Gene activity and cleavage arrest in human pre-embryos

There is a high rate of spontaneous cleavage arrest around the four- to eight-cell stage of human developmentin vitro. Since this coincides with the time of activation of the embryonic genome it has been suggested that cleavage arrest may occur as a consequence of failure of gene activation. Gene expression in human pre-embryos is associated with an a-amanitin sensitive, qualitative change in protein synthesis. In order to ascertain the role of gene expression in cleavage arrest, we have examined the protein synthetic patterns of human pre-embryos which have undergone spontaneous cleavage arrest in vitro. Of 54 cleavage-arrested embryos, 27 demonstrated evidence of synthesis of proteins sensitive to α-amanitin, suggesting that cleavage arrest is not always accompanied by failure of activation of the genome. Our results would also suggest that activation of gene expression is simply related to neither cell number nor time spent in culture since fertilization, but may be related to continuing karyokinesis.