Cdk2 Conditional Knockout mouse — Rosa26-CreERT2 pairing

Cdk2, the mouse ortholog of human CDK2, encodes the cyclin dependent kinase that partners cyclin E in late G1 and cyclin A in S phase, requiring CAK phosphorylation of threonine 160 in the activation loop and inhibition by p21 and p27, and phosphorylating RB, p27 itself, CDC6, NPAT and nucleophosmin to coordinate origin licensing, histone synthesis and centrosome duplication. Loss of function is surprisingly tolerated because CDK1 binds cyclin E and cyclin A and executes S phase entry, so null mice are viable and only sterile from meiotic prophase failure at the telomere attachment step, a phenotype that makes this a clean reproductive biology model. That redundancy sets the design logic: conditional nulls are best for germ cell and CCNE1 amplified synthetic lethality studies, whereas analog-sensitive gatekeeper knockins allow acute chemical genetic inhibition that outperforms genetic deletion. Combine with Ccne1 or Ccne2 alleles when the endpoint is replication stress rather than proliferation, and pair with a germline or tumor-restricted Cre.

Tissue restricted knockout of Cdk2 keeps wild type function everywhere else. Breeding is often more robust, and the setup mirrors patient biology where mutations arise in a subset of cells. For stem cell work, plan Cre specificity, reporter crosses, and baseline phenotyping before you scale.