126 EFFECTS OF THE REPRODUCTIVE STATUS ON DEVELOPMENTAL COMPETENCE OF RECIPIENT OOCYTES AFTER SOMATIC CELL NUCLEAR TRANSFER IN CAT

Abstract

The reproductive status of donor cat has been suggested to influence developmental competence of the oocytes after IVM/IVF (Karja et al. 2002 Theriogenology 57, 2289–2298). This study was conducted to examine the effect of the reproductive cycle stage of cat ovaries supplying recipient oocytes for nuclear transfer (NT) on the developmental competence of the oocytes after somatic cell nuclear transfer. Cat ovaries were collected at local veterinary clinics and stored at 35°C for a short period (1–6 h). Based on the presence or absence of follicles and corpora lutea, the ovarian pairs collected were classified into the inactive, follicular or luteal stages. Cumulus-oocyte complexes (COCs) were obtained from ovaries at each stage of the reproductive cycle by mincing/dissection and matured in vitro for 24 h, as previously described (Karja et al. 2002 Theriogenology 57, 2289–2298). In vitro matured oocytes from ovaries at the inactive (n = 114), follicular (n = 124), and luteal (n = 126) stages were mechanically enucleated in PBS supplemented with 5 μL mL⁻¹ of cytochalasin B and 3 mg mL⁻¹ BSA, and reconstructed with fibroblast cells derived from uterus tissue. The couplets were fused in Zimmerman medium with a single DC pulse of 1.5 kV cm⁻¹ for 50 μs. The successfully fused couplets were activated by a 5-min exposure to 10 μg mL⁻¹ calcium ionophore A23187 in MK1 medium (Kanda et al. 1998 J. Vet. Med. Sci. 60, 423–431) followed by 5 h of incubation in MK1 medium supplemented with 10 μg mL⁻¹ cycloheximide. The NT embryos were cultured in MK1 medium supplemented with 4 mg mL⁻¹ BSA at 38.0°C in a humidified atmosphere of 5% CO₂ in air. At 72 h of culture, all cleaved NT embryos were transferred to fresh MK1 medium supplemented with 5% fetal calf serum for an additional 4 days to evaluate their ability of development to the blastocyst stage. Data were analyzed by ANOVA. There were no significant differences (P > 0.05) among the fused oocytes derived from ovaries at the inactive, follicular, and luteal stages with respect to the percentages of cleavage (64.4%, 69.4%, and 74.5%, respectively) and blastocyst formation (17.4%, 21.0%, and 12.0%, respectively). These results indicate that the reproductive cycle stage of cat ovaries has no apparent effect on the development at competence of recipient oocytes after somatic cell nuclear transfer.