Sangeeta Chauhan1,M. Kasim Diril1,*, Joanna H.S. Lee1, Xavier Bisteau1, Vanessa Manoharan1, Deepak Adhikari2,†, Chandrahas Koumar Ratnacaram1, Baptiste Janela3, Juliane Noffke1, Florent Ginhoux3,
Vincenzo Coppola4,‡, Kui Liu2, Lino Tessarollo4 and Philipp Kaldis1,5
1 A*STAR (Agency for Science, Technology and Research), Institute of Molecular and Cell Biology (IMCB), 61 Biopolis Drive, Proteos#3-09, Singapore 138673
2 Department of Chemistry and Molecular Biology, University of Gothenburg, SE-405 30 Gothenburg, Sweden
3 A*STAR (Agency for Science, Technology and Research), Singapore Immunology Network (SIgN), 8A Biomedical Grove, Immunos, Singapore 138648;
4 National Cancer Institute, Mouse Cancer Genetics Program, NCI-Frederick, Bldg. 560, 1050 Boyles Street, Frederick, MA 21702-1201, USA
5 Department of Biochemistry, National University of Singapore (NUS), Singapore 117597
* Present address: Izmir Biomedicine and Genome Institute, Dokuz Eylul University, 35340 Izmir, Turkey.
† Present address: School of Biomedical Sciences, Nursing and Health Sciences, Monash University, Clayton, VIC 3800, Australia.
‡ Present address: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, 988 Biomedical Research Tower, 460 West 12th Avenue, Columbus, OH 43210, USA.
Correspondence: Philipp Kaldis (email@example.com)
Published in Biochemical Journal on 12 September 2016.
Cyclin-dependent kinases (Cdks) control the eukaryotic cell cycle by phosphorylating serine and threonine residues in key regulatory proteins, but some Cdk family members may exert kinase-independent functions that cannot easily be assessed using gene knockout approaches. While Cdk2-deficient mice display near-normal mitotic cell proliferation due to the compensatory activities of Cdk1 and Cdk4, they are unable to undergo meiotic generation of gametes and are consequently sterile. To investigate whether Cdk2 regulates meiosis via protein phosphorylation or by alternative kinase-independent mechanisms, we generated two different knockin mouse strains in which Cdk2 point
mutations ablated enzyme activity without altering protein expression levels. Mice homozygous for the mutations Cdk2D145N/D145N or Cdk2T160A/T160A expressed only ‘kinasedead’ variants of Cdk2 under the control of the endogenous promoter, and despite exhibiting normal expression of cell cycle regulatory proteins and complexes, both mutations rendered mice sterile. Mouse cells that expressed only ‘kinase-dead’ variants of Cdk2 displayed normal mitotic cell cycle progression and proliferation both in vitro and
in vivo, indicating that loss of Cdk2 kinase activity exerted little effect on this mode of cell division. In contrast, the reproductive organs of Cdk2 mutant mice exhibited abnormal morphology and impaired function associated with defective meiotic cell division and inability to produce gametes. Cdk2 mutant animals were therefore comparable to gene knockout mice, which completely lack the Cdk2 protein. Together, our data indicate that the essential meiotic functions of Cdk2 depend on its kinase activity, without which the generation of haploid cells is disrupted, resulting in sterility of otherwise healthy animals.
Figure 5. Spermatocytes from Cdk2T160A and Cdk2D145N KI mice arrest during prophase I.
(A) Immunostaining with antibodies against the indicated markers on chromosome spreads from testes extracted of Cdk2T160/T160A mice at postnatal day 23. The merged images correspond to the staining of Sycp3 in red and the staining of indicated proteins above it. (B) Quantification of the percentage of spermatocytes identified in each stage of prophase I based on Sycp3 staining. Spermatocytes were extracted from testes of Cdk2+/+ (total cell count n = 317), Cdk2T160A/T160A (n = 338), and Cdk2D145N/D145N (n = 150) mice at postnatal day 23.
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