PGC reversion to pluripotency involves erasure of DNA methylation from imprinting control centers followed by locus-specific re-methylation

Primordial germ cells (PGCs) are fate restricted to differentiate into gametes in vivo. However when removed from their embryonic niche PGCs undergo reversion to generate pluripotent embryonic germ cells (EGCs) in vitro. One of the major differences between EGCs and embryonic stem cells (ESCs) involves variable methylation at imprinting control centers (ICCs), a phenomenon that is poorly understood. In the current study we show that reverting PGCs to EGCs involves ICC methylation erasure, which remain stably hypomethylated at Snrpn, Igf2r and Kcnqot1. In contrast, the H19/Igf2 ICC undergoes almost complete de novo remethylation. Using the same approach for PGCs differentiated in vitro from ESCs we show that the Snrpn ICC is erased however the hypomethylated state is highly unstable. We also discovered that when the H19/Igf2 ICC is abnormally hypermethylated in ESCs, ICC methylation is not erased with differentiation into PGCs. This highlights the importance of not only launching germline differentiation with correctly methylated ESC lines but also the need to better stabilize the hypomethylated state in the in vitro derivatives following ICC erasure. Overall design: RNA seq of E9.5 PGCs, iPGCs, PGCLCs and EGCs using small cell numbers from start. N=2 biological replicates in 2 technical sequencing replicates.

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Oliveros-Etter M, Li Z, Nee K, Hosohama L, Hargan-Calvopina J, Lee SA, Joti P, Yu J, Clark AT