A synopsis of global frontiers in fertility preservation.

Since 2007, the Oncofertility Consortium Annual Conference has brought together a diverse network of individuals from a wide range of backgrounds and professional levels to disseminate emerging basic and clinical research findings in fertility preservation. This network also developed enduring educational materials to accelerate the pace and quality of field-wide scientific communication. Between 2007 and 2019, the Oncofertility Consortium Annual Conference was held as an in-person event in Chicago, IL. The conference attracted approximately 250 attendees each year representing 20 countries around the world. In 2020, however, the COVID-19 pandemic disrupted this paradigm and precluded an in-person meeting. Nevertheless, there remained an undeniable demand for the oncofertility community to convene. To maintain the momentum of the field, the Oncofertility Consortium hosted a day-long virtual meeting on March 5, 2021, with the theme of "Oncofertility Around the Globe" to highlight the diversity of clinical care and translational research that is ongoing around the world in this discipline. This virtual meeting was hosted using the vFairs ® conference platform and allowed over 700 people to participate, many of whom were first-time conference attendees. The agenda featured concurrent sessions from presenters in six continents which provided attendees a complete overview of the field and furthered our mission to create a global community of oncofertility practice. This paper provides a synopsis of talks delivered at this event and highlights the new advances and frontiers in the fields of oncofertility and fertility preservation around the globe from clinical practice and patient-centered efforts to translational research.

Maternally-derived zinc transporters ZIP6 and ZIP10 drive the mammalian oocyte-to-egg transition.

Rapid cellular zinc influx regulates early mammalian development during the oocyte-to-egg transition through modulation of the meiotic cell cycle. Despite the physiological necessity of this zinc influx, the molecular mechanisms that govern such accumulation are unknown. Here we show that the fully grown mammalian oocyte does not employ a transcriptionally based mechanism of zinc regulation involving metal response element-binding transcription factor-1 (MTF-1), as demonstrated by a lack of MTF-1 responsiveness to environmental zinc manipulation. Instead, the mammalian oocyte controls zinc uptake through two maternally derived and cortically distributed zinc transporters, ZIP6 and ZIP10. Targeted disruption of these transporters using several approaches during meiotic maturation perturbs the intracellular zinc quota and results in a cell cycle arrest at a telophase I-like state. This arrest phenocopies established models of zinc insufficiency during the oocyte-to-egg transition, indicating the essential function of these maternally expressed transporters. Labile zinc localizes to punctate cytoplasmic structures in the human oocyte, and ZIP6 and ZIP10 are enriched in the cortex. Altogether, we demonstrate a mechanism of metal regulation required for female gamete development that may be evolutionarily conserved.

Multiple follicle culture supports primary follicle growth through paracrine-acting signals.

In vitro follicle growth in alginate hydrogels is a unique and versatile method for studying ovarian and follicle biology that may also have implications for fertility preservation. Current culture systems support the development of isolated mouse follicles from the secondary stage onward. However, it has been a challenge to grow smaller follicles in vitro due to the dissociation of the oocyte from companion somatic cells. Recent work has demonstrated that coculturing primary follicles with mouse embryonic fibroblasts or ovarian stromal cells supports follicle survival and growth. In this study, we demonstrate that follicles themselves can exert a beneficial coculture effect. When primary follicles were cultured in groups of five or ten (multiple follicle culture), there was increased growth and survival. The multiple follicle culture approach maintained follicle integrity and resulted in the formation of antral stage follicles containing meiotically competent gametes. The growth and survival of primary follicles were highly number dependent, with the most significant enhancement observed when the largest number of follicles was grown together. Our data suggest that the follicle unit is necessary to produce the secreted factors responsible for the supportive effects of multiple follicle culture, as neither denuded oocytes, oocyte-secreted factors, nor granulosa cells alone were sufficient to support early follicle growth in vitro. Therefore, there may be signaling from both the oocyte and the follicle that enhances growth but requires both components in a feedback mechanism. This work is consistent with current in vivo models for follicle growth and thus advances the movement to recapitulate the ovarian environment in vitro.

Isolated primate primordial follicles require a rigid physical environment to survive and grow in vitro.

BACKGROUND: In vitro follicle growth is a promising fertility preservation strategy in which ovarian follicles are cultured to produce mature and fertilization-competent oocytes. However, in primates, there has been limited success with in vitro follicle growth starting from primordial and primary follicles because adequate isolation methods and culture strategies have not been established. Understanding how to use primordial follicles for fertility preservation has significant implications because these follicles are the most abundant in the ovary, are found in all females and are fairly resistant to cryopreservation and chemotherapeutics. METHODS: In the primate ovary, primordial follicles are concentrated near the collagen-rich ovarian cortex. To obtain these follicles, we separated the ovarian cortex prior to enzymatic digestion and enriched the primordial follicle concentration by using a novel double filtration system. To test the hypothesis that a rigid physical environment, as found in vivo, is optimal for survival, primordial follicles were cultured in different concentrations of alginate for up to 6 days. Follicle survival and morphology were monitored throughout the culture. RESULTS: We found that primate ovarian tissue can be maintained for up to 24 h at 4°C without compromising tissue or follicle health. Hundreds of intact and viable primordial follicles were isolated from each ovary independent of animal age. Follicle survival and morphology were more optimal when follicles were cultured in 2% alginate compared with 0.5% alginate. CONCLUSIONS: By mimicking the rigid ovarian environment through the use of biomaterials, we have established conditions that support primordial follicle culture. These results lay the foundations for studying the basic biology of primordial follicles in a controlled environment and for using primordial follicles for fertility preservation methods.

Animal age, weight and estrus cycle stage impact the quality of in vitro grown follicles.

BACKGROUND: Ovarian tissue cryopreservation is an emerging fertility preservation option, and culturing follicles isolated from this tissue to obtain mature gametes may ultimately be the best solution for patients for whom transplantation is contraindicated. It is unclear, however, how patient-specific variables (including age, weight and menstrual cycle stage) impact follicle growth and quality during three-dimensional culture. METHODS: We used a mouse model to systematically determine how these variables impact in vitro follicle growth. We characterized metabolic and hormonal profiles of mice at specific ages, weights and cycle stages and secondary follicles from these cohorts were isolated and cultured. We then assessed follicle survival, growth and function, as well as meiotic competence and spindle morphology of the resulting oocytes. RESULTS: We found that older mice and mice with increased body weight had higher serum cholesterol, abnormal glucose tolerance and lower levels of circulating Anti-Müllerian hormone compared with younger and leaner controls. Secondary follicles isolated from different cohorts and grown in vitro had indistinguishable growth trajectories. However, the follicles isolated from older and heavier mice and those in diestrus had altered hormone profiles. These follicles contained oocytes with reduced meiotic competence and produced oocytes with greater spindle defects. CONCLUSIONS: These results suggest that the original physical environment of the follicle within the ovary can impact its function when isolated and cultured. These findings are valuable as we begin to use in vitro follicle growth technology for a heterogeneous fertility preservation patient population.