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Tissue transplantation and in vitro ovarian follicle culture have been investigated as alternative techniques to restore fertility in young women who are facing fertility-threatening diseases or treatments following ovarian tissue cryopreservation. Although transplants of fresh or frozen ovarian tissue have successfully yielded healthy live births in different species including humans, the risks of reintroducing cancer cells back into the patient, post treatment, have limited its clinical purpose. The in vitro ovarian follicle culture minimizes these risks and provides a way to harvest more mature oocytes, however its clinical translation has yet to be determined. Not only is it possible for tissue cryopreservation to safeguard fertility in cancer patients, this technique also allows the maintenance of germplasm banks for animals of high commercial value or for those animals that are at risk of extinction. Given the importance of managing female genetic material, this paper reviews the progress of the methods used to preserve and restore female fertility in different species to demonstrate the results obtained in the past 50 years of research, the current achievements and the future directions on this field. [ABSTRACT FROM PUBLISHER]

Background: Cryopreservation is a biotech successfully employed in female gametes and embryos. This technique is of great importance for propagation of genetic material from animals with high-value livestock as well as to preserve the fertility of women undergoing cancer treatments. However, low temperatures can result in damage to different cellular compartments and organelles. This damage culminates in reduced viability, since they affect cell metabolism. Review: Cryopreservation consists of maintenance of biological material at low temperatures, in which chemical reactions are ceased, however, allowing the cells to preserve their viability. However, the decrease of temperature and subsequent warming may result in cellular damage. These damages occur in the cell membrane, cytoplasmic organelles and the cell nucleus. It is believed that the first cell structure undergoing cryoinjury is the plasma membrane, responsible for maintaining homeostasis within the cell, and the loss of plasma membrane during the reduction temperature reported the main damage. The membrane damage due to cryopreservation appears to correlate with the reduction of thermal energy at low temperatures, thus limiting the movement of molecules through the phospholipids of lipid bilayer. Cryopreservation also alters the morphology, structure and cellular distribution of lipid droplets, reducing the survival of oocytes and embryos. The physical state changes, besides changing physicochemical properties of intracellular lipid may also result in damage to lipids associated with the cellular cytoskeleton. The interaction between cell lipid phase and components of cytoskeleton is complex and hardening of these lipids can cause deformation and disruption of cytoskeleton with consequent negative effect on cell survival and development. The disruption of cytoskeleton can also be intrinsic to change in dehydration and cellular form that follow the cryopreservation process. Among the cellular organelles, mitochondria are sensitive to cryopreservation procedures, since the formation of intracellular ice crystals considered one of the most relevant cryoinjury, leading to damage to the mitochondrial cristae and matrix. Another important organelle undergoes damage as result of cryopreservation is the endoplasmic reticulum, which change in morphology has been described after vitrification of embryos. It is also known that cryopreservation may result in fragmentation of DNA even in the absence of deformation of the cellular morphology, and that these changes can lead to delay in the development or cell death. In addition to the direct damage to double-stranded DNA, cryopreservation may trigger chromosomal abnormalities, these the aneuploidy is the most frequent and seems to compromise the developmental competence of oocytes in addition to being indicated as the main factor for the low achieve of live births. Conclusion: Cryopreservation is an important alternative for the preservation of gametes and embryos, however, the cells are subjected to unfavorable conditions that can compromise cell recovery after thawing/warming. The main cause of reduction in survival oocytes and embryos after cryopreservation appear to be related to damage in different cellular compartments and structures, which are essential for maintaining cell metabolism. Thus, it is observed the need to achieve cryopreservation protocols capable of maintaining the integrity of different cellular components. [ABSTRACT FROM AUTHOR]

Background: Important advances have been made recently that clarify our understanding of the structural basis, signaling and regulation, as well as the biological role of activin in ovaries. During folliculogenesis various growth factors are produced locally in the mammalian ovary. Among these factors, activin has been a focal point in research as it has emerged as a crucial substance capable of inducing follicular development. The important actions indicate that activin has many relevant homeostatic functions in the reproduction of several species. Therefore, this review discusses the ligand protein structure, activin receptors, mechanisms of action and regulation, as well as the importance of activin on in vitro culture of preantral follicles. Review: Activin belongs to the transforming growth factor β (TGF - β) super family. It is a homodimer or heterodimer of two similar but distinct subunits (βA and βB). The dimerisation of activin subunits gives rise to three forms of activin, which are classified as, activin A (βA - βA), activin B (βB - βB) and activin AB (βA - βB). The biological activity of activin occurs through its connection with two types of cell surface receptors designated type I and type II. These receptors are represented by two isoforms, activin receptor types IA (ActR - IA), IB (ActR - IB), IIA (ActR - IIA) and IIB (ActR - IIB). Activin receptors are transmembrane proteins, composed of a ligand-binding extracellular domain, a transmembrane domain and a cytoplasmic domain with serine/threonine kinase activity. The transient activation of the receptor induces phosphorylation of protein mediators called Smads. Activation of Smad 2/3 by phosphorylation causes trimerization and hetero-oligomerization with the common Smad, Smad 4. This complex translocates to the nucleus to activating and regulating transcription of target genes. Members of another class of Smads act as negative regulators of the signal transduction pathway. Inhibitory Smad 7 can bind to type I receptors, preventing receptor--Smad 2/3 association, or by competitively binding of Smad 4, which blocks Smad intracellular translocation. In addition, within the extracellular environment, binding proteins such as follistatin and inhibin can modulate the biological activity of activin. In the ovaries of mammals specifically, activin participates in several cellular events, including cellular proliferation, differentiation, and survival, as well as assisting steroidal hormones during follicular development. Activin has been localized in the oocytes and granulosa cells of rodent, porcine, caprine and bovine follicles. Activin is also within the granulosa cells of human follicles and in the thecal layers of porcine and human. In addition, activin stimulates follicle growth in-vitro, is used in pre-antral ovine and caprine follicles and enhances growth and survival of human pre-antral follicles in vitro. Conclusion: Activin is controlled by competitive substances and a dynamic interaction between the various regulatory proteins responsible for coordinating several signaling pathways. The balance between the actions of these proteins is critical for regulation of gene expression in different structures, including pre-antral follicles. However, the nature of physiological effects of activin in the ovary is still equivocal and awaits clarification. [ABSTRACT FROM AUTHOR]