The orderly progression of cell cycle depends on timely destruction of key regulators through ubiquitin-mediated proteolysis. The anaphase-promoting complex (APC) is a major component of this degradation machinery and its activation is regulated by CDC20 and CDH1. We demonstrate here that CDH1 mRNA is ubiquitously expressed in Xenopus embryos of all developmental stages. Loss of CDH1 function during early embryonic cell cycles leads to an immediate and prolonged arrest with low cyclin-dependent kinase activity. In contrast, ectopic overexpression of CDH1 induces cell cycle arrest during the first G, phase at the midblastula transition. CDH1-dependent degradation of cyclin A is likely involved in this G, arrest. Our findings establish the essential roles of CDH1 in embryonic cell cycles. (C) 2002 Elsevier Science (USA). All rights reserved.