Metabolic Patterning and Regulation During Early Embryo Development and Appendage Regeneration

Abstract

Similarities have been drawn between both early embryos and regenerating tissues/ appendages. It is thought from many standpoints, such as signaling and patterning that tissue regeneration may recapitulate various processes that occur during initial development. Both early embryos and regenerating tissues require mass coordination of biological processes to achieve rapid proliferation. These high levels of proliferation may be achieved via regulation of cellular metabolism in a manner similar to the Warburg effect observed in cancer cells. Additionally these highly proliferative systems both demonstrate a requirement for a sustained increase in reactive oxygen species (ROS). ROS has previously been demonstrated to interact and regulate cell cycle machinery, thus potentially controlling the rate of proliferation. The overarching question of this thesis was; to what extent do the processes of early embryonic development and tissue regeneration share or differ in metabolic states and how are these regulated? By studying both metabolic and ROS profiles in early embryos of X. laevis, I uncovered a novel coupled oscillation system that works to regulate the cell cycle. ATP and ROS levels were found to rise and fall once per cell cycle in an inverse manner. Analysis of the metabolic oscillations suggested that the metabolic profile of early embryos was switching between a Warburg-like to a non-Warburg like metabolism. The metabolic switching directly led to oscillations in the mitochondrial production of ROS. While ROS was found to feedback on a key metabolic enzyme PKM2 to facilitate the metabolic switching, it also affected the cell cycle. In the model I have generated from these data, during the non-Warburg phase of the cell cycle both glycolysis and OXPHOS are active which lead to high ATP levels. This generated low ROS levels, which were not sufficient to inactivate a key cell cycle regulator, thus leading to an active Cyclin B-Cdk1 complex to allow entry into mitosis. As the cell approached mitotic exit and into interphase, a Warburg-like metabolism dominated in the embryo, whereby only glycolysis remained highly active. The down regulation of OXPHOS allowed higher levels of ROS to be produced, which indirectly inactivated the Cyclin B-Cdk1 complex allowing the cell cycle transition. Therefore, this coupled oscillation system can regulate the timing of cell cycle leading to the rapid proliferation required in early embryos. If it is unveiled that this mechanism is an archetype for systems of rapid proliferation, this will change the way we investigate regenerating tissues and attempt to recreate a pro-regenerative phenotype.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Royston Goodacre (Supervisor) & Enrique Amaya (Supervisor)