Abstract
Simple SummaryMelatonin improves the quality and in vitro maturation (IVM) of oocytes under heat stress. Melatonin treatment counteracts the adverse effects induced by heat stress (HS), such as the poor survival rate and maturation rate, distribution of α-tubulin and F-actin, expression of NRF2 and GDF9 mRNA. However, HS and melatonin have similar effects on increasing expression of HSP70 and NRF2 mRNA. Furthermore, HS inhibits expression of GDF9 mRNA.Melatonin enhances the quality and in vitro maturation (IVM) of oocytes under heat stress (HS), but the mechanism of melatonin in reducing HS injury on oocytes is not fully understood. In this study, porcine cumulus-oocyte complexes (COCs) were randomly divided into three groups. The COCs of the control group were cultured at 38.5 °C for 42 h, and the COCs of the HS group were cultured at 41.5 °C for 4 h, and then transferred into 38.5 °C for 38 h. The COCs of the HS + melatonin group were cultured with 10−9 M melatonin under the same conditions as the HS group. The survival rate, maturation rate, distribution of α-tubulin and F-actin of the oocytes were assessed. In addition, the expression profiles for genes related to the oocyte maturation, including heat shock protein 70 (HSP70), nuclear factor erythroid 2-related factor 2 (NRF2), cyclin-dependent kinase 1 (CDK1), growth differentiation factor 9 (GDF9) were analyzed by real-time quantitative PCR. The results showed that HS decreased the survival rate and maturation rate, distribution of α-tubulin and F-actin, but melatonin treatment could partly counteract these adverse effects. In addition, HS increased expression of HSP70 and NRF2 mRNA, and melatonin treatment had a similar effect on HSP70 expression, but had a contrary effect on NRF2 expression. Furthermore, HS inhibited expression of CDK1 and GDF9 mRNA, but melatonin treatment could weaken the effect on GDF9 expression induced by HS. In summary, melatonin treatment could attenuate the unfavorable effects induced by HS to enhance developmental competence of porcine oocytes during IVM.
Highlights
The data showed that the oocyte survival rate of the control group was higher than that of the heat stress (HS) group and HS + melatonin (HSMT) group (p < 0.05; Table 2), but there was no significant difference between the HS group and HSMT group (p > 0.05; Table 2)
Our results indicated that HS had adverse effects on the survival rate and maturation rate of the oocytes during in vitro maturation (IVM), but melatonin could counteract the unfavorable effect on the maturation rate of the oocyte
HS had adverse effects on the survival rate and maturation rate, distribution of α-tubulin and filamentous actin (F-actin) of the oocytes, but melatonin treatment could partly counteract these adverse effects during IVM
Summary
The fertility of female rabbits decreases, but a quercetin-supplemented diet reduces ovarian apoptosis, and maintains the oocyte competence during summer HS [3]. In vitro maturation (IVM) is used routinely in the in vitro production of embryos for the research and production of offspring in breeding programs in domestic species [6]. HS induces ceramide generation to cause reactive oxygen species (ROS) production and mitochondrial dysfunction, which reduce the proportion of cumulus-oocyte complexes (COCs) exhibiting fully expanded cumulus cells and the rate of metaphase II in porcine oocytes [7]. HS has significant effects on the nucleus and cytoskeleton of IVM bovine oocytes, which is related to the low pregnancy rates in domestic species during hot seasons [8]
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