Cryopreservation of Preantral Follicles

Abstract

In mammals, the total number of female germ cells is already established by the time of birth, meaning that no mitosis will take place in oogonias thereafter. Their cryostorage, therefore, depends on ovarian tissue manipulation. As an alternative to mature oocyte cryopreservation, the maintenance of inactive preantral follicles is a remarkable option because (i) their availability in the ovary is greater; (ii) as inactive and small structures, they show less sensitivity to cryoinjury and the toxic effects of cryoprotectants; and (iii) they are present in the gonads at all ages, allowing their retrieval from prepubertal individuals or even immediately postmortem. Nevertheless, some difficulties remain regarding their in vitro activation and development to the ovulatory stage. For this reason, the best option for their total development is transplantation back to the donor or between species, promoting follicle activation and development. This technique has proved its efficiency and led to several live births in both animals and humans. Since each species has its own particularities in terms of ovarian tissue composition, a number of protocols have been documented, which may be used for either isolated or in situ preantral follicles.

Human Ovarian Follicles Xenografted in Immunoisolating Capsules Survive Long Term Implantation in Mice

“…secondary/antral) follicles, as expected. More mature follicles contain oocytes that are more metabolically active and antral follicles contain the cumulusoocyte complex, resulting in decreased cryoprotectant agent penetration and therefore increased probability of ice crystal formation (38). Our observation that the stroma in slow frozen tissues (Figure 5) is less fibrous as compared to vitrified tissues (Figure 6) is somewhat unexpected since the literature indicates that vitrification typically has better stromal cell survival (37).…”

Bax/Bcl-2 expression ratio analysis of rat ovary vitrified with date juice concentrate as a natural extracellular cryoprotectant

“…Primordial and primary follicles are also located in the peripheral cortex, allowing them to respond better to cryoprotectants than other follicles. [ 4 42 ] In particular, primordial follicles are known to have follicular recovery ability after being damaged during vitrification. [ 43 ] However, the recovery mechanism cannot be explained definitively.…”

Microencapsulation and nanowarming enables vitrification cryopreservation of mouse preantral follicles

“…PAFs will suffer irreversible osmotic damage under high concentrations of CPAs, so the concentration of pCPAs was substantially reduced in this study compared to that of traditional vitrification cryopreservation of PAFs 43 . Since trehalose can increase cell viability after vitrification 44 , 1 M trehalose was added to the CPAs.…”