Dataset Information

Transcription-associated R-loop formation across the human FMR1 CGG-repeat region.

ABSTRACT: Expansion of a trinucleotide (CGG) repeat element within the 5' untranslated region (5'UTR) of the human FMR1 gene is responsible for a number of heritable disorders operating through distinct pathogenic mechanisms: gene silencing for fragile X syndrome (>200 CGG) and RNA toxic gain-of-function for FXTAS (? 55-200 CGG). Existing models have focused almost exclusively on post-transcriptional mechanisms, but co-transcriptional processes could also contribute to the molecular dysfunction of FMR1. We have observed that transcription through the GC-rich FMR1 5'UTR region favors R-loop formation, with the nascent (G-rich) RNA forming a stable RNA:DNA hybrid with the template DNA strand, thereby displacing the non-template DNA strand. Using DNA:RNA (hybrid) immunoprecipitation (DRIP) of genomic DNA from cultured human dermal fibroblasts with both normal (? 30 CGG repeats) and premutation (55

SUBMITTER: Loomis EW

PROVIDER: S-EPMC3990486 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Transcription-associated R-loop formation across the human FMR1 CGG-repeat region.

Loomis Erick W EW Sanz Lionel A LA Chédin Frédéric F Hagerman Paul J PJ

PLoS genetics 20140417 4

Expansion of a trinucleotide (CGG) repeat element within the 5' untranslated region (5'UTR) of the human FMR1 gene is responsible for a number of heritable disorders operating through distinct pathogenic mechanisms: gene silencing for fragile X syndrome (>200 CGG) and RNA toxic gain-of-function for FXTAS (∼ 55-200 CGG). Existing models have focused almost exclusively on post-transcriptional mechanisms, but co-transcriptional processes could also contribute to the molecular dysfunction of FMR1. W ...[more]

PMID: 24743386

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Project description:BACKGROUND:Fragile-X-Mental-Retardation-1- (FMR1)-gene is supposed to be a key gene for ovarian reserve and folliculogenesis. It contains in its 5'-UTR a triplet-base-repeat (CGG), that varies between 26 and 34 in general population. CGG-repeat-lengths with 55-200 repeats (pre-mutation?=?PM) show instable heredity with a tendency to increase and are associated with premature-ovarian-insufficiency or failure (POI/POF) in about 20%. FMR1-mRNA-expression in leucocytes and granulosa cells (GCs) increases with CGG-repeat-length in PM-carriers, but variable FMR1-expression profiles were also described in women with POI without PM-FMR1 repeat-length. Additionally, associations between low numbers of retrieved oocytes and elevated FMR1-expression levels have been shown in GCs of females with mid-range PM-CGG-repeats without POI. Effects of FMR1-repeat-lengths-deviations (n?<?26 or n?>?34) below the PM range (n?<?55) on ovarian reserve and response to ovarian stimulation remain controversial. METHODS:We enrolled 229 women undergoing controlled ovarian hyperstimulation for IVF/ICSI-treatment and devided them in three ovarian-response-subgroups: Poor responder (POR) after Bologna Criteria, polycystic ovary syndrome (PCO) after Rotterdam Criteria, or normal responder (NOR, control group). Subjects were subdivided into six genotypes according to their be-allelic CGG-repeat length. FMR1-CGG-repeat-length was determined using ALF-express-DNA-sequencer or ABI 3100/3130?×?1-sequencer. mRNA was extracted from GCs after follicular aspiration and quantitative FMR1-expression was determined using specific TaqMan-Assay and applying the ??CT method. Kruskall-Wallis-Test or ANOVA were used for simple comparison between ovarian reserve (NOR, POR or PCO) and CGG-subgroups or cohort demographic data. All statistical analysis were performed with SPSS and statistical significance was set at p???0.05. RESULTS:A statistically significant increase in FMR1-mRNA-expression-levels was detected in GCs of PORs with heterozygous normal/low-CGG-repeat-length compared with other genotypes (p?=?0.044). CONCLUSION:Female ovarian response may be negatively affected by low CGG-alleles during stimulation. In addition, due to a low-allele-effect, folliculogenesis may be impaired already prior to stimulation leading to diminished ovarian reserve and poor ovarian response. A better understanding of FMR1 expression-regulation in GCs may help to elucidate pathomechanisms of folliculogenesis disorders and to develop risk-adjusted treatments for IVF/ICSI-therapy. Herewith FMR1-genotyping potentially provides a better estimatation of treatment outcome and allows the optimal adaptation of stimulation protocols in future.

Project description:The presence of AGG interruptions in the CGG repeat locus of the fragile X mental retardation 1 (FMR1) gene decreases the instability of the allele during transmission from parent to child, and decreases the risk of expansion of a premutation allele to a full mutation allele (the predominant cause of fragile X syndrome) during maternal transmission.To strengthen recent findings on the utility of AGG interruptions in predicting instability or expansion to a full mutation of FMR1 CGG repeat alleles, we assessed the outcomes of 108 intermediate (also named gray zone) and 710 premutation alleles that were transmitted from parent to child, and collected from four international clinical sites. We have used the results to revise our initial model that predicted the risk of a maternal premutation allele expanding to a full mutation during transmission and to test the effect of AGG interruptions on the magnitude of expanded allele instability of intermediate or premutation alleles that did not expand to a full mutation.Consistent with previous studies, the number of AGG triplets that interrupts the CGG repeat locus was found to influence the risk of allele instability, including expansion to a full mutation. The total length of the CGG repeat allele remains the best predictor of instability or expansion to a full mutation, but the number of AGG interruptions and, to a much lesser degree, maternal age are also factors when considering the risk of transmission of the premutation allele to a full mutation.Our findings demonstrate that a model with total CGG length, number of AGG interruptions, and maternal age is recommended for calculating the risk of expansion to a full mutation during maternal transmission. Taken together, the results of this study provide relevant information for the genetic counseling of female premutation carriers, and improve the current predictive models which calculate risk of expansion to a full mutation using only total CGG repeat length.

Dataset Information

Transcription-associated R-loop formation across the human FMR1 CGG-repeat region.

Publications

Transcription-associated R-loop formation across the human FMR1 CGG-repeat region.

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