Functions of Genomic Hypomethylation in Gametogenesis

Introduction

Replication in S phase duplicates not only the genome but also the epigenome, to ensure cell identity is propagated and genome stability maintained in daughter cells. Epigenome propagation in development has been understudied due to lack of appropriate methods, even though replication is widely accepted to be a primary vehicle through which programmed epigenetic changes occur in vivo.

Germline Development

In mammalian germline development, the epigenome is reprogrammed via impairment of the epigenome maintenance network. By dividing without maintaining core components of the epigenome, primordial germ cells harbor genomes devoid of the crucial repressive mark DNA methylation.

Consequences of Hypomethylation

Hypomethylation is destabilizing because it de-represses transposable elements. Despite this, oocytes arrest in a hypomethylated state, regaining methylation only in preparation for ovulation as part of puberty. In parallel, two-thirds of the oocyte pool dies around birth in mammals, and the features delineating oocytes that survive this process from those that die are unclear.

Hypothesis

I propose that hypomethylation is alternately selected for and against across gametogenesis. Specifically, that hypomethylation is a positive feature in primordial germ cells but a deleterious feature in the female germline after sex specification.

Methodology

To test this, we will develop novel transgenic mouse models and technologies to study epigenome propagation in vivo. We will utilize:

1. State-of-the-art sequencing
2. Mass spectrometry
3. Microscopy
4. Metabolic labeling approaches

By developing a method for tracking DNA molecules and their associated methyl marks across division in live animals and embryos, we will establish an unprecedented technology for understanding epigenome propagation in development.

Expected Outcomes

Cumulatively, this work will uncover the functions and consequences of global hypomethylation in the germline, and provide groundbreaking insights into the nature of mitotic and intergenerational epigenetic inheritance in vivo.