In mammals, the ability to regulate transcription is absent at the start of life. This fundamental ability is acquired during early cleavage stages through the formation of a transcriptionally repressive chromatin state (TRCS), wherein transcriptional enhancers first become necessary. Establishing the TRCS soon after fertilization is vital for two reasons: 1) it is important to suppress activation of endogenous transposable elements, which if activated can be mutagenic, and 2) it is essential to correctly execute the correct transcriptional program for embryo viability. This includes activating and repressing thousands of genes during four successive waves of embryonic genome activation (EGA1 to 4). Failure to establish the TRCS and to regulate EGA waves correctly kills embryos. We discovered that Structural maintenance of chromosomes flexible hinge domain containing protein one (SMCHD1) is a maternal effect gene that potentially orchestrates all of these events. SMCHD1 1) promotes EGA1 termination, 2) is implicated in repressing genes that are up-regulated during EGA2 to 4, and 3) supports inner cell mass (ICM) formation and embryo viability revealing long-term impacts of early SMCHD1 actions. Our overall model is that oocyte-expressed SMCHD1 terminates EGA1 and helps to establish the TRCS to allow correct gene regulation during EGA2. Embryo-expressed SMCHD1 then maintains and extends gene repression and enables optimum control of EGA3 & EGA4 necessary for embryo viability. The study of SMCHD1 mechanisms of action thus provides an important new entry for discovering fundamental mechanisms regulating embryonic genome function and viability. We created a novel floxed Smchd1 allele, which can be used to achieve oocyte-specific ablation of SMCHD1 function, and thus create embryos that lack maternal, embryonic or both sources of SMCHD1, as needed to dissect SMCHD1 earl functions. This proposal will provide essential preliminary data on the phenotype of these knockout animals to allow more in-depth mechanistic studies to be pursued.
In Aim 1 we will determine the effects of oocyte-specific knockout on oogenesis and early embryo viability.
In Aim 2 we will assess SMCHD1?s role in controlling genes that are activated during the first two waves of gene expression during the 2-cell stage. Overall, this project seeks to solve long-standing fundamental mysteries of how mammalian embryos become competent for life.
This project will break new grounding understanding fundamental processes that enable mammalian embryos to survive. The project focuses on the roles of SMCHD1, a broadly acting repressor of gene expression, in establishing the capacity for early embryo to regulate their gene expression correctly. This project seeks to solve long-standing fundamental mysteries of how mammalian embryos become competent for life.
