Exploring the role of early transcription on the zygotic genome activation in the zebrafish embryo

Woźniak, Kacper Tomasz (2023). Exploring the role of early transcription on the zygotic genome activation in the zebrafish embryo. University of Birmingham. Ph.D.

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Abstract

Early embryos are transcriptionally quiescent and rely on the signals provided by the mother to guide them through the first hours of development. Through the process of zygotic genome activation, embryos are reprogrammed from a fully differentiated egg cell into totipotent stem cells. This corresponds with a vast transcriptional activation event in the embryo, as transcription of zygotic genes is activated. However, some genes are able to escape the transcriptional silencing before zygotic genome activation, forming an early wave of transcription. In this thesis, I have aimed to utilise a teleost model organism, Danio rerio (zebrafish), to investigate the role of one such early wave transcription factor, mxtx2, in zygotic genome activation. I have aimed to characterise the role of mxtx2 by generating a loss of function and null mutants of its gene. Additionally, I have aimed to characterise cell cycle and genome activation dynamics in the first distinct extra-embryonic tissue of the embryo – the yolk syncytial layer – induction of which is mediated by mxtx2. In this thesis, I demonstrate the generation of an efficient method of mosaic loss of function of mxtx2 by Cas9 nuclease. I have shown that mxtx2 phenotype generated by this loss of function phenocopies previous studies, independently confirming the results. I also demonstrate a previously unreported phenotype caused by Cas13d nuclease, causing unspecific developmental abnormalities and embryonic lethality. The exploration of cell cycle and transcription dynamics in the zebrafish embryo provided evidence showing a specific cell cycle and transcriptional delay in the nuclei of the yolk syncytial layer, which we hypothesise is caused by a delay in zygotic genome activation in the yolk syncytial layer. Aided with further studies, this could provide the first evidence in any organism of distinct zygotic genome activation control in subsets of embryonic cells.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):