THE NIMA-RELATED KINASE-2, NEK2, IS EXPRESSED IN SPECIFIC STAGES OF THE MEIOTIC CELL-CYCLE AND ASSOCIATES WITH MEIOTIC CHROMOSOMES

The Aspergillus nimA gene encodes a Ser/Thr protein kinase which is re quired for mitosis, in addition to Cdc2, and which has been suggested to have a role in chromosomal condensation. In this study, we isolated a potential murine homologue of nimA, Nek2, which was shown to be exp ressed most abundantly in the testis of the adult tissues examined, It s expression in the testis was restricted to the germ cells, with high est levels detected in spermatocytes at pachytene and diplotene stages , Immunohistochemical analysis revealed that Nek2 localized to nuclei, exhibiting a nonuniform distribution within the nucleus, Nek2 appeare d to be associated with meiotic chromosomes, an association that was b etter defined by immunolocalization to hypotonically dispersed meiotic chromosomes. This localization was more apparent in regions of dense chromatin, including the sex vesicle, and was also obvious at some of the chromosome ends, The presence of Nek2 protein was not unique to ma le germ cells, as it was found in meiotic pachytene stage oocytes as w ell, Furthermore, in an in vitro experimental setting in which meiotic chromosome condensation was induced with okadaic acid, a concomitant induction of Nek2 kinase activity was observed, The expression of Nek2 in meiotic prophase is consistent with the hypothesis that in vivo, N ek2 is involved in the G(2)/M phase transition of the cell cycle, Our results further provide evidence that in vivo, mouse Nek2 is involved in events of meiosis, including but not limited to chromosomal condens ation.