Development of Goat Embryos Reconstituted with Somatic Cells: the Effect of Cell-Cycle Coordination between Transferred Nucleus and Recipient Oocytes

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The developmental ability and the nucleus and microtubule dynamics of nuclear transplanted goat embryos derived from in vitro matured oocytes were studied while controlling cell-cycle coordination of donor embryonic nuclei and recipient cytoplasts. Three groups of transfers were studied: G0/G1 (after the fibroblast cells grew to 100% confluence) and G2/M (nocodazole treated) phase fibroblasts transferred to MII cytoplasts (G0/G1→MII and G2/M→MII group, respectively), and G0/G1 phase fibroblasts transferred to preactivated cytoplasts, mostly at S-phase, (G0/G1→Pre group) by electrical fusion. The results showed that fusion and developmental ability did not differ between G0/G1→MII and G0/G1→Pre groups. However the developmental rate of embryos in the G0/G1→MII group was significantly higher than that of the G2/M→MII group. Most fibroblast nuclei (G0/G1 and G2/M) transferred into MII oocytes underwent premature chromosome condensation (PCC). Normal spindle were only detected in the G0/G1→MII group. In contract, fibroblast nuclei in pre-activated oocytes rarely underwent PCC, but formed a swollen nuclear structure. The data suggest that in vitro matured goat oocytes can support the development of somatic fibroblasts after nuclear transfer, G0/G1 →MII and G0/G1→S nuclear transfer might be effective ways for improving the developmental competence of the reconstituted embryos, and that G2/M→MII nuclear transfer by electrical fusion (even in Ca²⁺-free fusion medium) induces abnormal chromosome ploidy.