Figure 1. Immunodetection of early embryonic transcription.

Immunohistochemical detection of active RNAPII was performed with a commercially available monoclonal antibody against the Ser2 phosphorylated CTD of RNAPII (H5) and an Alexa 446 conjugated secondary antibody. (A-C) DAPI stained nuclei of a 16-cell stage embryo (A), 32-cell stage embryo (B) and a 100-cell stage embryo (C). An antibody signal was not detected in 16-cell stage embryos (A′). First signs of active transcription were visible in 32-cell stage embryos (B′) and fully active transcription was detected in 100-cell stage embryos (C′). Scale bar corresponds to 100 µm. In order to confirm the whole mount immunostainings, we performed a Western blot with protein extracts from 1-cell, 8-cell and 100-cell embryos (D). The 220 kDa phosphorylated RNAPII was detected only in the 100-cell stage protein extract (D′).