Ca2+ and mitochondrial ATP production at fertilization in mouse eggs

Ikie, Cindy 2025. Ca2+ and mitochondrial ATP production at fertilization in mouse eggs. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

At fertilization in mouse eggs, oscillations in the cytosolic Ca2+ concentration, [Ca2+]c, are triggered by fused sperm which release PLCζ1 into the egg cytosol resulting in the activation of development. During these [Ca2+]c oscillations, ATP levels have previously been shown to rise in two distinct phases, with the initial increase occurring simultaneously with the first [Ca2+]c transient, and a second increase starting approximately 1 hour later. I find that the second change in ATP is sperm dependent because it does not occur with other stimulants that trigger repetitive [Ca2+]c oscillations such as PLCζ1, thimerosal or strontium. Furthermore, when repetitive [Ca2+]c oscillations were prevented in eggs at fertilization using the Ca2+ chelator BAPTA, there was still a two-step ATP increase in eggs. In addition, the fertilization of eggs with Plcζ1 KO sperm leads to a two-step change in ATP similar to control fertilized eggs. With Plcζ1 KO sperm, the initial ATP rise occurs about 40 mins before the occurrence of a set of small Ca2+ oscillations, and the second ATP increase occurs during these delayed Ca2+ oscillations. The second change in ATP was not reflected by any clear change in the NAD(P)H transients that occur at fertilization. I also investigated changes in cytosolic Mg2+ in fertilizing eggs using different fluorescent dyes but found that Mg2+ was not an effective indicator of ATP changes at fertilization. Finally, I tested numerous chemicals, previously reported to stimulate mitochondria, to see if they could increase ATP levels in eggs and found most were ineffective. One mitochondrial substrate proved capable of causing a significant ATP increase, and this was not accompanied by any [Ca2+]c oscillations. All these data suggest that at fertilization the sperm introduces a factor into the egg, that is not PLCζ1, and that this second factor stimulates ATP production by an unknown mechanism.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	9 April 2026
Last Modified:	17 Apr 2026 10:00
URI:	https://orca.cardiff.ac.uk/id/eprint/186295

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