Mitochondria and mitochondrial DNA in porcine oocytes and cumulus cells — A search for developmental competence marker

• Growth environment (follicular fluid and cumulus cells) significantly influence the developmental competence of oocytes
• The prepubertal and cyclic gilts differ significantly in terms of oocyte and embryo developmental competence
• MtDNA copy number in cumulus cells correlate with mtDNA copy number in individual oocytes before in vitro maturation
• Puberty does not influence the mtDNA copy number and mitochondria distribution in oocytes
• Every fourth oocyte is useless for IVF due to mtDNA copy number which is too low to support early embryonic development

The development of mammalian oocytes is dependent on bidirectional signaling with the surrounding cumulus cells. Among the numerous factors that contribute to oocyte developmental competence, the mitochondria and the mitochondrial DNA play pivotal roles. Although these highly abundant organelles have been well-studied in oocytes, their roles, abundance and metabolism remain elusive in cumulus cells. Therefore, the aim of our study was to analyze the correlation between the mtDNA copy number in cumulus cells and oocytes, as well as the mitochondrial distribution patterns in oocytes, using two groups of animals that differ in terms of the developmental competence of their oocytes. We determined a positive correlation between the mtDNA copy number in the cumulus cells and mtDNA copy number in oocytes of prepubertal pigs and negative correlation in cyclic gilts. These opposing correlations may reflect the differences in the developmental competence of the prepubertal and cyclic oocytes. We also hypothesize that observed differences may reflect different metabolism and energy requirements of the cumulus–oocyte complexes from prepubertal and cyclic gilts. The mitochondrial distribution patterns in the prepubertal and cyclic gilts were not different.