Alteration of mRNA abundance, oxidation products and antioxidant enzyme activities during oocyte ageing in common carp Cyprinus carpio.

Azin Mohagheghi Samarin,Tone-Kari Knutsdatter Østbye,Viktoriia Burkina,Miroslav Blecha,Sabine Sampels,Azadeh Mohagheghi Samarin,David Gela,Tomas Policar,Bente Ruyter

doi:10.1371/journal.pone.0212694

Abstract

Oocyte ageing is the most important factor affecting egg quality of several fish species after ovulation. Oxidative stress has been proposed as the initiator of the oocyte ageing process in other vertebrates. To identify the role of oxidative stress and apoptosis on the progress of oocyte ageing in the common carp Cyprinus carpio, changes in the relative mRNA abundance of selected transcripts were examined. The possible alteration in the oxidation status of the oocytes during ageing was also studied. In addition, the activity of antioxidant enzymes during oocyte ageing was evaluated. Oocytes from 6 females were incubated in vivo for 14 hours post-ovulation (HPO) and in vitro for 10 hours post-stripping (HPS) at 20°C before fertilization. Hatching rates were over 65% up to 4–6 HPO, finally dropping to 1.3% at 12–14 HPO.Hatching rates were over 65% up to 4–6 HPO, finally dropping to 1.3% at 12–14 HPO. Hatching rates were more than 70% for the eggs stored in vitro up to 6 HPS and then decreased to 21.3% at 10 HPS. The results demonstrated no significant changes in the relative mRNA levels of oxidative stress-related genes or genes involved in the cell cycle during the progress of oocyte ageing in common carp. Additionally, the amount of TBARS and carbonyls did not change as time elapsed following ovulation. The apoptosis-related genes however, were significantly altered following the prolonged time interval between ovulation and fertilization. The lack of response of both activities of antioxidant enzymes and oxidation products during oocyte ageing strengthens the conclusion that oxidative stress is unlikely to be a main factor determining the progress of oocyte ageing in common carp. However, an increase in the mRNA abundance of apoptosis-related genes demonstrates that apoptotic pathway might be involved in the progress of oocyte ageing.

Highlights

Fertilization success, embryo quality and later life of the offspring are highly dependent on the integrity of the oocyte, which contains important information for orchestrating embryogenesis [1, 2] and for remodelling parental genomes [3, 4]
The present study examines some cellular and molecular changes associated with oocyte ageing in the common carp Cyprinus carpio, focusing on the possible role of oxidative stress on the progress of the time-dependent oocyte over-ripening process
Most authors believe that the onset of ageing in oocytes is associated with an increase in reactive oxygen species (ROS), leading to an increase in oxidative stress [23,24,25, 45]

Summary

Introduction

Fertilization success, embryo quality and later life of the offspring are highly dependent on the integrity of the oocyte, which contains important information for orchestrating embryogenesis [1, 2] and for remodelling parental genomes [3, 4]. The eggs remain in the ovarian or body cavity until the occurrence of spawning, which is stimulated by environmental factors, or until the eggs are collected by artificial techniques. Major morphological, physiological, biochemical, histological, cellular and molecular changes occur inside the eggs [9]. These changes deteriorate the quality of ovulated eggs and lead to a limited fertilization rate [10, 11], increased larval malformation [12,13,14] and increased ploidy anomalies [15, 16]. The successful egg storage time time period during which eggs remain viable after ovulation and stripping varies from a few minutes to a few weeks depending on the fish species and storage temperature [9]

Methods

Results

Conclusion