A Drosophila homologue of human Nek2: a kinase with centrosomal function. T. Moutinho-Santos 1, D. Perez-Mongiovi 1, M. Arajo 1, M. Costa 1, C. Gonzalez 2, C.E. Sunkel 1. 1) Instituto de Biolologia Molecular e Celular,Universidade do Porto, Porto, Portugal; 2) Eurpean Molecular Biology Laboratory, Cell Biology Program, Heidelberg, Germany.
During mitosis, duplicated chromosomes are segregated equally, ensuring genomic stability. For this, centrosome duplication and separtion must be tightly controlled. We have identified a cDNA clone that encodes a protein kinase structurally related to the human kinase Nek2. HNek2 is the closest homologue of the A.nidullans NIMA. HNek2 is a centrosomal kinase thought to be involved in centrosome separation in mammalian cells. The Drosophila and human proteins are highly homologous at the N-terminus, which encodes the serine/threonine kinase domain. At the C-terminus, several other structural domains known to be important for the function of the human protein are also present on the Drosophila homologue. These include two coiled-coil domains and an unusual leucine zipper. Immunolocalisation studies on SL2 cells and third larval instar neuroblasts show that DmNek2 localises to the spindle poles of mitotic cells. In interphase cells, one or two dots of labelling were also seen. DmNek2 co-localises with other centrosomal components, such as gama-tubulin and POLO. We have also constructed a DmNek2 mutant strain by mobilisation of a P-element inserted close to the promoter region. The mutant allele is a severe hypomorph, causes late larval lethality and strong mitotic phenotype. The most striking aspects of the mitotic phenotype includes abnormal anaphases, aneuploidy, premature sister chromatid separation and abnormal centrosome segregation. Quantification of mitotic parameters indicates that mutant cells do not enter mitosis as frequently as wild type cells and that if they do progression through mitosis is delayed in prophase. Taken together, our data suggest that we have identified the Drosophila homologue of the human Nek2 and that this centrosomal protein is essential for normal mitotic progression.