Evaluation in mammalian oocytes of gene transcripts linked to epigenetic reprogramming

Abstract

The mature mammalian metaphase II (MII) oocyte has a unique ability to reprogram sperm chromatin and support early embryonic development. This feature even extends to the epigenetic reprogramming of a terminally differentiated cell nucleus as observed in connection with somatic cell nuclear transfer. Epigenetic nuclear reprogramming is highly linked to chromatin structure and includes covalent modifications of DNA and core histone proteins as well as reorganization of higher-order chromatin structure. A group of conserved enzymes mediating DNA methylation, methyl-CpG-binding protein (MeCP), histone acetylation and methylation, and chromatin remodeling are extensively involved in epigenetic reprogramming in mammalian cells. Using the oligonucleotide microarray technique, the present study compared the expression levels of 86 genes associated with epigenetic reprogramming in murine in vivo matured MII oocytes with that of germinal vesicle oocytes. Correlation between biological replicates was high. A total of 57 genes with potential reprogramming effect were detected. In MII oocytes, four genes were significant up-regulated, whereas 18 were down-regulated and 35 unchanged. The significantly regulated genes were validated by real-time quantitative RT-PCR. For example, MII oocytes showed a significant down-regulation of oocytespecific maintenance DNA methyltransferase, Dnmt1o, and up-regulation of MeCP transcript, methyl-CpG binding domain protein 2. Furthermore, histone acetyltransferases were proportionally overrepresented when compared with histone deacetylases. These data elucidate for the first time some of the mechanisms that the oocyte may employ to reprogram a foreign genome either in form of a spermatozoa or a somatic nucleus and may thus be of importance for advancing the fields of stem cell research and regenerative medicine.

MLL2 Is Required in Oocytes for Bulk Histone 3 Lysine 4 Trimethylation and Transcriptional Silencing

“…Ccnb1ip/Hei10 expression was significantly decreased in Mll2 Gdf9 cKO oocytes ( p <0.05; Table 1). Interestingly, expression of the histone 4 acetylase Kat5/Tip60 (Lysine acetyltransferase 5), which has been previously reported to be present in oocytes, was significantly increased in Mll2 Gdf9 cKO oocytes (Table 1, p <0.05) [65] and may therefore contribute to the observed increase in H4K12 acetylation.…”

Histone modifications during mammalian oocyte maturation: Dynamics, regulation and functions

“…41 Remarkably, accompanying with meiotic maturation, the relative abundance of SUV39H1 dramatically decreased in mouse and bovine oocyte. 69,70 G9A transcripts were absent in immature and matured mouse oocytes 70 and downregulated in bovine oocytes. 41,69 PcG proteins enhancer of zeste2 (EZH2) is one of HMTs responsible for methylating H3/K27.…”

Maternal age effect on mouse oocytes: new biological insight from proteomic analysis

“…Similar to other studies, cDNA was synthesized using mRNAspecific poly(dT) primers binding the poly(A) tail of mRNA (Hamatani et al 2004, Kocabas et al 2006. It is possible that amplification with poly(dT) primers distorts the representation of the original mRNA population by amplifying preferentially those mRNAs that have a longer poly(A) tail instead of those mRNAs with short or no poly(A) tail (Oliveri et al 2007). However, the use of poly(dT) primers ensures that only those transcripts are amplified that are amenable to translation at the time of sampling.…”