TFIIH is highly dynamic during zygotic genome activation in Drosophila and its depletion causes catastrophic mitosis

In Drosophila zygotic genome activation occurs in pre-blastoderm embryos during rapid mitotic divisions. How the transcription machinery is coordinated to achieve this goal in a very brief time span is still poorly understood. TFIIH is fundamental for transcription initiation by RNA polymerase II (RNAPII). Herein, we show the in vivo dynamics of TFIIH at the onset of transcription in Drosophila embryos. TFIIH shows an oscillatory behaviour between the nucleus and cytoplasm. TFIIH foci are observed from interphase to metaphase, and co-localize with the RNAPII phosphorylated at serine 5 (RNAPIIS5P) at prophase, suggesting that transcription overlaps with the first mitotic phases. Furthermore, embryos with defects in subunits of either the CAK or the core subcomplexes of TFIIH show catastrophic mitosis. Although, transcriptome analyses show altered expression of several maternal genes that participate in mitosis, the global level of RNAPIIS5P in TFIIH mutant embryos is similar to wild type, therefore, a direct role for TFIIH in mitosis cannot be ruled out. These results provide important insights regarding the role of a basal transcription machinery component when the zygotic genome is activated.