The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

The roles of TRAK2 and Miro in microtubule-mediated mitochondria dynamics in mammalian oocytes (#324)

In-Won Lee 1 , Deepak Adhikari 1 , Qing-hua Zhang 1 , Jun Liu 1 , Wai Shan Yuen 1 , John Carroll 1
  1. Development and Stem cells Program and Department of Anatomy and Developmental Biology, Monash Biomedicine Discovery Institute, Monash University, Melbourne

Oocytes have individual mitochondria that undergo a dramatic reorganization as the oocyte progresses through meiosis from the Germinal Vesicle (GV) stage to metaphase II(MII). From a relatively homogeneous cytoplasmic distribution at the GV stage, mitochondria aggregate around the developing meiotic spindle, and then migrate to the cortex with the spindle. After polar body extrusion, as oocytes progress to MII, mitochondria are dramatically and rapidly redistributed throughout the cytoplasm. Mitochondria trafficking in mammalian cells generally occurs along microtubule tracks via motor proteins, dynein, and kinesin. Recent studies in neurons have led to the discovery of mitochondrial adaptor proteins, TRAK1/2 and Miro. We hypothesize that the dynamics of mitochondrial localization during meiosis is controlled by TRAK and Miro. By using mutant variants of these proteins, microinjection, live-cell imaging and quantitative microscopy approaches, we study the role of Trak2 and Miro in mitochondrial trafficking in mouse oocytes. Immunofluorescence reveals TRAK2 and Miro are localized to mitochondria at all stages of oocyte maturation. Over-expression of TRAK2 caused a dramatic increase in mitochondrial aggregation at all stages and very few mitochondria remained distant to the GV or spindle associated cluster of mitochondria. Over-expression of fluorescently tagged TRAK2 deletion mutants lacking the kinesin-binding domain (TRAK2KDM) had a negligible effect on the GV stage but led to an increased accumulation around the spindle, presumably due to reduced kinesin-mediated trafficking to microtubule located +ends in the oocyte cytoplasm. These results suggest that microtubule dynamics in oocytes are regulated in a cell cycle specific manner and involve the adaptor proteins TRAK2 and Miro.