Follicular right shift: Xenografting queens' ovarian tissue into severe combined imunnodeficiency mice and its responses to exogenous gonadotropin

Ovarian xenografting is an auxiliary reproductive technique that allows the conservation of germplasm of high-value livestock and endangered species. The use of exogenous gonadotropins assists in developing xenografted tissues and obtaining viable follicles for in vitro embryo production; however, this use has not been reported in the xenografting of cats' (Felis catus) ovaries with C57BL/6 female SCID mice (Mus musculus) as recipients. Therefore, the aim of this study was to evaluate the responses of queens' ovaries to eCG when grafted into C57BL/6 female SCID mice. Ovarian cortex fragments from queens were grafted under the kidney capsule of 15 C57BL/6 SCID mice after bilateral ovariectomy. After 45 days, the recipients were divided into two groups: those that did not receive hormone induction (eCG−), which were euthanized at the time of induction, and those that received hormonal induction (eCG+), which were euthanized 48 hours later. All the tissues collected were histologically processed. The proportions of the different ovarian follicles were compared by chi-square test. The morphology of the follicles was compared between the experimental groups by Tukey (primordial, primary, and secondary follicles) and Kruskal–Wallis (antral follicles) tests. Macroscopically, we observed a few antral follicles that were over 1 mm in size in grafts treated with eCG. Microscopically, follicles of all categories were observed in the grafts, and all had normal morphology for the species studied. However, larger primordial and primary follicles were observed in the eCG+ transplants than those in the eCG− transplants. There was a decrease in primordial follicles and an increase in the other follicles, particularly in the antral follicles of the eCG+ group, a phenomenon that we propose to term “follicular right shift”. Luteinized follicles were also observed in grafts treated with eCG. Therefore, treatment with eCG is effective for follicular development but does not provoke a good superovulatory response, so the correct application time should be identified. Other protocols should be tested, to obtain viable follicles that can be used for in vitro embryo production.