An international research team, including scientists from TalTech, unexpectedly discovered a new type of follicle while investigating fertility preservation possibilities for young cancer patients. These so-called support follicles, which do not develop viable eggs, play an important role in supporting the follicles that do and may change the understanding of fertility preservation. The results of the study were published in Nature Communications.
The removal and freezing of ovarian tissue is currently the best way to preserve fertility in female cancer patients, as the chemotherapy or radiotherapy used in cancer treatment would destroy the developing oocytes. Women do not produce new oocytes during their lifetime. The best-known way to preserve fertility in adult women is to remove and freeze ovarian tissue before starting treatment. The central question of the study was whether the same method could work for girls who have not yet reached puberty and whose ovaries have not yet fully developed.
Follicles are structures where the oocyte is surrounded by granulosa cells, whose role is to support the maturation of the oocyte and regulate its release. The scientists compared 120 follicles equally distributed between adults and children, investigating which genes are expressed in follicles at different developmental stages. Surprisingly, the scientists found that the follicles were divided into two groups. Agne Velthut-Meikas, associate professor at TalTech and co-author of the study, explains the discovery: “Most of the follicle development proceeded as expected, showing gene expression patterns characteristic of both the oocyte and granulosa cells. However, about a third of the studied follicles, so-called “support follicles,” lacked any gene expression typical of oocytes. It was impossible to distinguish between follicles containing active and passive oocytes visually under a microscope.”
The scientists showed that the role of the granulosa cells in the supporting follicles is to promote the growth of those follicles that contain actively developing oocytes.
According to one of the study’s partners, Andres Salumets, board member of the Competence Center on Health Technologies (Celvia CC), the new knowledge will certainly change how a woman’s fertility and egg reserve are assessed. This, in turn, will help improve fertility preservation methods for cancer patients, allowing them to have children after recovering from cancer.
However, whether the exclusive use of oocytes from active follicles in fertility treatments such as in vitro fertilization, will improve the success rate of fertility treatments, which is 30%, remains to be seen in future studies.
Reference:
Rooda, I., Hassan, J., Hao, J. et al. In-depth analysis of transcriptomes in ovarian cortical follicles from children and adults reveals interfollicular heterogeneity. Nat Commun 15, 6989 (2024). https://doi.org/10.1038/s41467-024-51185-0