| A small subset of mammalian genes are subject to imprinted regulation: these genes are expressed monoallelically, and in a parent-of-origin specific manner. The transcriptional states of these genes are determined during gametogenesis. Two of the best studied imprinted genes, H19 and Insulin-like growth factor 2 (Igf2) are closely-linked and reciprocally imprinted. The coordinate regulation of these genes has been shown to involve the binding of the vertebrate insulator protein, CTCF, to the maternally hypomethylated differentially methylated domain (DMD). However, the role CTCF has in maintaining the hypomethylated state of the DMD during oogenesis, a time when other methylation imprints are being established, is not yet understood. Using a transgenic-RNAi based approach to create oocytes with depleted levels of CTCF, we have examined the methylation state of the H19 DMD. Oocytes with a greater depletion of CTCF protein show acquisition of methylation specifically at the H19 DMD, suggesting that CTCF protects the H19 DMD from de novo methylation during oocyte growth. Furthermore, loss of CTCF protein causes maternal-effect lethality, in part due to arrest of embryos in early preimplantation stages. Together, our data show broad-ranging requirements for CTCF both in epigenetic gene regulation and in survival of the preimplantation embryo. |
