Expression of an S phase-stabilized version of the CDK inhibitor Dacapo can alter endoreplication.
In developing organisms, divergence from the canonical cell division cycle is often necessary to ensure the proper growth, differentiation, and physiological function of a variety of tissues. An important example is endoreplication, in which endocycling cells alternate between G and S phase without intervening mitosis or cytokinesis, resulting in polyploidy. Although significantly different from the canonical cell cycle, endocycles use regulatory pathways that also function in diploid cells, particularly those involved in S phase entry and progression. A key S phase regulator is the Cyclin E-Cdk2 kinase, which must alternate between periods of high (S phase) and low (G phase) activity in order for endocycling cells to achieve repeated rounds of S phase and polyploidy. The mechanisms that drive these oscillations of Cyclin E-Cdk2 activity are not fully understood. Here, we show that the Drosophila Cyclin E-Cdk2 inhibitor Dacapo (Dap) is targeted for destruction during S phase via a PIP degron, contributing to oscillations of Dap protein accumulation during both mitotic cycles and endocycles. Expression of a PIP degron mutant Dap attenuates endocycle progression but does not obviously affect proliferating diploid cells. A mathematical model of the endocycle predicts that the rate of destruction of Dap during S phase modulates the endocycle by regulating the length of G phase. We propose from this model and our in vivo data that endo S phase-coupled destruction of Dap reduces the threshold of Cyclin E-Cdk2 activity necessary to trigger the subsequent G-S transition, thereby influencing endocycle oscillation frequency and the extent of polyploidy.
Integrative Program for Biological and Genome Sciences, University of North Carolina, Chapel Hill, NC 27599, USA.
Christina I
CI
Swanson
Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Joy H
JH
Meserve
Curriculum in Bioinformatics & Computational Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Patrick C
PC
McCarter
Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Alexis
A
Thieme
Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Tony
T
Mathew
Curriculum in Bioinformatics & Computational Biology, University of North Carolina, Chapel Hill, NC 27599, USA Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA.
Timothy C
TC
Elston
Integrative Program for Biological and Genome Sciences, University of North Carolina, Chapel Hill, NC 27599, USA Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA Department of Genetics, University of North Carolina, Chapel Hill, NC 27599, USA duronio@med.unc.edu.
Robert J
RJ
Duronio
D000595:Amino Acid Sequence; D000818:Animals; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000378:metabolism*; D004064:Digestive System / Q000166:cytology / Q000196:embryology; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000196:embryology / Q000378:metabolism*; D062951:Endoreduplication; D000078404:Epidermal Cells; D005260:Female; D008938:Mitosis; D008954:Models, Biological; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D006080:Ovarian Follicle / Q000166:cytology; D059748:Proteolysis; D016196:S Phase; D012469:Salivary Glands / Q000166:cytology
D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; C103336:dap protein, Drosophila
CDK inhibitor; CRL4Cdt2; Cell cycle; Drosophila; Endocycle; Modeling; Polyploidy