Conserved principles of the pluripotency and primordial germ cell gene regulatory networks: from basal vertebrates to mammals

Simpson, Luke Alexander (2022) Conserved principles of the pluripotency and primordial germ cell gene regulatory networks: from basal vertebrates to mammals. PhD thesis, University of Nottingham.

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Pluripotency defines the unlimited potential of cells in the primitive ectoderm of vertebrate embryos, from which all adult somatic cells and germ cells are derived. Understanding how the programming of pluripotency evolved has been obscured by the study of early development in models from lower vertebrates in which pluripotency is not conserved. Using Axolotl to model the development of the tetrapod ancestor, I examined the role of two transcription factors in early development associated with pluripotency in human embryonic stem cells (hESC), NANOG and ELK1.

In chapter three I investigated how the core pluripotency factor nanog programs pluripotency in axolotl development. Nanog marks the pluripotent domain in mammals and NANOG knockout results in the loss of pluripotency in vitro and the developmental arrest prior to the establishment of the epiblast in vivo. Here I show that in axolotl animal caps (AC), NANOG synergizes with NODAL activity and the epigenetic modifying enzyme DPY30 to direct the deposition of H3K4me3 in chromatin prior to the waves of transcription required for lineage commitment and developmental progression. I show that the interaction of NANOG and nodal with DPY30 is required to direct development downstream of pluripotency and this is conserved in axolotls and humans. These data also demonstrate that the interaction of NANOG and NODAL signaling represents the basal state of vertebrate pluripotency.

In chapter 4, I explored the role of ELK1 in germ layer formation and PGC specification in early development. ELK1 is a prototypical ETS domain transcription factor, conserved across metazoans and known to govern cell-fate decisions, acting downstream of fibroblast growth factor (FGF) signalling. ELK1 has also been identified as a factor essential to maintain the pluripotent state of hESC. Here I show that the lateral and intermediate mesoderm in axolotl embryos is diverted to somitic tissue in response to ELK1 knockdown, suggesting that the regulation of mesodermal differentiation by ELK1 may be conserved from amphibians to humans. Further, I uncover a novel role, showing that it is required for the formation of primordial germ cells (PGCs) in axolotl embryos. Together, these results establish ELK1 as a central player in the evolution of vertebrate mesoderm. Moreover, they align with the concept that as mechanisms of PGC specification evolve they can lead to fundamental changes in somatic development.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Loose, Matt
Alberio, Ramiro
Keywords: Pluripotency, Primordial germ cell, Gene regulatory networks, Basal vertebrates, Mammals
Subjects: Q Science > QH Natural history. Biology > QH426 Genetics
Q Science > QL Zoology > QL951 Embryology
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 69858
Depositing User: Simpson, Luke
Date Deposited: 31 Dec 2022 04:40
Last Modified: 31 Dec 2022 04:40

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