Abstract
Most of the mammalian follicles undergo a degenerative process called “follicle atresia”. Apoptosis of granulosa cells is the main characteristic of follicle atresia. Follicle stimulating hormone (FSH) and the transforming growth factor β (TGF-β) superfamily have important regulatory functions in this process. FSH activates protein kinase A and cooperating with insulin receptor substrates, it promotes the PI3K/Akt pathway which weakens apoptosis. Both Smad or non-Smad signaling of the transforming growth factor β superfamily seem to be related to follicle atresia, and the effect of several important family members on follicle atresia is concluded in this article. FSH and TGF-β are likely to mutually influence each other and what we have already known about the possible underlying molecular mechanism is also discussed below.
Highlights
Folliculogenesis is a process describing the fate of oocytes and their surrounding somatic cells
Granulosa cells become cuboidal when primordial follicles mature into primary follicles and they turn into multilayers when they enter the stage of secondary follicles [1]
We mainly focus on signaling mechanisms of Follicle stimulating hormone (FSH) and depict a network of those two pathways which enables the role of FSH in follicle atresia
Summary
Folliculogenesis is a process describing the fate of oocytes and their surrounding somatic cells. Apoptosis first occurs at oocytes in preantral follicles and at granulosa cells of follicles in later stages of development [2]. In porcine ovarian follicles undergoing atresia, expression level of the anti-apoptotic bcl-2 family protein increases together with that of pro-apoptotic genes, possibly to prevent cell death [11]. The ratio of them gets out of balance, with relatively higher pro-apoptotic gene expression in atretic follicles at different stages [12] This indicates that in ovaries, intercellular survival factors can play an essential role in follicle maintenance since intrinsic apoptotic pathways are often related to the lack of survival factors. Interaction between oocytes and granulosa cells is critical to growth and differentiation of follicles This kind of communication is carried out by intra-ovarian factors and is mutually beneficial [13]. It is the first review to discuss the crosstalk between cAMP/PKA and PI3K/Akt pathways stimulated by follicle stimulating hormone in the ovarian environment and some aspects of the possible molecular mechanism how follicle stimulating hormone and transforming growth factor beta superfamily interact with each other are suggested here
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