Molecular evolution of the mammalian epiblast

Abstract

The mammalian pluripotent cell lasts for one day during in vivo development, but can be cultured in vitro to form embryonic stem (ES) cells which exhibit long-term self-renewal. This unique potential may have evolved in early mammals together with placental formation. Mutations in developmental genetic regulatory networks are likely important to evolution, thus I focused mainly on Oct4, uncovering new sequence information and identifying an Oct4 homolog in the platypus. 12 amino acid positions in the Oct4 DNA binding domain (DBD) are completely conserved within eutherians while differing in non-eutherians. I constructed Oct4 DBD VP16/EnR fusion proteins to observe gene expression differences, and full-length Oct4 chimeras to test their ability to induce pluripotency using the induced pluripotent stem cell (iPS) system. I show that there are only subtle cell-level differences between eutherian and platypus Oct4 DBDs, strongly suggesting that the pluripotent capability of Oct4 predates the appearance of eutherian mammals.