title: The NIMA-related kinase X-Nek2B is required for efficient assembly of the zygotic centrosome in Xenopus laevis.
abstract: Nek2 is a mammalian cell cycle-regulated serine/threonine kinase that belongs to the family of proteins related to NIMA of Aspergillus nidulans. Functional studies in diverse species have implicated NIMA-related kinases in G(2)/M progression, chromatin condensation and centrosome regulation. To directly address the requirements for vertebrate Nek2 kinases in these cell cycle processes, we have turned to the biochemically-tractable system provided by Xenopus laevis egg extracts. Following isolation of a Xenopus homologue of Nek2, called X-Nek2B, we found that X-Nek2B abundance and activity remained constant through the first mitotic cycle implying a fundamental difference in Nek2 regulation between embryonic and somatic cell cycles. Removal of X-Nek2B from extracts did not disturb either entry into mitosis or the accompanying condensation of chromosomes providing no support for a requirement for Nek2 in these processes at least in embryonic cells. In contrast, X-Nek2B localized to centrosomes of adult Xenopus cells and was rapidly recruited to the basal body of Xenopus sperm following incubation in egg extracts. Recruitment led to phosphorylation of the X-Nek2B kinase. Most importantly, depletion of X-Nek2B from extracts significantly delayed both the assembly of microtubule asters and the recruitment of gamma-tubulin to the basal body. Hence, these studies demonstrate that X-Nek2B is required for efficient assembly of a functional zygotic centrosome and highlight the possibility of multiple roles for vertebrate Nek2 kinases in the centrosome cycle.
authors.affiliation: Department of Biochemistry, University of Leicester, Adrian Building, University Road, Leicester LE1 7RH, UK. amf5@le.ac.uk.
authors.forename: A M
authors.initials: AM
authors.lastname: Fry
authors.forename: P
authors.initials: P
authors.lastname: Descombes
authors.forename: C
authors.initials: C
authors.lastname: Twomey
authors.forename: R
authors.initials: R
authors.lastname: Bacchieri
authors.forename: E A
authors.initials: EA
authors.lastname: Nigg
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D018797:Cell Cycle Proteins; D018385:Centrosome / Q000201:enzymology*; D002843:Chromatin / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D008297:Male; D008938:Mitosis / Q000502:physiology; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism*; D013094:Spermatozoa / Q000201:enzymology; D029867:Xenopus Proteins; D014982:Xenopus laevis; D015053:Zygote / Q000201:enzymology
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D029867:Xenopus Proteins; C490316:NEK2 protein, Xenopus; C490315:Nek2B protein, Xenopus; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; C442331:NIMA-related kinase 6; D017346:Protein Serine-Threonine Kinases