Centrosome and microtubule functions and dysfunctions in meiosis: implications for age-related infertility and developmental disorders.

The effects of oocyte aging on meiotic spindle dynamics have been well recognised, but the mechanisms underlying the effects are not well understood. In this paper we review the role of centrosomes and the microtubule cytoskeleton in meiotic spindle formation and maintenance, and the impact of oocyte aging on spindle integrity resulting in centrosome and microtubule dysfunctions that are associated with aneuploidy. Loss of spindle integrity includes dispersion of proteins from the centrosome core structure and loss of attachment of microtubules to centrosomes and kinetochores, which will result in abnormal chromosome separation. The inability of centrosomal proteins to accurately associate with the centrosome structure may be the result of destabilisation of the core structure itself or of microtubule destabilisation at the centrosome-facing microtubule areas that are acetylated in fresh oocytes but may not be acetylated in aging oocytes. Microtubule destabilisation prevents accurate motor-driven transport of centrosomal proteins along microtubules to form and maintain a functional centrosome. Other factors to form and maintain the MII spindle include signal transductions that affect microtubule dynamics and stability. Understanding the mechanisms underlying centrosome and microtubule dysfunctions during oocyte aging will allow diagnosis and analysis of oocyte quality and abnormalities as important aspects for targeted treatment of aging oocytes to extend or restore viability and developmental capacity. New therapeutic approaches will allow improvements in reproductive success rates in IVF clinics, as well as improvements in reproductive success rates in farm animals. This review is focused on: (1) centrosome and microtubule dynamics in fresh and aging oocytes; (2) regulation of centrosome and/or microtubule dynamics and function; and (3) possible treatments to extend the oocyte's reproductive capacity and viability span.