Characteristics of Bovine Oocytes with Different Meiotic Competence in Terms of Their Mitochondrial Status and Expression of Nuclear‐Encoded Factors

Abstract

The present study was designed to characterize bovine oocytes with different meiotic competence and atresia levels in terms of their mitochondrial status. Oocyte subpopulations were recovered either from medium (MF) or small (SF) follicles and categorized as healthy, light-atretic and mid-atretic according to oocyte morphology. Mitochondrial activity, morphology and distribution, adenosine triphosphate (ATP) content and expression of mitochondrial transcription factor A (TFAM) and nuclear respiratory factor 1 (NRF1) were assessed before (GV) and after (MII) maturation. The data were related to follicular size regardless of or with regard to oocyte atresia. Regardless of atresia, the MF subpopulation showed a significantly higher mitochondrial activity and frequency of oocytes with granulated mitochondria at GV and clustered mitochondria at MII than the SF subpopulation. With regard to atresia, mitochondrial activity decreased from healthy to mid-atretic oocytes in both MF and SF subpopulations at GV, but in the SF subpopulation at MII, the mitochondrial activity and frequency of oocytes with clustered mitochondria were significantly higher in light-atretic than in healthy oocytes. The light-atretic oocytes also produced more ATP than healthy ones in both SF and MF subpopulations. However, a significantly higher relative abundance of mRNA TFAM was found in SF than MF subpopulations at GV, and this difference remained in mid-atretic oocytes at MII. It can be concluded that meiotic competence and atresia level influence mitochondrial status of immature bovine oocytes. After maturation, healthy oocytes from medium follicles and light-atretic oocytes from small follicles were more developed in terms of mitochondrial status than the other oocytes.

Energy Status Characteristics of Porcine Oocytes During In Vitro Maturation is Influenced by Their Meiotic Competence

“…In our preliminary study, we have described that there are specific differences in the mitochondrial patterns in maturing bovine oocytes with different meiotic competence (Machatkova et al 2012). The present study was designed to compare energy status between meiotically more and less competent porcine oocytes on the basis of mitochondrial-lipid patterns and their changes during maturation because no relevant data in pigs are available.…”

“…Some studies have shown that mitochondrial status is associated with meiotic and developmental competence of rodent, human and cattle oocytes (Bavister and Squirrell ; Van Blerkom ; Machatkova et al. ). The adequate distribution and functions of mitochondria are important for fertilization of mouse oocytes (Nazmara et al.…”

“…Mitochondrial dysfunction including changes in the mitochondrial ultrastructure, an increase in mtDNA copy numbers, decreased ATP levels and tricarboxylic acid (TCA) cycle metabolites correlate with reduced reproductive functions (Bentov and Casper 2013). Some studies have shown that mitochondrial status is associated with meiotic and developmental competence of rodent, human and cattle oocytes (Bavister and Squirrell 2000;Van Blerkom 2011;Machatkova et al 2012). The adequate distribution and functions of mitochondria are important for fertilization of mouse oocytes (Nazmara et al 2014).…”

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

“…To characterize mitochondria more objectively, we studied oocytes obtained from medium and small follicles separately and categorized them as healthy, light‐atretic and mid‐atretic (Machatkova et al. ). The study showed that, independently of meiotic competence, the values of mitochondrial parameters were significantly reduced in mid‐atretic oocytes, as compared with those in light‐atretic and healthy oocytes.…”

“…Although the less competent oocytes showed an increase in mitochondrial activity after maturation, they remained inferior to more competent oocytes in both cluster formation and ATP production (Machatkova et al. ). This study was designed to characterize mitochondrial patterns in bovine oocytes with different meiotic competence in the course of maturation, related to the resumption of meiosis, MII onset and completion of maturation.…”