Expression of the cyclin-dependent kinase inhibitor Dacapo is regulated byCyclin E

The Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) has been im plicated in mediating cell cycle arrest prior to terminal differentiation. In many instances, increased expression of CKIs immediately precedes mitoti c arrest. However, the mechanism that activates CKI expression in cells tha t are about to stop dividing has remained elusive. Here we have addressed t his issue by investigating the expression pattern of dacapo, a Cip/Kip CKI in Drosophila. We show that the accumulation of dacapo RNA and protein requ ires Cyclin E and that increased expression of Cyclin E can induce dacapo e xpression. We also show that the oscillation of the Cyclin E and Dacapo pro teins are tightly coupled during ovarian endocycles. Our results argue for a mechanism where Cyclin E/Cdk activity induces Dacapo expression but only within certain windows that are permissive for dacapo expression. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.