Epigenetic reprogramming occurs during oocyte growth in mice, a stage where a number of important events are occurring, including transcription of maternal mRNAs for storage in the mature egg, global transcriptional silencing an the acquisition of meiotic competence. Oocyte growth occurs in conjunction with follicular development over a period of many days. The signals involved in initiating different stages in oocyte and follicular development and the concurrent epigenetic changes are poorly understood. Here we examine the role of stern cell factor (SCF or Kit ligand) on the early- to mid-stages of oocyte growth and on DNA methyltransferase expression and function using a one-step in vitro culture system. Our results show that SCF promotes early oocyte growth and development to the multilaminar follicle stage. Oocyte growth is Sufficient to trigger transcription of Dnmt 1 and Dnmt3L from dedicated oocyte promoters, and we show that eggs undergoing growth in the absence of follicle development in Foxo3 mutants show elevated levels of Dnmt1. The methyltransferase proteins undergo sequential relocalisation in the oocyte, with DNMT1 being exported from the nucleus at the bilaminar follicle stage, while DNMT3A is transported into the nucleus at the multi laminar stage, indicating an important role for trafficking in controlling imprinting. SCF is thought to signal partly through the phophostidylinositol 3 (P13) kinase pathway: inhibiting this path was previously shown to prevent FOXO3 nuclear export and we could show here that it also prevented DNMT1 export. Some oocytes reached full size (70 mu M) in this in vitro system, but no secondary follicles were formed, most likely due to failure of the thecal layer to form properly. De novo methylation of imprinted genes was seen in some oocyte Cultures, with methylation levels being highest for Snrpn and lgf2r which are methylated early in vivo, while Peg1, which is methylated late, showed little or no methylation. SCF treatment did not increase the number of cultures showing methylation. We saw no evidence for de novo methylation of IAP repeats in our Cultures, These results suggest that while methyltransferase loading is triggered by oocyte growth, in which SCF plays an important role, complete methylation probably requires progression to the secondary follicle stage and is unlikely to be affected by SCF.

Lees Murdock, D., Lau, H., Castrillon, D., DE FELICI, M., Walsh, C. (2008). DNA methyltransferase loading, but not de novo methylation, is an oocyte-autonomous process stimulated by SCF signalling. DEVELOPMENTAL BIOLOGY, 321(1), 238-250 [10.1016/j.ydbio.2008.06.024].

DNA methyltransferase loading, but not de novo methylation, is an oocyte-autonomous process stimulated by SCF signalling

DE FELICI, MASSIMO;
2008-01-01

Abstract

Epigenetic reprogramming occurs during oocyte growth in mice, a stage where a number of important events are occurring, including transcription of maternal mRNAs for storage in the mature egg, global transcriptional silencing an the acquisition of meiotic competence. Oocyte growth occurs in conjunction with follicular development over a period of many days. The signals involved in initiating different stages in oocyte and follicular development and the concurrent epigenetic changes are poorly understood. Here we examine the role of stern cell factor (SCF or Kit ligand) on the early- to mid-stages of oocyte growth and on DNA methyltransferase expression and function using a one-step in vitro culture system. Our results show that SCF promotes early oocyte growth and development to the multilaminar follicle stage. Oocyte growth is Sufficient to trigger transcription of Dnmt 1 and Dnmt3L from dedicated oocyte promoters, and we show that eggs undergoing growth in the absence of follicle development in Foxo3 mutants show elevated levels of Dnmt1. The methyltransferase proteins undergo sequential relocalisation in the oocyte, with DNMT1 being exported from the nucleus at the bilaminar follicle stage, while DNMT3A is transported into the nucleus at the multi laminar stage, indicating an important role for trafficking in controlling imprinting. SCF is thought to signal partly through the phophostidylinositol 3 (P13) kinase pathway: inhibiting this path was previously shown to prevent FOXO3 nuclear export and we could show here that it also prevented DNMT1 export. Some oocytes reached full size (70 mu M) in this in vitro system, but no secondary follicles were formed, most likely due to failure of the thecal layer to form properly. De novo methylation of imprinted genes was seen in some oocyte Cultures, with methylation levels being highest for Snrpn and lgf2r which are methylated early in vivo, while Peg1, which is methylated late, showed little or no methylation. SCF treatment did not increase the number of cultures showing methylation. We saw no evidence for de novo methylation of IAP repeats in our Cultures, These results suggest that while methyltransferase loading is triggered by oocyte growth, in which SCF plays an important role, complete methylation probably requires progression to the secondary follicle stage and is unlikely to be affected by SCF.
2008
Pubblicato
Rilevanza internazionale
Articolo
Sì, ma tipo non specificato
Settore BIO/11 - BIOLOGIA MOLECOLARE
English
Con Impact Factor ISI
Dnmt1; Dnmt3A; Dnmt3B; Dnmt3L; follicle; Foxo3; IAP; oocyte growth; SCF; snrpnDNA methyltransferase; DNA methyltransferase 1; DNA methyltransferase 3A; growth factor; stem cell factor; animal experiment; article; autonomic innervation; dnmt1 gene; dnmt3l gene; embryo; epigenetics; foxo3 gene; genetic transcription; genome imprinting; methylation; mouse; mutant; nonhuman; oocyte development; ovary follicle; priority journal; protein transport; signal transduction; animals; DNA (Cytosine-5-)-Methyltransferase; DNA methylation; female; growth hormone; inhibitor of apoptosis proteins; ogenesis; ovarian follicle; signal transduction
Lees Murdock, D., Lau, H., Castrillon, D., DE FELICI, M., Walsh, C. (2008). DNA methyltransferase loading, but not de novo methylation, is an oocyte-autonomous process stimulated by SCF signalling. DEVELOPMENTAL BIOLOGY, 321(1), 238-250 [10.1016/j.ydbio.2008.06.024].
Lees Murdock, D; Lau, H; Castrillon, D; DE FELICI, M; Walsh, C
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/8114
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