Mice thrive without Cdk4 and Cdk2

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mammalian cell division relies on sequential activation of Cyclin-dependent kinases (Cdks), primarily Cdk4, Cdk6, Cdk2, and Cdk1.
• Viable mice lacking individual Cdk4, Cdk6, or Cdk2 suggest compensatory roles among these kinases.

Purpose of the Study:

• To investigate the necessity of Cdk4 and Cdk2 in mammalian cell cycle regulation and organismal homeostasis.
• To elucidate the functional redundancy or essentiality of Cdk4 and Cdk2 during embryonic development and adult life.

Main Methods:

• Generation and analysis of mice with combined genetic deficiencies in Cdk4 and Cdk2.
• Conditional ablation of Cdk2 in adult Cdk4-deficient mice.
• Assessment of survival, physiological function, and cell cycle kinetics in mutant mice and embryonic fibroblasts.

Main Results:

• Mice lacking both Cdk4 and Cdk2 (Cdk4(-/-);Cdk2(-/-)) survived embryonic development but died shortly after birth, suggesting a critical role during this period.
• Conditional deletion of Cdk2 in adult Cdk4-deficient mice did not cause apparent abnormalities, and these mice recovered normally from partial hepatectomy.
• Cdk4(-/-);Cdk2(-/-) embryonic fibroblasts exhibited immortalization, robust pRb phosphorylation, and normal S phase kinetics in culture.

Conclusions:

• Cdk4 and Cdk2 are dispensable for the progression of the mammalian cell cycle in cultured cells and for maintaining adult homeostasis.
• The combined absence of Cdk4 and Cdk2 leads to embryonic lethality, indicating essential roles during development that are compensated for in adult tissues.
• These findings challenge the established view of Cdk4 and Cdk2 as universally essential drivers of the cell cycle in mammals.