NIMA was originally shown in Aspergillus nidulans to be necessary for entry into mitosis. NIMA-related mammalian proteins have since been identified as Nek1-4 and Nek6-9. High expression of Nek1 is seen in male and female germ cell lines of mice. Nek2 is the closest known mammalian relative to NIMA. Like NIMA, Nek2 expression peaks at the G2 to M phase transition. Nek3, Nek6, Nek7 and Nek9 also regulate mitosis. Nek1 and Nek8 have been linked with polycystic kidney disease, and Nek4 expression is present in most primary carcinomas. Nek7 localizes to the cytoplasm and is highly expressed in lung, testis, muscle, slpeen, heart, liver, leukocyte and brain. Lower expression of Nek7 is detected in the ovary, prostate and kidney, while no expression is seen in small intestine.