Mitochondrial characteristics in oocytes of the domestic cat (Felis catus) after in vitro maturation and vitrification.

CONTENTS: The objective of this study was to evaluate mitochondria in immature and in vitro-matured domestic cat oocytes and to assess for the first time the effect of vitrification on mitochondrial traits. Mitochondrial distribution and aggregation were assessed using confocal microscopy after staining with the fluorescent dye-MitoTracker® Red CMXRos. Only cells at the germinal vesicle and the metaphase II stages of nuclear development, representing immature and mature oocytes, respectively, were included in our study. Our study shows that 80% of immature and 100% of mature oocytes exhibit a peripheral pattern of mitochondria distribution, indicating that, in contrast to the situation in other species, the mitochondria of cat oocytes are not dispersed throughout the cell after in vitro maturation but instead maintain a strong affinity for the oocyte periphery near the membrane. However, a loss of aggregation was observed during in vitro maturation-78% of immature oocytes showed homogeneous granulation versus only 18% of mature oocytes (p < .001). The increased intensity of MitoTracker® Red CMXRos staining after in vitro maturation (p < .05) may be tentatively attributed to an increase in mitochondrial activity but could likewise reflect a concomitant appearance of sulphhydryl groups in cytoplasm (known to be targeted by the dye). Mitochondrial distribution did not change upon vitrification; however, dye intensity decreased (p < .05) and mitochondrial aggregation was intensified in both immature and mature vitrified cat oocytes.