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Cryopreservation of preantral follicles is a promising technique to preserve female fertility. The aim of this study was to evaluate the effect of vitrification on the development of secondary follicles included in ovarian tissue or isolated after microdissection. An important end point included is the capacity of grown oocytes to resume meiosis. Sheep ovarian cortexes were cut into fragments and split into three different groups: (1) fresh (control): secondary follicles isolated without any previous vitrification; (2) follicle-vitrification (follicle-vit): secondary follicles vitrified in isolated form; and (3) tissue-vitrification (tissue-vit): secondary follicles vitrified within fragments of ovarian tissue ( in situ former) and subsequently subjected to isolation. From the three groups, isolated secondary follicles were submitted to IVC for 18 days. After IVC, cumulus-oocyte complexes (COCs) were harvested from follicles. As an additional control group, in vivo grown, in vivo -grown COCs were collected from antral ovarian follicles. All, recovered COCs were matured and the chromatin configuration was evaluated. Data were analyzed by ANOVA, and the means were compared by Student-Newman-Keuls test, and by chi-square. Differences were considered to be significant when P < 0.05. Isolated preantral follicles from all treatments had normal morphology, antrum formation, and low follicle degeneration after IVC. The growth rate between control and follicle-vit did not differ (P > 0.05), and was higher (P < 0.05) than for tissue-vit. The percentage of follicles that decreased diameter during IVC was significantly higher in tissue-vit than the in follicle-vit. Recovery rate of oocytes from normal follicles was higher in follicle-vit than in tissue-vit. Furthermore, oocyte viability was lower in tissue-vit than other treatments, and follicle-vit did not differ from control and in vivo grown. The percentage of oocytes meiosis resuming was not different between treatments except for in vivo grown. After vitrification, only follicle-vit showed metaphase I oocyte. We conclude that secondary follicles vitrified after isolation displayed a better follicular growth rate, oocyte viability, percentage of oocytes reaching the metaphase I stage, and fewer follicles with decreased diameter after IVC. [ABSTRACT FROM AUTHOR]

Abstract: The main objective was to compare the efficiency of vitrification techniques and solutions on the preservation of morphology, ultrastructure and viability of sheep preantral follicles enclosed in ovarian tissue fragments. The fragments were cryopreserved by using macrotube vitrification (MTV), solid-surface vitrification (SSV) or conventional vitrification (CV). These techniques were combined with one of the six solutions containing 6M ethylene glycol (EG) and with or without sucrose (SUC) (0.25 or 0.50M) and with or without fetal calf serum (FCS) (10%). After one week, samples were warmed and histological analysis was performed, showing that the percentage of normal follicles after CV (66.20±8.87%) using a solution containing 6M EG, 0.25M SUC and 10% FCS (vitrification solution 4 – VS4) was similar to fresh control (79.40±7.83%), MTV (53.40±10.60%) and SSV (56.75±15.33%), all of them with the same vitrification solution (P <0.05). For follicular viability evaluation, ovarian fragments were vitrified as described above. After warming, follicles were assessed by trypan blue dye. Controversially, the highest percentage of viable follicles was observed in MTV (97.06%) and was similar to fresh control (92.62%) (P <0.05), but was significantly different from SSV (81.08%) and CV (83.81%) (P <0.05). These results were validated by transmission electron microscopy that showed normal follicles observed in MTV and in fresh control. In addition, to verify the MTV with VS4 (a combination of the best technique plus the best solution), follicle viability was evaluated after 48h in vitro culture. The viability assay was performed by fluorescence microscopy (calcein-AM and ethidium homodimer-1) analysis as follows: follicles isolated from fresh tissue were forthwith analyzed or underwent 48h in vitro culture before analysis, whereas others fragments were vitrified/warmed and immediately analyzed or underwent 48h in vitro culture before analysis. These results showed that, although follicular viability after MTV/VS4 (65%) was reduced when compared to the non-vitrified follicles at day 0 (100%), follicular viability after MTV/VS4 at day 2 (36.5%) was similar to follicles vitrified at day 0 (65%) and similar to non-vitrified follicles at day 2 (62.5%) (P >0.05). As the decrease of viability in non-vitrified follicles at day 2 was similar to the decrease of MTV/VS4 in the same time, follicle viability at day 2 is not affected by MTV/VS4. In conclusion, using the experimental conditions of the present study, an efficient solution (VS4: 6M EG, 0.25M SUC and 10% FCS) and technique (MTV) were successfully used to vitrify ovine ovarian tissue. [Copyright &y& Elsevier]

Cryoinjuries caused by vitrification of tissues and organs lead to the loss of membrane proteins that mediate intercellular communications, such as connexins 37 (Cx37) and 43 (Cx43). Thus, the present study aimed to evaluate ovine Cx37 and Cx43 gene and protein expressions and developmental competence by in vitro –cultured secondary follicles retrieved from vitrified ovarian tissue. Ovarian fragments for the same ovary pair were distributed into six treatments: (1) fresh ovarian tissue (FOT); (2) vitrified ovarian tissue (VOT); (3) isolated follicles from fresh ovarian tissue (FIF); (4) isolated follicles from vitrified ovarian tissue; (5) isolated follicles from fresh ovarian tissue followed by in vitro culture (CFIF); (6) isolated follicles from vitrified ovarian tissue followed by in vitro culture (CVIF). In all treatments, Cx37 and Cx43 gene and protein expression patterns were evaluated by reverse transcription polymerase chain reaction and immunocytochemistry. In addition, secondary follicles were analyzed according to follicular integrity and growth, apoptosis, and cell proliferation. In vitro –cultured secondary follicles (CFIF and CVIF) were evaluated based on morphology (extruded follicles), antrum formation, and viability. The percentage of intact follicles was higher, whereas antrum formation, oocyte extrusion rate, and follicle viability were lower in CVIF than in CFIF treatment (P < 0.05). Terminal deoxynucleotidyl transferase–mediated biotinylated deoxyuridine triphosphates nick end-labeling assay demonstrated that apoptosis was absent in FIF, whereas follicles from all other treatments showed positive labeling. Cell proliferation index was higher in isolated follicles from vitrified ovarian tissue and CVIF treatments than in follicles from FIF. Expression of Cx43 messenger RNA was lower in CVIF treatment when compared with follicles from all other treatments (P < 0.05). Follicle Cx37 messenger RNA levels did not show alterations in any treatment (P > 0.05). Cx37 and Cx43 immunolabeling was localized mainly on granulosa cells and oocytes, respectively. In conclusion, isolation of ovine secondary follicles could be done successfully after vitrification of ovarian tissue, and the basement membrane integrity remained intact after in vitro culture. Although the gene and protein expression of Cx37 did not change after vitrification of ovarian tissue, Cx43 turned out to be altered in secondary follicles after vitrification and in vitro culture. [ABSTRACT FROM AUTHOR]