Differential effects of activin-A and FSH on growth, viability and messenger RNA expression in cultured bovine preantral follicles

The mechanisms that control the preantral to early antral follicle transition and the strategies to have efficient culture systems to promote their growth in vitro

Preantral to early antral follicles transition is a complex process regulated by endocrine and paracrine factors, as well as by a precise interaction among oocyte, granulosa cells and theca cells. Understanding the mechanisms that regulate this step of folliculogenesis is important to improve in vitro culture systems, and opens new perspectives to use oocytes from preantral follicles for assisted reproductive technologies. Therefore, this review aims to discuss the endocrine and paracrine mechanisms that control granulosa cell proliferation and differentiation, formation of the antral cavity, estradiol production, atresia, and follicular fluid production during the transition from preantral to early antral follicles. The strategies that promote in vitro growth of preantral follicles are also discussed.

In vitro long-term culture of isolated ovine preantral follicles: Influence of ethanol on steroid production, oocyte meiotic resumption, and metabolomic profile

Ethanol is used routinely to dilute cell culture media supplements with little or no water solubility. This study evaluates the effect of low concentration of ethanol on the follicular development, oocyte maturation, hormone production, gene expression, and metabolomics profile of spent culture medium after long-term culture of isolated ovine preantral follicles. For this, follicles were cultured for 18 days in α-Minimum Essential Medium⁺ alone (control treatment) or supplemented with 100 ng/mL recombinant bovine FSH (rbFSH treatment) or with 0.2%-v/v ethanol (ethanol treatment). Ethanol treatment increased the percentage of degenerated follicles and oocytes significantly, however, it showed the highest estradiol secretion. Also, the rate of meiosis resumption was higher in ethanol treatment than Control treatment. Ethanol treatment decreased the mRNA levels of B-cell lymphoma 2 (BCL2), BCL2 associated X, Aquaporin 3, Connexin 43, Inhibin Subunit Beta A, kit ligand, Heat Shock Protein (HSP A1A) significantly when compared to the Control treatment. However, mRNA levels of cytochrome P450 family 19, and FSH receptors were significantly higher in ethanol treatment than in the Control treatment. The levels of some metabolites, which are likely amino acids, lipids, an analog of Cyclic guanosine monophosphate, and a derivative of phosphoinositol phosphate metabolism, had higher relative concentrations in ethanol and rbFSH treatments than the Control treatment. In conclusion, ethanol addition augmented the follicular and oocyte degeneration rates but increased the estradiol production and the meiotic resumption. Furthermore, the follicular metabolomic profile was similar between ethanol and rbFSH treatments being both treatments; however, different from the Control treatment.

Activin promotes growth and antral cavity expansion in the dog ovarian follicle

Understanding regulators of folliculogenesis remains limited in the domestic dog (Canis familiaris), which challenges our ability to develop in vitro follicle culture systems for canid genome rescue efforts. Here, we investigated the influence of activin on dog follicle development and survival, oocyte quality, and FSH receptor expression in culture. Preantral (150 - ≤230 μm diameter), early antral (231 - ≤330 μm), and antral (>330-550 μm) stage follicles were encapsulated in a fibrin-alginate hydrogel with 0, 100, or 200 ng/ml rhActivin plus 0, 0.1, 1, or 10 μg/ml FSH for 12 or 21 d of in vitro culture. All follicle groups increased in diameter (P < 0.05) with activin acting synergistically with FSH to improve (P < 0.05) growth and antral cavity expansion (to >630 μm) in early antral and antral cohorts. This complementary effect was not linked to changes in FSHR mRNA expression (P > 0.05). Although not influencing (P > 0.05) follicle survival or transzonal projection (TZP) density in shorter term 12 d culture, activin in the presence of 1 ng/ml FSH maintained TZP density from the 12-21 d interval. Activin also increased oocyte diameter and improved nuclear integrity compared to un-supplemented controls. These results indicate that activin acts synergistically with FSH to promote growth and antral cavity expansion of the dog follicle in vitro, information useful to formulating an effective culture microenvironment for this species.

The Growth of Preantral Follicles and the Impact of Different Supplementations and Circumstances: A Review Study with Focus on Bovine and Human Preantral Follicles

One of the most important concerns cancer survivors face is fertility. Current treatment modalities often result in damage to the reproductive system. Different options have been proposed to preserve the fertility of affected women, and many attempts have been made to improve their chance of childbearing after therapy. Cryopreservation of ovarian tissue and follicles before the onset of cancer treatment and then either transplantation of ovarian tissue or culture of ovarian tissue and individual follicles in vitro is a commonly cited approach. Extensive research is being done to design an optimal condition for the culture of ovarian follicles. Improving follicle culture systems by understanding their actual growth needs might be a crucial step toward fertility preservation in cancer patients. This review article will try to provide a summary of the role of different factors and conditions on growth of human and bovine preantral follicles in vitro.

Ovarian follicle development in vitro and oocyte competence: advances and challenges for farm animals

During the last 2 decades, research on in vitro preantral follicle growth and oocyte maturation has delivered fascinating advances concerning the knowledge of processes regulating follicle growth and the developmental competence of oocytes. These advances include (1) information about the role of several hormones and growth factors on in vitro activation of primordial follicles; (2) increased understanding of the intracellular pathway involved in the initiation of primordial follicle growth; (3) the growth of primary and secondary follicles up to antral stages; and (4) production of embryos from oocytes from in vitro grown preantral follicles. This review article describes these advances, especially in regard farm animals, and discusses the reasons that limit embryo production from oocytes derived from preantral follicles cultured in vitro.