Antral follicles develop in xenografted cryopreserved african elephant (Loxodonta africana) ovarian tissue

The preservation of germ plasm from endangered species could augment captive breeding programs aimed at maintaining genetic diversity. Mammalian female germ plasm (oocytes) is extremely difficult to collect and cryopreserve; however, a promising alternative is the cryopreservation of ovarian tissue. In the present study, athymic nude (nu/nu) Balb/C mice were used to evaluate in vivo viability of cryopreserved ovarian tissue from Institute of Cancer Research genotype (ICR) mice or elephants. Female mice were ovariectomized prior to transplant of cryopreserved-thawed ovarian tissue from ICR mice (n=4) or elephants (n=6). Control mice were sham operated (n=4) or ovariectomized (n=5). Transplants were in the ovarian bursa, enabling in vivo ovulation and pregnancies from allografts. Vaginal cytology was monitored daily, and the intervals between and duration of epithelial cells present in smears were evaluated. Appearance of epithelial cells in sham-operated and allografted mice were at intervals of 4.3±0.6 and 3.3±0.5 days, lasting for 1.4±0.1 and 1.6±0.2 days, respectively. Sporadic incidence of epithelial cells in ovariectomized animals occurred at longer intervals (8.6±3.8 days). Females with xenografted elephant ovarian tissue demonstrated epithelial cells in vaginal smears at intervals of 4.5±1.0 days, for 2.5±0.5 days duration, which was significantly longer than the other groups (P<0.05). Histological evaluation of tissues at the time of epithelial cells in smears demonstrated well-developed antral follicles, although oocytes were of poor morphological appearance or only cumulus-like complexes were seen. The nude mouse model is effective for assessing cryopreserved ovarian tissue xenograft function which can support the development of antral follicles.