In situ hybridization of zebrafish corepressors in 8 cell embryos. To the left is expression of smrt and to the right is expression of ncor. This is at a time before the embryonic genome is turned on. Similar results for rar aa, rar ab, hdac3, rxr ga and rxr ab for 8 cell embryos and oocytes indicating that these necessary components for repression are present at fertilization. These are consistent with results of others identifying early embryonic expression of these genes (Bertrand et al., 2007) (Xu et al., 2009) (Waxman and Yelon, 2007). Using quantitative RT-PCR we have confirmed the presence of z smrt and z ncor in cDNAs from four separate 1–8 cell RNA extractions.