title: TAC-1 and ZYG-9 form a complex that promotes microtubule assembly in C. elegans embryos.
abstract: BACKGROUND
  Modulation of microtubule dynamics is crucial for proper cell division. While a large body of work has made important contributions to our understanding of the mechanisms governing microtubule dynamics in vitro, much remains to be learned about how these mechanisms operate in vivo.
  
  
  RESULTS
  We identified TAC-1 as the sole TACC (Transforming Acidic Coiled Coil) protein in C. elegans. TAC-1 consists essentially of a TACC domain, in contrast to the much larger members of this protein family in other species. We find that tac-1 is essential for pronuclear migration and spindle elongation in one-cell-stage C. elegans embryos. Using an in vivo FRAP-based assay, we establish that inactivation of tac-1 results in defective microtubule assembly. TAC-1 is present in the cytoplasm and is enriched at centrosomes in a cell cycle-dependent manner. Centrosomal localization is independent of microtubules but requires the activity of gamma-tubulin and the Aurora-A kinase AIR-1. By conducting FRAP analysis in embryos expressing GFP-TAC-1, we find that centrosomal TAC-1 exchanges rapidly with the cytoplasmic pool. Importantly, we establish that TAC-1 physically interacts with ZYG-9, a microtubule-associated protein (MAP) of the XMAP215 family, both in vitro and in vivo. Furthermore, we also uncover that TAC-1 and ZYG-9 stabilize each other in C. elegans embryos.
  
  
  CONCLUSIONS
  Our findings identify TAC-1 as a core structural and functional member of the evolutionarily conserved TACC family of proteins and suggest that mutual stabilization between TACC and XMAP215 proteins is a key feature ensuring microtubule assembly in vivo.
authors.affiliation: Swiss Institute for Experimental Cancer Research (ISREC), CH-1066, Epalinges/Lausanne, Switzerland.
authors.forename: Jean Michel
authors.initials: JM
authors.lastname: Bellanger
authors.forename: Pierre
authors.initials: P
authors.lastname: Gönczy
mesh_terms: D000818:Animals; D015153:Blotting, Western; D017173:Caenorhabditis elegans / Q000196:embryology* / Q000378:metabolism; D002874:Chromosome Mapping; D036681:Fluorescence Recovery After Photobleaching; D005455:Fluorescent Antibody Technique; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D011233:Precipitin Tests; D034622:RNA Interference; D008941:Spindle Apparatus / Q000378:metabolism*
chemical_list: D008869:Microtubule-Associated Proteins