Mitochondrial Patterns in Bovine Oocytes with Different Meiotic Competence Related to Their in vitro Maturation

Abstract

This study was designed to specify chromatin and mitochondrial patterns in bovine oocytes with different meiotic competence in relation to maturation progress, resumption of meiosis, MII onset and completion of maturation. Oocytes with greater or lesser meiotic competence, recovered separately from medium (MF) and small follicles (SF), were categorized according to morphology. Four oocyte categories, healthy and light-atretic MF and healthy and light-atretic SF oocytes were matured and collected at 0, 3, 7, 16 and 24 h of maturation. Specific differences in terms of chromatin and mitochondrial patterns were found among the maturing oocyte categories. Resumption of meiosis was accelerated in light-atretic oocytes, as compared with healthy oocytes, regardless of their meiotic competence. More competent oocytes activated mitochondria twice during maturation, before resumption of meiosis and before completion of maturation, while less competent oocytes did it only once, before completion of maturation. Changes in mitochondrial activity differed in light-atretic compared with healthy in both more and less competent oocytes. Healthy meiotically more competent oocytes formed clusters and produced ATP for the whole time of maturation until its completion, while light-atretic more competent oocytes and healthy less competent oocytes reduced these activities earlier, at MII onset. Contrary to these oocyte categories, light-atretic less competent oocytes increased cluster formation significantly before resumption of meiosis. It can be concluded that bovine oocytes with different meiotic competence and health differed in the kinetics of mitochondrial patterns during maturation.

<b>The relationship between antral follicle count in a bovine ovary and developmental competence of </b><i><b>in vitro</b></i><b>-grown oocytes derived from early antral follicle</b><b>s </b>

“…Huang et al (19,20) reported that in vitro-grown oocytes acquired high mitochondrial activity after 10-h prematurational culture, and showed higher maturation and development competences compared to oocytes without prematurational culture. Jeseta et al (24) reported that the kinetics of mitochondrial activity and adenosine triphosphate (ATP) production during maturational culture were influenced by the atretic grade of granulosa cells. This indicates the importance of the correlation between oocyte and granulosa cells.…”

Lipid Metabolism in Bovine Oocytes and Early Embryos under In Vivo, In Vitro, and Stress Conditions

“…However, after maturation, oocytes exhibit a large percentage of mitochondria with high activity [24]. Additionally, mitochondrial activity is especially high in oocytes with better morphological quality and competence, wherein changes in the distribution pattern (in particular, the aggregation pattern of mitochondria in the cytoplasm), and high ATP production are observed [27][28][29]. The association between increased mitochondrial activity and changes in their distribution can be described not only in cattle but also in other species (e.g., pig: [30]; horse: [31]).…”

C-X-C motif chemokine ligand 12 improves the developmental potential of bovine oocytes by activating SH2 domain-containing tyrosine phosphatase 2 during maturation

“…The availability of functional mitochondria is important for oocyte developmental competence [53], while mitochondrial clustering is conducive to ATP production. A high incidence of oocytes with mitochondrial granulations at the GV stage or mitochondrial clusters at MII stage has been associated with strong meiotic competence [37, 54]. When CXCR4 or SHP2 inhibitors were applied, many oocytes showed abnormal mitochondrial distribution and decreased mtDNA copy numbers (Figure 6A–C).…”