Fig. 3. The IIo appearance coincides with MBT. Embryos were allowed to develop at 23°C and analysed for RPB1 phosphorylation by western blot using the POL3/3 or the H5 antibody, or both. Batches of ten monospermic embryos (A) or polyspermic embryos (B) from the same female were sampled at the indicated hours post fertilisation (h.p.f.). The positions of the IIa, IIo and IIe forms are indicated.