Comparison of developmental capacity for intra- and interspecies cloned cat (Felis catus) embryos

Interspecies nuclear transfer is an invaluable tool for studying nucleus-cytoplasm interactions; and at the same time, it provides a possible alternative to clone animals whose oocytes are difficult to obtain. In the present study, we investigated the possibility of cloning cat embryos using rabbit oocytes, and compared the developmental capacity; the timing of embryogenesis of the cat-rabbit cloned embryos with that of the cat-cat or the rabbit-rabbit cloned embryos. When cultured in M199, the rate of blastocyst formation of the cat-rabbit embryos was 6.9%, which was not significantly different than that of the cat-cat embryos (10.5%). However, the rate of blastocyst formation of rabbit-rabbit embryos (22.9%) was significantly greater than that of both the cat-rabbit and the cat-cat embryos (P < 0.05). The timing of the first three cleavages for the cat-rabbit embryos was similar to that of the rabbit-rabbit embryos, but significantly faster than that of the cat-cat embryos (P < 0.05), while the time to form blastocysts was similar to that of cat-cat embryos, but significantly slower than that of the rabbit-rabbit embryos (P < 0.05). Both M199 and SOF medium were evaluated for culturing cat-rabbit embryos; the rate of blastocyst formation in SOF (14.5%) was significantly greater than that in M199 (6.9%) (P < 0.05). These results demonstrate that: (1) the cat-rabbit embryos possess equal developmental capacity as cat-cat embryos; (2) the timing of the first three cleavages for the cat-rabbit embryos is recipient-specific, while the time to form blastocysts is donor nucleus-specific; and (3) SOF medium may be beneficial to overcome the morula-to-blastocyst block for cat-rabbit cloned embryos.