Dalton, C.M.; (2011) Mitochondrial dynamics during mouse oocyte maturation. Doctoral thesis , UCL (University College London).

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Abstract

Mitochondria provide the primary source of ATP for the oocyte and pre-implantation embryo and undergo a number of redistributions during oocyte maturation which may be related to developmental competence. The experiments presented in this thesis aim to examine the changes in distribution and function of mitochondria during the transition from the germinal vesicle stage to the mature metaphase II arrested egg. Mitochondrial distribution was monitored throughout oocyte maturation and accumulation of mitochondria around the first meiotic spindle was observed. This was dependent on the activities of microtubules and their associated motor proteins dynein and kinesin. Migration of the spindle to the oocyte cortex was accompanied by mitochondria but at polar body extrusion a dramatic reorganisation of mitochondria away from the cortical domain occurred, suggesting that a mechanism exists for retention of these important organelles in the oocyte during this asymmetric cell division. The role of the mitochondrial adapter proteins Trak and Miro in establishing redistribution of mitochondria was also addressed. Finally, a novel recombinant FRET probe for measuring ATP was validated for use in oocytes. Use of this probe revealed alterations to both ATP levels and ATP consumption at different stages of oocyte maturation. Furthermore, whilst the first meiotic spindle was found to be dependent on mitochondrial activity to retain its structure and function, attempts to identify subcellular heterogeneity in ATP supply and demand related to the distribution of mitochondria around the spindle did not reveal any differences. However, the presence of cumulus cells surrounding the oocyte as part of a cumulus-oocyte complex was found to influence ATP levels in the oocyte; oocytes matured as part of a cumulus-oocyte complex had higher ATP levels than those observed in oocytes which had been denuded of cumulus cells. This was found to be dependent on the presence of gap junctional communication between the somatic and germ cell compartments, since inhibition of gap junctions abolished the higher ATP levels observed in cumulus enclosed oocytes.

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