This project has been the focus of my PhD over the last four years and I couldn’t have done it without the support of my co-authors, especially Marco Stock and Eva Hörmanseder, and many others. A huge thank you to all who contributed to this work!
@marcostock.bsky.social @evahoermanseder.bsky.social

Finally, we identify that H3K4 methyltransferases Kmt2b and Cxxc1 are key players in ensuring H3K4 methylation-mediated transcriptional memory in these early, transcriptionally silent embryos.

Notably, by depleting H3K4 methylation specifically in the transcriptionally silent window before ZGA, we show that maintenance of H3K4 methylation patterning in pre-ZGA embryos is crucial for proper ZGA and expression of pluripotency factors.

We correlated this with distinct configurations of chromatin accessibility, DNA methylation and GC content, explored for the first time in Xenopus pre-ZGA embryos!

Also, we found that H3K4me3 is mostly maintained from gametes to embryos, separated by a transcriptionally silent phase. Surprisingly, this maintenance was at promoters of genes that were transcribed in the gametes and are activated again during ZGA in the embryo.

Active histone modifications, such as H3K4me3, have long been thought to be dependent on transcription factor binding and active gene transcription. Despite this, we show that H3K4me3 can be found in non-transcribing and fast-replicating Xenopus embryos before zygotic genome activation (ZGA).