Biomedical subjects

Mercedes G Bermúdez

Publications and source records attributed to Mercedes G Bermúdez.

4 recordsLinked to original sources

PubMed2005

Association of abnormal morphology and altered gene expression in human preimplantation embryos.

OBJECTIVE: We set out to characterize the expression of nine genes in human preimplantation embryos and determine whether abnormal morphology is associated with altered gene activity. DESIGN: Reverse transcription and real-time polymerase chain reaction were used to quantify the expression of multiple genes in each embryo. The genes studied have various important cellular roles (e.g., cell cycle regulation, DNA repair, and apoptosis). SETTING: Research laboratory working closely with a clinical IVF practice. PATIENT(S): Over 50 embryos were donated by infertile patients (various etiologies). Among these, all major stages of preimplantation development and a variety of common morphologic abnormalities were represented. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Quantification of mRNA transcripts. RESULT(S): We detected an association between certain forms of abnormal morphology and disturbances of gene activity. Cellular fragmentation was associated with altered expression of several genes, including TP53, suggesting that fragmenting blastomeres are suffering stress of a type monitored by p53, possibly as a consequence of suboptimal culture conditions. CONCLUSION(S): Appropriate gene expression is vital for the regulation of metabolic pathways and key developmental events. Our data indicates a possible causal relationship between changes in gene expression and the formation of clinically relevant abnormal embryo morphologies. We hypothesize that embryos with expression profiles characteristic of good morphology and appropriate for their developmental stage have the greatest potential for implantation. If confirmed, this could lead to a new generation of preimplantation genetic diagnosis (PGD) tests for assessing embryo viability and predicting implantation potential.

Blastocyst↗

PubMed2004

Reliability of comparative genomic hybridization to detect chromosome abnormalities in first polar bodies and metaphase II oocytes.

BACKGROUND: Preimplantation Genetic Diagnosis (PGD) using FISH to analyze up to nine chromosomes to discard chromosomally abnormal embryos has resulted in an increase of pregnancy rates in certain groups of patients. However, the number of chromosomes that can be analyzed is a clear limitation. We evaluate the reliability of using comparative genomic hybridization (CGH) to detect the whole set of chromosomes, as an alternative to PGD using FISH. METHODS AND RESULTS: We have analysed by CGH both, first polar bodies (1PBs) and metaphase II (MII) oocytes from 30 oocytes donated by 24 women. The aneuploidy rate was 48%. Considering two maternal age groups, a higher number of chromosome abnormalities were detected in the older group of oocytes (23% versus 75%, P < 0.02). About 33% of the 1PB-MII oocyte doublets diagnosed as aneuploid by CGH would have been misdiagnosed as normal if FISH with nine chromosome probes had been used. CONCLUSION: We demonstrate the reliability of 1PB analysis by CGH, to detect almost any chromosome abnormality in oocytes as well as unbalanced segregations of maternal translocations in a time frame compatible with regular in vitro fertilization (IVF). The selection of euploid oocytes could help to increase implantation and pregnancy rates of patients undergoing IVF treatment.

Adult↗

PubMed2004

Expression profiles of individual human oocytes using microarray technology.

Microarray technology is a relatively new technique that provides the investigator with the ability to monitor and quantify the expression of thousands of genes simultaneously. This technological breakthrough has the potential to provide detailed insight into cellular processes involved in the regulation of gene expression. In this study, microarray methods were used to examine the expression of linearly amplified RNA from individual and pooled (n = 5) human oocytes. The amplification strategy consistently produced a complex representative cDNA population. A catalogue of 1361 transcripts expressed in human oocytes was identified, of which 406 have been independently confirmed using other methods.

DNA, Complementary↗

PubMed2003

Detailed investigation of factors influencing amplification efficiency and allele drop-out in single cell PCR: implications for preimplantation genetic diagnosis.

Preimplantation genetic diagnosis (PGD) of single gene disorders relies on PCR-based tests performed on single cells (polar bodies or blastomeres). Despite the use of increasingly robust protocols, allele drop-out (ADO; the failure to amplify one of the two alleles in a heterozygous cell) remains a significant problem for diagnosis using single cell PCR. In extreme cases ADO can affect >40% of amplifications and has already caused several PGD misdiagnoses. We suggest that an improved understanding of the origins of ADO will allow development of more reliable PCR assays. In this study we carefully varied reaction conditions in >3000 single cell amplifications, allowing factors influencing ADO rates to be identified. ADO was found to be affected by amplicon size, amount of DNA degradation, freezing and thawing, the PCR programme, and the number of cells simultaneously amplified. Factors found to have little or no affect on ADO were local DNA sequence, denaturing temperature (94 or 96 degrees C) and cell type. Consideration of the causal factors identified during this study should permit the design of PGD protocols that experience little ADO, thus improving the accuracy of PGD for single gene disorders.

Alleles↗