ABSTRACT
The Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) has been implicated in mediating cell cycle arrest prior to terminal differentiation. In many instances, increased expression of CKIs immediately precedes mitotic arrest. However, the mechanism that activates CKI expression in cells that are about to stop dividing has remained elusive. Here we have addressed this issue by investigating the expression pattern of dacapo, a Cip/Kip CKI in Drosophila. We show that the accumulation of dacapo RNA and protein requires Cyclin E and that increased expression of Cyclin E can induce dacapo expression. We also show that the oscillation of the Cyclin E and Dacapo proteins 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.
Subject(s)
Cyclin E/metabolism , Cyclin-Dependent Kinases/antagonists & inhibitors , Drosophila Proteins , Gene Expression Regulation, Developmental , Insect Proteins/genetics , Nuclear Proteins/genetics , Animals , Cyclin E/genetics , Drosophila/embryology , Drosophila/genetics , Insect Proteins/metabolism , Mutagenesis , Nuclear Proteins/metabolismABSTRACT
In a screen for genes that interact with the Rap1 GTPase, we have identified a Drosophila gene, dacapo (dap), which is a member of the p21/p27 family of cdk inhibitors. Unlike mammalian cdk inhibitors studied to date, dap is essential for normal embryonic development. Dacapo inhibits cyclin-cdk activity in vitro. Overexpressing dap during eye development interferes with cell cycle progression and interacts genetically with the retinoblastoma homolog (Rbf) and cyclin E. dap expression in embryos parallels the exit of cells from the cell cycle. dap mutant embryos delay the normal cell cycle exit during development; many cells complete an additional cycle and subsequently become quiescent. Thus, dap functions during embryogenesis to achieve a precisely timed exit from the cell cycle.
Subject(s)
CDC2-CDC28 Kinases , Cell Cycle , Cyclin-Dependent Kinases/antagonists & inhibitors , Cyclins/antagonists & inhibitors , Drosophila Proteins , Drosophila melanogaster/embryology , Growth Inhibitors , Insect Proteins/physiology , Nuclear Proteins/physiology , Protein Kinases , Protein Serine-Threonine Kinases/antagonists & inhibitors , Amino Acid Sequence , Animals , Cloning, Molecular , Cyclin-Dependent Kinase 2 , Drosophila melanogaster/enzymology , Enzyme Inhibitors , Epidermal Cells , Eye/embryology , Gene Expression Regulation, Developmental , Genes, Insect , Genes, Lethal , Molecular Sequence Data , Mutagenesis, Insertional , Protein Kinase Inhibitors , RNA, Messenger/genetics , Sequence AlignmentABSTRACT
Cell proliferation and cell fate specification are under strict spatiotemporal control in the developing Drosophila eye. Cells excluded from five-cell preclusters synchronously enter a single additional cell cycle, the second mitotic wave, after which the remaining cells are sequentially recruited. When the second mitotic wave was blocked with the human cyclin-dependent kinase inhibitor p21CIP1/WAF1, each cell type was still specified. Hence, cell fate determination is regulated independently of the division pattern of precursor cells. However, the second mitotic wave is needed to generate appropriate numbers of each cell type. Moreover, p21 can arrest precursor cell proliferation and allow appropriate fate choice in vivo.
