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Introduction
Several studies have indicated that a dynamic alteration in transcriptional activity and gene expression regulation occurs during oogenesis and early development. A growing mouse oocyte transcribes many specific genes, e.g. zp3 and dnmt10 (Doherty et al ., 2002; Howell et al ., 2001; Soyal et al ., 2000). However, when the oocyte is almost full sized, transcription stops via an unknown mechanism and a transcriptionally inert state is maintained during meiosis. Fertilization triggers the completion of meiosis and the initiation of transcription by the zygotic genome in 1-cell embryos. In the male pronucleus (PN), the chromatin structure is not repressed, which allows enhancer-independent transcription from a microinjected reporter gene (Majumder et al ., 1993). Transcriptional regulation is altered markedly during the 2-cell stage. In embryos at the late 2-cell stage, promoter activity is repressed and an enhancer is necessary for transcription. A TATA-less promoter is utilized at this stage, but not in growing oocytes (Nothias et al ., 1995). At the blastocyst stage, the TATA-less promoter becomes more active. These dramatic changes in transcriptional regulation imply a global shift in the gene expression profile (Hamatani et al ., 2004; Wang et al ., 2004), which is probably regulated by alterations in epigenetic factors, such as transcription factors (TFs).
Although general transcription factors such as Sp1 and TBP are expressed ubiquitously and play basic roles in transcription, most other TFs are expressed and active in specific types of cells at a specific stage during proliferation and differentiation. For example, the cAMP response-element modulator is expressed in the testis and is essential for inducing the expression of testis-specific genes (Kotaja et al ., 2004; Krausz & Sassone-Corsi, 2005). Furthermore, recent studies have revealed that some transcription factors are sufficient to create specific cell characteristics, e.g. HES in neurocytes, Oct3/4 in germ cells and MyoD in muscular cells (Brand-Saberi, 2005; Johnson et al ., 2004; Kageyama et al ., 2005; Nichols et al ., 1998; Tanaka et al ., 2002). Our objective was to determine which transcription factors are expressed and responsible for specific cell characteristics at each stage of oogenesis and preimplantation development. Such knowledge about the expression of specific TFs would be useful in understanding gene expression regulation during oogenesis and preimplantation development. However,...