Two structural variants of Nek2 kinase, termed Nek2A and Nek2B, are differentially expressed in Xenopus tissues and development

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 po orly understood. We have isolated here cDNAs encoding a Xenopus homolog of mammalian Nek2 and have shown that Xenopus Nek2 has two structural variants , termed Nek2A and Nek2B. Nek2A, most likely a C-terminally spliced form, c orresponds to the previously described human and mouse Nek5 while Nek2B is most probably a novel, C-terminally unspliced form of Nek2. As a consequenc e of this (probable) alternative splicing, Nek2B lacks the C-terminal 70-am ino-acid sequence of Nek2A, which contains a PEST sequence (or a motif for rapid degradation). Western blot analysis reveals that Nek2A is expressed p redominantly in the testis (presumably in spermatocytes) and very weakly in the stomach and, during development, only after the neurula stage. By cont rast, Nek2B is expressed mainly in the ovary and in both primary and second ary oocytes and early embryos up to the neurula stage. These results sugges t that Nek2A and Nek2B may play both meiotic and mitotic roles, but in a sp atially and temporally complementary manner during Xenopus development, 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 of Xenopus Nek2B might also exist and function in early mammali an development. (C) 1999 Academic Press.