Epigenetic Reprogramming in Chick Primordial Germ Cells

Abstract

The germline refers to a population of cells within the body of an organism that can potentially pass on genetic information to the next generation through reproduction. In mammals, the germline must be reprogrammed from somatic cells at each generation because it is not a continuous cellular lineage. During this cellular reprogramming process, upon migration to the gonadal anlagen, primordial germ cells undergo drastic genome-wide DNA demethylation. This DNA demethylation may be essential for PGCs to attain the additional developmental potency required to become the germline. In contrast, other vertebrates do not reprogramme the germline from soma each generation and instead possess an immortal germline, preformed by maternal germplasm carried through from egg. The aim of this project was to compare global methylation levels between chick PGCs at developmental timepoints analogous to where epigenetic reprograming has been observed in mammals and somatic tissues, with the ultimate goal of identifying the presence or absence of genome-wide epigenetic reprogramming in a non-mammalian vertebrate with a preformed germline. I developed a protocol for extracting embryos from developmental ages ranging from embryonic day 2.5-7 (E2.5-7) and subsequently purified PGCs from these samples. Following this, an optimised method for genome epigenome quantification known as post-bisulfite adapter tagging (PBAT) was utilised to determine the global methylation profiles of each sample. No significant reduction in global CG methylation was observed between SSEA1 positive primordial germ cells and control cells. Although there could be confounding technical issues, no evidence was found to suggest that genome-wide reprogramming occurs in chickens.