Measurement of ATP in Single Oocytes: Impact of Maturation and Cumulus Cells on Levels and Consumption

Caroline M Dalton,Gyorgy Szabadkai,John Carroll

doi:10.1002/jcp.24457

Abstract

Mitochondria provide the primary source of ATP in the oocyte and early embryo and mitochondrial dysfunction and deficit of mitochondria-derived ATP has been linked to suboptimal developmental competence. We have undertaken a study of ATP in the maturing mouse oocyte using a novel recombinant FRET based probe, AT1.03. We show that AT1.03 can be successfully used to monitor cytosolic ATP levels in single live oocytes over extended time periods. We find that ATP levels undergo dynamic changes associated with specific maturational events and that oocytes display altered rates of ATP consumption at different stages of maturation. Cumulus enclosed oocytes have a higher ATP level during maturation than denuded oocytes and this can be abolished by inhibition of gap junctional communication between the oocyte and cumulus cells. Our work uses a new approach to shed light on regulation of ATP levels and ATP consumption during oocyte maturation.

Highlights

Oocyte maturation involves a series of nuclear and cytoplasmic changes which result in the formation of an egg which is competent to undergo fertilization
ATP levels have been successfully monitored in live somatic cells using the recombinant FRET probe AT1.03 (Imamura et al, 2009; Bermejo et al, 2010; Liemburg-Apers et al, 2011; Ando et al, 2012; Khodorov et al, 2012; Kishikawa et al, 2012; Surin et al, 2013) but its use in oocytes has not been described previously
We found that ATP levels rose as meiosis I resumed decreased approximately 1 h after germinal vesicle breakdown (GVBD)

Summary

Introduction

Oocyte maturation involves a series of nuclear and cytoplasmic changes which result in the formation of an egg which is competent to undergo fertilization. Mitochondria are among the most abundant organelles in the oocyte (Sathananthan and Trounson, 2000) and mitochondrial function is thought to be important for successful maturation and early development. The oocyte is surrounded by cumulus cells that are linked to the oocyte by gap junctions (Anderson and Albertini, 1976). These allow bidirectional communication between the oocyte and cumulus cells, which is necessary for the development and activity of both cell types (Eppig, 2001; Sugiura et al, 2005; Gilchrist et al, 2008). In contrast to previous studies investigating ATP levels in oocyte and embryos which have largely used luciferase assays, we have employed a recently developed recombinant FRET probe (Imamura et al, 2009) to investigate ATP levels in the oocyte

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