What is a critical regulator of mitosis in all eukaryotic cells?

The critical regulator of mitosis in all eukaryotic cells are cyclin-dependent kinases (CDKs). These cyclins form complexes with S phase cyclins (S-CDKS) and mitotic cyclins (M-CDKS) to modulate DNA replication. S-CDK functions to prevent re-replication from occurring after the S phase is completed. M-CDK enables the transition of the cell into mitosis, and phosphorylates Cdc6 and Mcm proteins. The primary mitotic kinase in mitosis is CDK-1/cyclin B (which is a type of M-CDK). The CDK-1/cyclin B complex triggers the cell’s entry into mitosis by phosphorylating and activating enzymes which modulate chromatin condensation, spindle formation, and the breakdown of the nuclear envelope.