Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Genetics

First Advisor

Khokha, Mustafa

Abstract

Carbon metabolism is critical for complex multicellular life. Therefore, mitochondria, and the aerobic metabolism that they perform, have long been a focus of developmental biologists. The discovery of the Spemann-Mangold Organizer, a powerful embryonic patterning center in the dorsal region of the vertebrate embryo, first inspired the idea that embryonic patterning and aerobic metabolism may be connected almost 100 years ago. However, the advent of modern molecular genetics overshadowed this work, and metabolism in development has only recently resurfaced as a focus in the field. A permissive role for mitochondria has been well studied in development. However, it remains unclear whether a mechanism exists by which mitochondrial metabolism can instruct cell fate and embryonic patterning. Here, we demonstrate that mitochondrial oxidative metabolism regulates cell fate and patterning of the blastula via Hif-1α. Genetic disruption of the mitochondrial and patterning disease gene LRPPRC or exposure to hypoxia induces alteration in cell fates and expands the Spemann-Mangold Organizer, leading to downstream patterning defects of the heart and other tissues. Based on the hypoxia phenotype, we report that Hif-1α itself is sufficient to drive Organizer gene expression. Unexpectedly, oxygen consumption in the Organizer is 20% higher, rather than lower, than that of the ventral mesoderm, suggesting an increase in mitochondrial activity rather than regional hypoxia. We find that the increase in oxygen consumption is due to an inner mitochondrial membrane proton leak which decouples oxygen consumption from ATP production in the dorsal mesoderm. The proton leak is due to dorsal enrichment of the free c-subunit ring of F1Fo ATP synthase, which acts as an uncoupling channel to drive the increased rate of respiration. Overexpression of the free c-subunit is sufficient to induce Organizer cell fates via Hif-1α and can even induce a secondary, ectopic, body axis. Taken together, we have established that mitochondrial uncoupling in the dorsal mesoderm, driven by the ATP synthase free c-subunit, activates Hif-1α which determines the Spemann-Mangold Organizer, a tissue essential for global embryonic patterning.

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