Search

The levels of genomic DNA methylation in vertebrate species display a wide range of developmental dynamics. Here, we show that in contrast to mice, the paternal genome of the amphibian, Xenopus laevis, is not subjected to active demethylation of 5-methyl cytosine immediately after fertilization. High levels of methylation in the DNA of both oocyte and sperm are maintained in the early embryo but progressively decline during the cleavage stages. As a result, the Xenopus genome has its lowest methylation content at the midblastula transition (MBT) and during subsequent gastrulation. Between blastula and gastrula stages, we detect a loss of methylation at individual Xenopus gene promoters (TFIIIA, Xbra, and c-Myc II) that are activated at MBT. No changes are observed in the methylation patterns of repeated sequences, genes that are inactive at MBT, or in the coding regions of individual genes. In embryos that are depleted of the maintenance methyltransferase enzyme (xDnmt1), these developmentally programmed changes in promoter methylation are disrupted, which may account for the altered patterns of gene expression that occur in these embryos. Our results suggest that DNA methylation has a role in regulating the timing of gene activation at MBT in Xenopus laevis embryos. Key Words: Xenopus; development; demethylation; xDnmt1.

Evaluates the hypothesis that vertebrate cells possess mechanisms that protect them from epigenomic stress similar to DNA damage checkpoints. Effect of DNA methyltransferase knockdown by an oligonucleotide antisense on the intra-S-phase arrest of DNA replication; Implication on the arrest of cells at different positions throughout the S-phase of the cell cycle; Proposition on intra-S-phase arrest of DNA replication.

: Objective:To determine the relationship between sperm DNA methylation level and sperm characteristics and pregnancy rates.: Design:Prospective study. Quantitation by image analysis of DNA methylation in sperm nucleus.: Setting:Department of Reproduction Biology, Edouard Herriot Hospital, Lyon, France.: Patient(s):Infertile couples undergoing IVF-ET.: Intervention(s):The immunostaining of 5 methyl-cytosine was performed on the spare sperm suspension that was used for an assisted reproduction technology procedure.: Main outcome measure(s):Sperm characteristics according to World Health Organization criteria, sperm motility parameters with computer-assisted semen analysis, sperm DNA methylation level, and heterogeneity index (HI).: Result(s):Sperm DNA methylation level and HI are correlated with sperm DNA characteristics. HI is negatively correlated with fertilization rate; sperm DNA methylation level is correlated with pregnancy rate.: Conclusion(s):The DNA methylation level in human spermatozoa could be a new approach to evaluating the ability of spermatozoa to fertilize and lead to normal embryo development. [Copyright &y& Elsevier]