A new paradigm for genomic imprinting

Development of embryos depends on mothers in many organisms. This is the case in viviparous animals but also in liverworts which are relative of mosses. We discovered that the liverwort Marchantia represses the paternal chromosomes in the embryo. Hence, the embryo development depends primarily on the expression of the maternal genes. This paternal chromosome repression (PCR) is mediated by the deposition of the repressive modification of histone H3 -H3K27me3, which is an epigenetic mark maintained through cell division. This proposal is dedicated to find the mechanisms that install PCR and how PCR breaks down. We will use biochemistry and genetics to find the process that cause silencing of the paternal genome before its fusion with the maternal genome at fertilization. We will explore how a protein that binds to the repressive epigenetic mark is involved in the maintenance of PCR through spatial segregation and compaction of the paternal genome. We will identify the regulation of this protein that cause the breakdown of PCR at the end of embryogenesis. The study of PCR will expand our mechanistic understanding of epigenetic repression and provide cues to find similar mechanisms in viviparous animals. 1