Nek2 expression and localization in porcine oocyte during maturation.

We studied the role of the Ser/Thr protein kinase Nek2 on meiosis progression by using in vitro porcine oocyte maturation system. Nek2 is a candidate of a mammalian homologue of NIMA, which was found in Aspergillus nidulans as an essential molecule for mitosis progression. We cloned porcine Nek2 cDNA, and examined the mRNA and protein expression levels during meiosis progression. The expression levels did not change through the oocyte maturation, but fluorescence microscopy observation of Nek2 in the oocytes at various maturation steps showed that Nek2 was detected only at metaphase II, but not before metaphase II. At metaphase II, Nek2 was found exclusively on the chromosomes. These results suggest that Nek2 changes the cellular localization during maturation and accumulates on the chromosomes to play a role on the entry and progression of metaphase II.