CDK1 and dry eye syndrome: On the contrary, the expression of cyclins Ccnd1/cyclin D1, Ccna1/cyclin A2, Ccnb1/cyclin B1 and B2, and of cyclin-dependent kinase 1 (Cdk1) was much stronger in KCs cultured for 1 week than in cells cultured for 3 weeks (Figure 4 and Supplementary Figure 8).