Two Structural Variants of Nek2 Kinase, Termed Nek2A and Nek2B, Are Differentially Expressed inXenopusTissues and Development

Abstract

Nek2 kinase, a NIMA-related kinase, has been suggested to play both meiotic and mitotic roles in mammals, but its function(s) during development is poorly understood. We have isolated here cDNAs encoding aXenopushomolog of mammalian Nek2 and have shown thatXenopusNek2 has two structural variants, termed Nek2A and Nek2B. Nek2A, most likely a C-terminally spliced form, corresponds to the previously described human and mouse Nek2, while Nek2B is most probably a novel, C-terminally unspliced form of Nek2. As a consequence of this (probable) alternative splicing, Nek2B lacks the C-terminal 70-amino-acid sequence of Nek2A, which contains a PEST sequence (or a motif for rapid degradation). Western blot analysis reveals that Nek2A is expressed predominantly in the testis (presumably in spermatocytes) and very weakly in the stomach and, during development, only after the neurula stage. By contrast, Nek2B is expressed mainly in the ovary and in both primary and secondary oocytes and early embryos up to the neurula stage. These results suggest that Nek2A and Nek2B may play both meiotic and mitotic roles, but in a spatially and temporally complementary manner duringXenopusdevelopment, and that Nek2B, rather than Nek2A (or the conventional form of Nek2), may play an important role in early development. We discuss the possibility that a counterpart ofXenopusNek2B might also exist and function in early mammalian development.