The end of a monolith: Deconstructing the Cnn-Polo interaction.
In Drosophila melanogaster a functional pericentriolar matrix (PCM) at mitotic centrosomes requires Centrosomin-Long Form (Cnn-LF) proteins. Moreover, tissue culture cells have shown that the centrosomal localization of both Cnn-LF and Polo kinase are co-dependent, suggesting a direct interaction. Our recent study found Cnn potentially binds to and is phosphorylated by Polo kinase at 2 residues encoded by Exon1A, the initiating exon of a subset of Cnn isoforms. These interactions are required for the centrosomal localization of Cnn-LF in syncytial embryos and a mutation of either phosphorylation site is sufficient to block localization of both mutant and wild-type Cnn when they are co-expressed. Immunoprecipitation experiments show that Cnn-LF interacts directly with mitotically activated Polo kinase and requires the 2 phosphorylation sites in Exon1A. These IP experiments also show that Cnn-LF proteins form multimers. Depending on the stoichiometry between functional and mutant peptides, heteromultimers exhibit dominant negative or positive trans-complementation (rescue) effects on mitosis. Additionally, following the completion of meiosis, Cnn-Short Form (Cnn-SF) proteins are required for polar body formation in embryos, a process previously shown to require Polo kinase. These findings, when combined with previous work, clearly demonstrate the complexity of cnn and show that a view of cnn as encoding a single peptide is too simplistic.
a Department of Biology , Indiana University , Bloomington , IN , USA.
Robert C
RC
Eisman
a Department of Biology , Indiana University , Bloomington , IN , USA.
Melissa A S
MA
Phelps
a Department of Biology , Indiana University , Bloomington , IN , USA.
Thomas C
TC
Kaufman
D000595:Amino Acid Sequence; D000818:Animals; D018385:Centrosome / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D018398:Homeodomain Proteins / Q000737:chemistry / Q000378:metabolism*; D008938:Mitosis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; C098130:cnn protein, Drosophila; C072004:polo protein, Drosophila; D017346:Protein Serine-Threonine Kinases
Centrosome; Drosophila; Polar body; Polo kinase; centrosomin (cnn); cleavage mitosis; meiosis; multimers; protein-protein interaction