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Kisspeptin is a newly-discovered neurohormone, which is secreted from the hypothalamus. Initially it was thought that kisspeptin takes part in metastasis suppression. However, nowadays it is known that this hormone plays an essential role in the modulation of the hypothalamus-pituitary-gonadal axis. It has been demonstrated that mutation in the gene encoding kisspeptin’s receptor causes hypogonadotrophic hypogonadism and infertility in animals and humans. It is well established that kisspeptin may directly stimulate hypothalamic neurons. In addition, this neurohormone directly affects the pituitary and gonads. In the current review the authors sum up all information about different ways of direct and indirect effects of kisspeptin on reproductive processes and also present a novel insight into the mechanism responsible for the feedback loop of estrogen and androgen in mammals.
The immune-like growth factors (IGF-I, IGF-II and IGFBP) play a significant role in human and animal reproduction. It was found that the receptors for these growth factors are present in the uterine endometrium and in the epithelium of the oviduct, and that the gene expression for these receptors depends on the phases of the estrus cycle. The high concentration of IGF-I and IGF-II receptors in the epithelium of the oviduct and in the uterine glands may suggest that the role of these receptors is to regulate the excretory function of the mucous membrane in order to establish an appropriate environment for embryo development. Moreover, IGF-I and IGF-II act mitogenically intensifying the growth of an early embryo. The impact and growing concentration of these factors in embryogenesis depend on the estrogen action. The action of the immune-like factors is multifunctional and not limited only to stimulation of embryo development. The IGF factors also play an important role in the control of apoptosis.
The process of oocytes maturation in mammals is regulated by the expression of many types of cell-specific genes. Both nuclear and cytoplasmic maturation is based on activation of biochemical and metabolic pathways that lead to reaching the full maturation stage (MII) of oocytes. The most recent data indicates that the proteins belonging to transforming the growth factor beta (TGF-β) superfamily play an important role in the process of oocytes maturation, as well as of reaching full developmental capacity by these cells. Moreover, it has been clearly showed that the proteins belonging to TGF-β such as inhibins (INHA, INHB) and activins regulate both folliculo- and oogenesis by the stimulation and/or inhibition of several biochemical pathways. In this review, the most recent knowledge about the role of proteins belonging to TGF-β superfamily in the regulation of folliculogenesis, oogenesis and oocytes maturation has been presented and discussed.
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