Figure 3. The maternal transcriptome degradation is regulated by decay pathways controlled by two transcriptional initiation machineries.

Two initiation machinery switches occur in the life time of the maternal transcriptome: at the beginning of oocyte growth and at the zygotic genome activation (ZGA) after fertilization. The bulk of the maternal transcriptome is produced by transcription initiated by the TBPL2/TFIIA complex (blue) that interacts preferentially with TATA boxes (TATA) of core promoters with sharp promoter architecture. Active RNA decay during this phase has been recently suggested [26], probably controlled by TBPL2/TFIIA initiated transcripts (blue line). After growth, transcription is silent and the different phases of maternal transcriptome degradation are under the control of proteins translated from dormant transcripts transcribed during the oocyte growth (dashed blue line). After ZGA, the degradation of the maternal transcriptome is reinforced by zygotically expressed proteins (orange line), leading to the disappearance of the maternal transcriptome after the four-cell stage. An interesting hypothesis is that a similar complete degradation of the initial transcriptome inherited from the TFIID/TBP transcription initiation occurs during oocyte growth (question mark). Note that there is an available resource on transcripts dynamics during maternal to zygotic transition [93].