The CK1 group of eukaryotic protein kinases are composed of seven CK1 isoforms (CK1α, CK1α2, CK1δ, CK1ε, CK1γ1, CK1γ2, and CK1γ3), two Tau–tubulin kinase isoforms (TTBK1 and TTBK2), and three VRK isoforms (VRK1, VRK2, and VRK3)