The International Journal of Developmental Biology

Int. J. Dev. Biol. 65: 487 - 496 (2021)

Vol 65, Issue 7-8-9

Mitotic timing is differentially controlled by A- and B-type cyclins and by CDC6 associated with a bona fide CDK inhibitor Xic1 in Xenopus laevis cell-free extract

Original Article | Published: 10 September 2021

Mohammed El Dika1, Lisa Wechselberger1, Bilal Djeghout1,3, Djamel Eddine Benouareth1,3, Krystyna Jęderka4, Sławomir Lewicki4,5, Robert Zdanowski6, Claude Prigent1,7, Malgorzata Kloc*,8,9,10 and Jacek Z. Kubiak*,1,2,4,11

1Univ Rennes, UMR 6290, CNRS, Institute of Genetics and Development of Rennes - IGDR, Cell Cycle Group, Faculty of Medicine, Rennes, France, 2Univ Rennes, UMR 6290, CNRS, Institute of Genetics and Development of Rennes - IGDR, Dynamics and Mechanics of Epithelia Group, Faculty of Medicine, Rennes, France, 3Biology Department, University 8 mai 1945, Guelma, Algeria, 4Department of Regenerative Medicine and Cell Biology, Military Institute of Hygiene and Epidemiology (WIHE), Warsaw, Poland, 5Department of Molecular Biology, Institute of Genetics and Animal Biotechnology, Polish Academy of Sciences, Jastrzebiec, Magdalenka, Poland, 6Laboratory of Molecular Oncology and Innovative Therapies, Military Institute of Medicine - WIM, Warsaw, Poland, 7CRBM, UMR 5237, CNRS, Université de Montpellier, Cell Cycle Group, Montpellier, France, 8The Houston Methodist Research Institute, Houston, Texas, USA, 9The Houston Methodist Hospital, Department of Surgery, Houston, Texas, USA, 10The University of Texas, M.D. Anderson Cancer Center, Department of Genetics, Houston Texas, USA, 11Departement of Experimental Embryology, Institute of Genetics and Animal Biotechnology, Polish Academy of Sciences, Jastrzębiec, Magdalenka, Poland


The timing of the M-phase is precisely controlled by a CDC6-dependent mechanism inhibiting the mitotic histone H1 kinase. Here, we describe the differential regulation of the dynamics of this mitotic kinase activity by exogenous cyclin A or cyclin B in the Xenopus laevis cycling extracts. We show that the experimental increase in cyclin A modifies only the level of histone H1 kinase activity, while the cyclin B increase modifies two parameters: histone H1 kinase activity and the timing of its full activation, which is accelerated. On the other hand, the cyclin A depletion significantly delays full activation of histone H1 kinase. However, when CDC6 is added to such an extract, it inhibits cyclin B-associated histone H1 kinase, but does not modify the mitotic timing in the absence of cyclin A. Further, we show via p9 co-precipitation with Cyclin-Dependent Kinases (CDKs), that both CDC6 and the bona fide CDK1 inhibitor Xic1 associate with the mitotic CDKs. Finally, we show that the Xic1 temporarily separates from the mitotic CDKs complexes during the peak of histone H1 kinase activity. These data show the differential coordination of the M-phase progression by cyclin A- and cyclin B-dependent CDKs, confirm the critical role of the CDC6-dependent histone H1 kinase inhibition in this process, and show that CDC6 acts differentially through the cyclin B- and cyclin A-associated CDKs. This CDC6- and cyclins-dependent mechanism likely depends on the precisely regulated association of Xic1 with the mitotic CDKs complexes. We postulate that: i. the dissociation of Xic1 from the CDKs complexes allows the maximal activation of CDK1 during the M-phase, ii. the switch between cyclin A- and cyclin B-CDK inhibition upon M-phase initiation may be responsible for the diauxic growth of mitotic histone H1 kinase activity.


Mitosis, cyclin, CDK1, CDC6, Xic1

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