In vitro and in vivo development of domestic cat embryos generated by in vitro fertilization after eCG priming and oocyte in vitro maturation.

The objective of this study was to evaluate, in the domestic cat, the effect of ovarian stimulation with eCG prior to oocyte in vitro maturation (priming) on in vitro and in vivo development after in vitro fertilization (IVF). For this purpose, oocyte donors were either 1) treated with a single dose of 200 IU eCG four days before oocyte recovery (eCG group), or, 2) given no treatment before oocyte recovery (control group). Ovaries of both groups were collected by ovariohysterectomy (OVH) and cumulus-oocyte complexes (COCs) were recovered by slicing. Immature COCs from both groups were matured in vitro (IVM) for 26-28 h. IVF was done with refrigerated epididymal sperm. After 24 h co-incubation, presumptive zygotes were cultured in vitro for eight days. The rates of cleavage, morulae, blastocyst development and hatching were estimated. Some blastocysts were stained for total cell counting and others were used for gene expression analysis of pluripotency (OCT4, SOX2 and NANOG) and differentiation markers (CDX2 and GATA6). Additionally, to evaluate in vivo development, embryos from the eCG group were transferred at Day 5 and Days 7 or 8 of IVC to synchronized cat recipients. The results showed that, eCG priming increased significantly the rate of blastocyst development as compared to the control group (37.9 and 25.6%, respectively) (P < 0.05). No differences were observed in total cell number of blastocysts and hatching blastocysts (mean ± SD) between the eCG and control groups (420.6 ± 193.6 and 347.0 ± 237.1, respectively) (P > 0.05). In the gene expression analysis, blastocysts generated in the eCG group had higher expression of OCT4 than blastocysts from the control group (P < 0.05). However, no significant differences were observed in the relative expression of SOX2, NANOG, CDX2 and GATA6 (P > 0.05). Additionally, six embryo transfer (ET) procedures were done, three with Day 5 embryos and three with Day 7 or 8 embryos. Recipients from both ET groups delivered live kittens. The total pregnancy rate was 4/6 (67%), meanwhile the live birth rate was 2/6 (33%). In conclusion, eCG priming improved the rate of blastocyst development in vitro and increased relative expression of OCT4. These results demonstrate that eCG priming of oocytes donors before IVM improves oocyte competence, enhance in vitro embryo development and allows live births of healthy offspring after ET.