 mm for 2 h) did not affect the intracellular ROS and GSH concentrations. At higher (4-10 mM) t-BuOOH concentrations, an inverse relationship between the concentrations of ROS and GSH was obtained, showing that the present method can readily evaluate the gradual consumption of the primary cellular scavenger of ROS which occurs simultaneously with the increase of oxidative insult.

Animals↗

PubMed1999

The influence of sex, age and sleep/wake state on characteristics of periodic leg movements in restless legs syndrome patients.

Restless legs syndrome (RLS) patients experience periodic stereotyped leg movements while awake and during sleep. The aim of the present study was to measure the effects of sex, age and the sleep/wake state on several characteristics (frequency, duration and periodicity) of these periodic leg movements (PLM). One hundred unrelated patients diagnosed with primary RLS were studied. During wakefulness, frequency of PLM increased and the mean inter-movement interval decreased with advancing age. The modal value of inter-movement interval distribution was also altered suggesting that aging influences rhythm-generation mechanisms. Sleep/wake states had a profound effect on leg movement characteristics. Movements of longer duration were seen during wakefulness, while REM sleep was characterized by the shorter duration and the lowest frequency of PLM, due most likely to the inhibition of spinal motoneurons that prevails in REM sleep. States of vigilance also modulated the periodicity of PLM. Intervals were shorter during wakefulness and increased progressively from stage 1 to stage 2 sleep, and to slow wave sleep (SWS). During REM, the duration of sleep intervals returned to values obtained in stage 1 sleep; these two stages sharing similar patterns of EEG activity. These results indicate that a single state dependent mechanism may be responsible for the periodicity of PLM noted both during sleep and wakefulness.

Adult↗

PubMed1999

Meiotic instability of human minisatellite CEB1 in yeast requires DNA double-strand breaks.

Minisatellites are tandemly repeated DNA sequences of 10-100-bp units. Some minisatellite loci are highly unstable in the human germ line, and structural analysis of mutant alleles has suggested that repeat instability results from a recombination-based process. To provide insights into the molecular mechanism of human minisatellite instability, we developed Saccharomyces cerevisiae strains carrying alleles of the most unstable human minisatellite locus, CEB1 (ref. 2). We observed that CEB1 is destabilized in meiosis, resulting in a variety of intra- and inter-allelic gains or losses of repeat units, similar to rearrangements described in humans. Using mutations affecting the initiation of recombination (spo11) or mismatch repair (msh2 pms1 ), we demonstrate that meiotic destabilization depends on the initiation of homologous recombination at nearby DNA double-strand break (DSBs) sites and involves a 'rearranged heteroduplex' intermediate. Most of the human and yeast data can be explained and unified in the context of DSB repair models.

Alleles↗

PubMed1999

CYS3, a hotspot of meiotic recombination in Saccharomyces cerevisiae. Effects of heterozygosity and mismatch repair functions on gene conversion and recombination intermediates.

We have examined meiotic recombination at the CYS3 locus. Genetic analysis indicates that CYS3 is a hotspot of meiotic gene conversion, with a putative 5'-3' polarity gradient of conversion frequencies. This gradient is relieved in the presence of msh2 and pms1 mutations, indicating an involvement of mismatch repair functions in meiotic recombination. To investigate the role of mismatch repair proteins in meiotic recombination, we performed a physical analysis of meiotic DNA in wild-type and msh2 pms1 strains in the presence or absence of allelic differences at CYS3. Neither the mutations in CYS3 nor the absence of mismatch repair functions affects the frequency and distribution of nearby recombination-initiating DNA double-strand breaks (DSBs). Processing of DSBs is also similar in msh2 pms1 and wild-type strains. We conclude that mismatch repair functions do not control the distribution of meiotic gene conversion events at the initiating steps. In the MSH2 PMS1 background, strains heteroallelic for frameshift mutations in CYS3 exhibit a frequency of gene conversion greater than that observed for either marker alone. Physical analysis revealed no modification in the formation of DSBs, suggesting that this marker effect results from subsequent processing events that are not yet understood.

Alleles↗