Function of Kdm4dl-mediated heterochromatin removal in the preimplantation mouse embryo

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PROJECT ABSTRACT This project will investigate the function of a currently unstudied histone demethylase, Kdm4dl, in the mouse preimplantation embryo. Many others have shown the developmental importance of activating genes and repeat sequences during a process known as Embryonic Genome Activation (EGA), the moment when the embryo switches on transcription for the first time. EGA involves activation of both protein coding genes as well as repeat sequences that are critical for remodeling the chromatin environment of the early embryo. Yet, even with its known developmental importance, the factors which facilitate EGA are still largely unknown. Here, for the first time, I will investigate the importance of Kdm4dl, which catalytically removes the repressive histone modification H3 Lysine 9 tri-methylation (H3K9me3), in early mouse embryogenesis. I hypothesize that Kdm4dl is required for reprogramming the nuclei of the preimplantation embryo by removing repressive H3K9me3, which facilitates strong activation of EGA-associated transcripts. In line with this hypothesis, my preliminary data demonstrate temporally coordinated Kdm4dl protein expression during the 2-cell stage, when EGA occurs. Moreover, Kdm4dl over-expression is sufficient to demethylate H3K9me3 in embryonic stem cells leading to strong activation of EGA-associate transcripts and repeats. Combined, these preliminary data provide further support for pursuing the project’s hypothesis further. The two outstanding questions I aim to address are: 1. Is Kdm4dl expression sufficient to reprogram cells to a state of expanded potential, consistent with a 2-cell-like totipotent state? and 2. Is Kdm4dl expression necessary for H3K9 demethylation and activation of EGA-associated genes and repeats in vivo? To aid in addressing these questions, I have developed both an innovative embryonic stem cell system which recapitulates the temporal dynamics of Kdm4dl expression in the preimplantation embryo, and I have also established a Kdm4dl knockout mouse model. This research project, combined with my detailed training plan, is consistent with my technical and professional goals of becoming an independent academic investigator studying chromatin dynamics in the early mammalian embryo, with relevance to human fertility.