Melatonin improves the quality of frozen bull semen and influences gene expression related to embryo genome activation

The efficiency of animal artificial breeding in vitro is still low. Oxidative damage is an important obstacle for in vitro artificial breeding of animals. Melatonin can reduce the degree of oxidative damage to both gametes and embryos caused by the external environment. However, there is still some controversy concerning the effect of melatonin on frozen semen, especially in the processes of freezing semen, IVM, IVF and IVC. Here, the effects of melatonin on the whole processes of sperm cryopreservation, oocyte maturation, and embryonic development were studied. The results demonstrated that melatonin at 10(-3) M concentration significantly improved progressive sperm viability, plasma membrane integrity, mitochondrial membrane integrity, and acrosome integrity; however, there were also individual dif-ferences between bulls, depending on the age of different individuals. The 10(-3) M melatonin treatment reduced the reactive oxygen species (ROS) level by nearly 50% in sperm during IVF. Meanwhile, during IVM, the addition of 10(-7) M melatonin significantly increased the maturation rate of oocytes and reduced the ROS levels by 58.8%. In addition, 10(-7) M melatonin improved the total cell numbers of the IVF blastocysts. Notably, treatment of IVF embryos with melatonin significantly reduced the levels of ROS and influenced the expression levels of key regulatory genes associated with embryo genome activation. This study is of significance for understanding the function of melatonin in animal artificial breeding. (c) 2021 Elsevier Inc. All rights reserved.