Figure 1. Establishment and reshaping of the maternal transcriptome in the mouse.

(A) Summary of the folliculogenesis and early development in the mouse. Each follicle (from primordial to pre-ovulatory) contains a single primary oocyte arrested at the end of prophase I. Oocyte growth occurs from the primary to the pre-antral follicle stages in a 3-weeks period. Oocyte maturation leads to the resumption of meiosis and ovulation of a secondary oocyte arrested in metaphase II. Meiosis II is completed upon fertilization. Zygotic genome activation (ZGA) is initiated in late 1-cell embryo and complete in 2-cell embryo stages. The indicative timing of folliculogenesis is indicated below [15]. dpp, days post partum. (B) Dynamic expression of TBP (blue) and TBPL2 (pink) proteins. While both TBP and TBPL2 proteins are present in primordial follicle oocytes, TBP is not present during oocyte growth, being replaced by TBPL2. After oocyte growth, TBPL2 protein is not detected anymore. Only TBP protein reappears after fertilization. (C) Evolution of the maternal transcriptome (beige). Oocyte growth is characterized by an important increase in RNA polymerase II transcription activity (red curve) driven by the TBPL2 machinery. Transcription ceases after oocyte growth and remains silent until ZGA. A major reshaping of the maternal transcriptome begins with oocyte maturation by maternally controlled mRNA decay (green curve) degrading 50% of the transcripts, while only 30% remain at fertilization. The degradation is reinforced after ZGA by embryonically controlled mRNA decay products (blue curve).