Intrafollicular barriers and cellular interactions during ovarian follicle development

Abstract

Folliclesare composed of different interdependent cell types including oocytes, cumulus, granulosa, and theca cells. Follicular cells and oocytes exchange signaling molecules from the beginning of the development of the primordial follicles until the moment of ovulation. The follicular structure transforms during folliculogenesis; barriers form between the germ and the somatic follicular cells, and between the somatic follicular cells. As such, communication systems need to adapt to maintain the exchange of signaling molecules. Two critical barriers are established at different stages of development: the zona pellucida, separating the oocyte and the cumulus cells limiting the communication through specific connections, and the antrum, separating subpopulations of follicular cells. In both situations, communication is maintained either by the development of specialized connections as transzonal projections or by paracrine signaling and trafficking of extracellular vesicles through the follicular fluid. The bidirectional communication between the oocytes and the follicle cells is vital for driving folliculogenesis and oogenesis. These communication systems are associated with essential functions related to follicular development, oocyte competence, and embryonic quality. Here, we discuss the formation of the zona pellucida and antrum during folliculogenesis, and their importance in follicle and oocyte development. Moreover, this review discusses the current knowledge on the cellular mechanisms such as the movement of molecules via transzonal projections, and the exchange of extracellular vesicles by follicular cells to overcome these barriers to support female gamete development. Finally, we highlight the undiscovered aspects related to intrafollicular communication among the germ and somatic cells, and between the somatic follicular cells and give our perspective on manipulating the above-mentioned cellular communication to improve reproductive technologies.

Ovarian Dysfunction Induced by Chronic Whole‐Body PM2.5 Exposure

“…[ 55–56 ] The fate of follicles is determined by the microenvironment of follicles and various signals inside and outside cells. [ 57,58 ] Moderate primordial follicle activation and follicular atresia are essential for maintaining normal ovarian function. Here, our data showed that PM2.5‐induced oxidative stress and inflammation triggered apoptosis in ovaries.…”

Morphology of male and female reproductive tract of the ocelot (Leopardus pardalis)

“…The oviducts are small with a pink coloration, conformation and anatomical positioning similar to the findings of Dyce et al (2010) in domestic canids and felines and Machado et al (2017) in crab-eating fox. The importance of this organ and continuous studies must be highlighted (Andrade et al, 2019).…”

Extracellular Vesicles as Mediators of Environmental and Metabolic Stress Coping Mechanisms During Mammalian Follicular Development

“…The follicular microenvironment has two physical barriers that separate the oocyte from the follicular cells, the follicular fluid-filled antrum and the zona pellucida (ZP). Nevertheless, the constant flow of information between the oocyte and the follicular cells is maintained through the transzonal projection (TZP), irrespective of the physical barriers (18). The cumulus cells, which are located adjacent to the oocyte are the primary origin of the TZP.…”