THE IN-VIVO EXPRESSION PATTERN OF MOUSE NEK2, A NIMA-RELATED KINASE, INDICATES A ROLE IN BOTH MITOSIS AND MEIOSIS

The human protein kinase Nek2 is related to the NIMA cell cycle regula tory kinase of Aspergillus nidulans. Whereas NIMA has been shown to be essential for cell cycle progression into mitosis in this fungus, the function of mammalian Nek2 remains to be elucidated. In this study, w e isolated a cDNA coding for a mouse ortholog of human Nek2 and analyz ed the expression of this kinase in different organs. RNase protection assays performed on RNAs from mouse adult organs showed very high exp ression of Nek2 in testis. Lower levels of transcripts were detected i n intestine, thymus, and skin, three mitotically active organs, and wh ole-mount in situ hybridization performed on 10.5-day embryos allowed the detection of Nek2 transcripts in the brain. In situ hybridization analysis of testis sections revealed that the transcription of Nek2 oc curred in a stage-specific manner during spermatogenesis. The stronges t signals were seen in cells undergoing meiosis, but Nek2 transcripts could also be detected in haploid cells (stage I and II spermatids). E xtending these results, in situ hybridization performed on ovary secti ons revealed strong signals in meiotically active oocytes. In addition , some Nek2 transcription was observed in actively dividing follicle c ells surrounding the oocytes and in the oviduct. Finally, indirect imm unofluorescence staining of testis sections with Nek2-specific antibod ies confirmed that this kinase is highly expressed in spermatocytes an d, to a lesser extent, in early spermatids. Taken together, these resu lts indicate that Nek2 may play an important role not only during mito sis but also during meiosis. (C) 1997 Academic Press.