Senthil Raja Jayapal1, Chelsia Qiuxia Wang1,2, Xavier Bisteau1, Matias J. Caldez1,3, Shuhui Lim1, Vinay Tergaonka1,
Motomi Osato2, and Philipp Kaldis1,3
1 Institute of Molecular and Cell Biology, A*STAR Agency for Science, Technology and Research
2 Cancer Science Institute of
Singapore, National University of Singapore
3 National University of Singapore, Department of Biochemistry, Republic of Singapore
Published in Haematologica in April 2015.
Mouse knockouts of Cdk2 and Cdk4 are individually viable whereas the double knockouts are embryonic lethal
due to heart defects, and this precludes the investigation of their overlapping roles in definitive hematopoiesis.
Here we use a conditional knockout mouse model to investigate the effect of combined loss of Cdk2 and Cdk4 in
hematopoietic cells. Cdk2fl/flCdk4–/–vavCre mice are viable but displayed a significant increase in erythrocyte size.
Cdk2fl/flCdk4–/–vavCre mouse bone marrow exhibited reduced phosphorylation of the retinoblastoma protein and
reduced expression of E2F target genes such as cyclin A2 and Cdk1. Erythroblasts lacking Cdk2 and Cdk4 displayed
a lengthened G1 phase due to impaired phosphorylation of the retinoblastoma protein. Deletion of the
retinoblastoma protein rescued the increased size displayed by erythrocytes lacking Cdk2 and Cdk4, indicating
that the retinoblastoma/Cdk2/Cdk4 pathway regulates erythrocyte size. The recovery of platelet counts following
a 5-fluorouracil challenge was delayed in Cdk2fl/flCdk4–/–vavCre mice revealing a critical role for Cdk2 and Cdk4 in
stress hematopoiesis. Our data indicate that Cdk2 and Cdk4 play important overlapping roles in homeostatic and
stress hematopoiesis, which need to be considered when using broad-spectrum cyclin-dependent kinase inhibitors for cancer therapy.
Figure Legend:Cdk2 and Cdk4 regulate erythroid cell size. (A) Two-month oldCdk2fl/flCdk4–/–vavCre (DKO) and littermate wild-type (Control) mice are shown. (B) Complete blood count data for Cdk2fl/flCdk4–/–vavCre (DKO) mice (n=6) and littermate controls (n=6, wild-type or double heterozygotes) at two months of age. Two-tailed t-test results are indicated by asterisks; *P<0.05, **P<0.01, ***P<0.001. (C) Western blot analysis of total bone marrow (BM) from 4-month old Cdk2fl/flCdk4–/–vavCre (DKO) and littermate Cdk2+/+Cdk4+/+vavCre or Cdk2+/flCdk4+/-vavCre
control mice (Control) with the indicated antibodies. HSP90 and GAPDH served as loading controls.
For more information on Philipp KALDIS's laboratory, please click here.