Fig. 2. Transplantation of nonreplicated, diploid 2n2c genomes into MII cytoplasts leads to rapid onset of premature spindles followed by chromosome segregation.

(A) Schematic of experiments interrogating premature cell division and chromosome segregation in diploid but nonreplicated (2n2c) somatic cell genomes. (B) Cell cycle analysis by flow cytometry of somatic cell nuclei labeled with propidium iodide. Majority of cumulus cells (right); or fibroblasts after serum starvation (lower left) were at the G₀/G₁ phase. (C) De novo metaphase spindle formation observed by live Oosight imaging 2 hours after SCNT. Scale bar, 10 μm. (D) Partitioning of transplanted 2n2c somatic genomes into a PB2 and a pronucleus after activation of SCNT oocytes. Left: DNA signal (Hoechst 33342). Middle: Bright-field (BF) image. Right: Merged images. Scale bar, 10 μm. (E) Rates of de novo premature metaphase spindle induction in SCNT oocytes followed by the PB2 extrusion and pronucleus formation. Bar plots show mean values derived from nine independent SCNT experiments with G₀/G₁ cumulus cells (mean of 70 SCNT oocytes per experiment, total 626 SCNT oocytes).