668A Poster - 10. Cell biology: Cytoskeleton, organelles and trafficking
Thursday April 07, 2:00 PM - 4:00 PM

Authors:
Levente Kovacs ¹; Jennifer Chao-Chu ²; Sandra Schneider ²; Agnieszka Fatalska ^2,3; Magdalena M Richter ²; Emma Stepinac ⁴; Marco Gottardo ⁵; George Tzolovsky ²; Nikola S Dzhindzhev ²; Maria Giovanna Riparbelli ⁵; Giuliano Callaini ⁵; Michal Dadlez ³; Gang Dong ⁴; David M Glover ^1,2

Affiliations:
1) Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA; 2) Department of Genetics, University of Cambridge, UK; 3) Laboratory of Mass Spectrometry, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland; 4) Max Perutz Labs, Vienna BioCenter, Vienna, Austria; 5) Department of Life Sciences, University of Siena, Siena, Italy

Keywords:
i. cellular organelles; d. centrosome

Centrioles are evolutionarily conserved organelles required to assure the fidelity of cell division, motility and signaling. Although the majority of key proteins ensuring proper centriolar structure, duplication and maturation have been described, several new candidates have emerged from protein interaction studies. In a search for interacting partners of the core centriole cartwheel protein, Sas6, of Drosophila, we recently identified Gorab, better known as a Golgi protein mutated in the human disease Gerodermia osteodisplastica. We discovered that Gorab is a moonlighting protein – whereas dimeric Gorab localizes to the trans-Golgi, monomeric Gorab directly interacts with Sas6 dimers at the centriole’s core where it is essential for centriole duplication and symmetry. Here we show that Gorab’s high binding affinity to the limited amount of centriolar Sas6 is a key determinant of Gorab’s localization. Thus, upon Gorab overexpression, there is no increase in its levels at centrioles and the surplus Gorab associates with the trans-Golgi. Meiotic spermatocytes are particularly sensitive and moderate Gorab overexpression results in a Golgi-related cytokinesis defect and consequently male sterility. Upon Sas6 overexpression, however, the amount of Gorab dramatically increases both in the centrioles and in non-centriolar Sas6 aggregates and Golgi-associated Gorab decreases. Moreover, targeting elevated levels of Sas6 to mitochondria re-localizes endogenous Gorab to this organelle while depleting Gorab at the Golgi. In line with these observations, in vitro interaction assays reveal that Sas6 can disrupt preformed Gorab homodimers and disassociate Gorab from its Golgi-associated interactor Rab6. Strikingly, Sas6 overexpression can rescue the cytokinesis defects of Gorab-overexpressing males and restore their fertility. Thus, the high affinity of the Sas6 dimer for Gorab monomers ensures that Gorab gives priority to its moonlighting function at the centriole allowing remaining Gorab to dimerize and localize to the Golgi for its official duties.