Abstract
Decreasing egg quality following oocyte ageing is a major restricting factor for the breeding programs. The mechanisms behind this process has not yet been clarified. To examine the possible involvement of oxidative stress in the oocyte ageing process, the relative mRNA abundance of specific transcripts were determined in oocytes collected from 6 females and incubated in vitro for 18 hours post stripping at 20 °C in goldfish Carassius auratus. During the 18 hour-post-stripping ageing of the oocytes, relative mRNA levels of candidate transcripts involved in oxidative injury, mitochondrial function and stress response, cell cycles, apoptosis, reproduction and germ line speciation and developmental competence were measured by real-time PCR. None of the relative mRNA abundance of the examined genes were significantly altered through oocyte ageing. In addition, the amount of thiobarbituric acid reactive substances (TBARS), an indicator of lipid peroxidation, did not change over time following stripping. The activity of the antioxidant enzymes also remained constant during oocyte ageing. The results of the current study indicated that oxidative stress unlikely plays a role as an initiator or promotor in the progress of oocyte ageing in goldfish.
Highlights
The meiosis in female germ cell is accompanied by changes in nucleus and cytoplasm, preparing oocyte to be fertilized and subsequently develop into an embryo[1]
The transcript abundance of genes involved in oxidative damage, stress response and mitochondrial function, genes with roles in fertilization, embryo development, cell cycling as well as the gene related to the apoptosis were investigated during oocyte ageing
Previous studies in other vertebrates have suggested that Reactive Oxygen Species (ROS) and subsequently oxidative stress in oocytes increase during post-ovulatory ageing [e.g.20–23]
Summary
The meiosis in female germ cell is accompanied by changes in nucleus and cytoplasm, preparing oocyte to be fertilized and subsequently develop into an embryo[1]. The ageing process of the oocytes is the most important factor that could affect egg quality. This has already been shown in several fish species. It has been suggested that increased Reactive Oxygen Species (ROS) and oxidative stress might be the initiator of oocyte ageing deteriorations [e.g.8,20–22,] This leads to lowered ATP production and irregular Ca2+ oscillation changes. The transcript abundance of genes involved in oxidative damage, stress response and mitochondrial function (hsp[70], cox[1], sodMn, calmodulin), genes with roles in fertilization (vasa), embryo development (igf2), cell cycling (cyclinA, cyclinA2, cyclinB and jnk) as well as the gene related to the apoptosis (ctpb) were investigated during oocyte ageing
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