ABSTRACT
The circadian rhythm of mammals is a physiological phenomena that is about 24 hours produced by genetically encoded molecular clocks, making the physiological process of the body coordinated with the changes of the external environment, and it is a manifestation of adaptation to the environment. In mammals, reproductive physiology is regulated by the circadian clock. The expression of circadian clock genes has been observed in each tissue of the hypothalamic-pituitary-ovarian (HPO) axis, and the biological clock at all levels coordinates and synchronizes with each other to maintain normal reproductive behavior. The production, maintenance, and regulation of circadian rhythms depend on a chain of transcription-translation feedback loops (TTLs), which determine the cycle and amplitude of gene expression in each tissue of the HPO axis. The circadian clock of the ovary is regulated by theneuroendocrine regulation of suprachiasmatic nucleus of the hypothalamus, but it is autonomous. Circadian rhythm disruption caused by environmental factors can seriously impair female fertility and lead to a range of related ovarian diseases. In addition, the circadian clock is also closely related to ovarianaging. Based on existing research, this paper focuses on the mechanism of the circadian clock in ovarian follicular development, ovulation and steroid generation, as well as the latest research progress on the relationship between the circadian clock and ovarian aging. In addition, several common ovarian diseases with decreased fertility due to circadian clock disorders are described.
ABSTRACT
Oocytes are the germ cells of female animals, which determine the reproductive ability of female animals. A large amount of lipids are present in oocytes, which are found in lipid droplets mostly in the form of triglycerides. The size, color and distribution pattern of lipid droplets are associated with the developmental ability of oocytes. Triglycerides could be lipolyzed into fatty acids in oocytes. The fatty acid β-oxidation is an important energy source for the development of oocytes and early embryos. However, excessive lipid deposition would increase levels of reactive oxygen species (ROS), resulting in the dysfunction of mitochondria and endoplasmic reticulum, eventually impairing the subsequent oocyte development. By summarizing the positive and negative effects of lipids on oocyte development, this review shows the dual roles of lipids in oocyte development, and discusses the effects of lipids on oocyte development.