The dynamics of Ca2+ and ATP in mammalian eggs during fertilization and artificial egg activation

Aliyev, Elnur 2025. The dynamics of Ca2+ and ATP in mammalian eggs during fertilization and artificial egg activation. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Egg activation at fertilization in mouse is caused by a series of cytosolic Ca2+ oscillations. Sperm-induced Ca2+ oscillations stimulate mitochondrial oxidative phosphorylation and an ATP increase in the mouse egg. I have investigated the dynamics of intracellular Ca2+ and ATP in mouse eggs caused by sperm and other stimuli. The increase in ATP in fertilizing mouse eggs generally occurs in two phases. The initial ATP increase starts at the same time as the first Ca2+ increase (within 10 sec). The secondary phase of ATP increase is seen ∼1 h after the start of the initial increase, and these changes in ATP still occur when Ca2+ oscillations are inhibited with low concentrations of BAPTA which is a specific Ca2+ chelator. Other stimuli that cause Ca2+ oscillations, such as PLCz1 or thimerosal, failed to cause any secondary phase of ATP increase. Changes in NADH, FAD and mitochondrial membrane potential in response to Ca2+ oscillation were also investigated, but no evidence for a secondary change in activity was seen for these mitochondrial parameters. The data suggest that the secondary increase in ATP at fertilization is Ca2+ independent and may be caused by sperm-specific factors. Some studies were carried out to investigate the potential mechanism by sperm may stimulate the secondary increase in ATP. I have also investigated ways of stimulating ATP production in mitochondria in mouse eggs using numerous intermediates membrane permeable metabolites. Only dimethyl succinate caused a clear increase in luciferase signals suggesting that it can stimulate mitochondria activity in mouse eggs. Furthermore, I have investigated the possible existence of ATP gradients in mouse eggs by measuring the distribution of ATP stimulated luciferase luminescence in eggs that had been stratified by centrifugation. I found no evidence of ATP gradient in mouse eggs, despite the fact that they contained all their mitochondria at one end of an elongated-shaped cell. Finally, I studied the ability of Ca2+ ionophores and other chemicals to cause multiple Ca2+ increases and activation of mouse or sheep eggs. Multiple treatments of eggs with Ca2+ ionophores could only generate one large Ca2+ transient. In contrast, I found that some other specific chemicals could cause multiple Ca2+ transients in mouse eggs in response to sequential additions. These agents cause mouse egg activation and trigger early development more effectively than Ca2+ ionophores. The studies suggest some novel protocols to induce egg activation in mammals.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	9 May 2025
Last Modified:	12 May 2025 13:57
URI:	https://orca.cardiff.ac.uk/id/eprint/178176

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