As a major microtubule-organizing center in mammalian cells, the centrosome comprises of a pair of centrioles that are connected by a fibrous linker and surrounded by the pericentriolar material (PCM). As a motile organelle in animal cells, the centrosome often migrates within the cytoplasm, which depends on microtubules and actin filaments. Many cellular processes require centrosome movement, including centrosome separation before spindle assembly, membrane docking of basal body before cilia formation, centrosome re-positioning in cell polarization during cell migration and so on. However, the regulation of centrosome motility remains largely unknown. On the other hand, GAS2L1, an actin-microtubule binding protein, was identified as an, SxIP motif containing, EB1 binding protein in a...[ Read more ]

As a major microtubule-organizing center in mammalian cells, the centrosome comprises of a pair of centrioles that are connected by a fibrous linker and surrounded by the pericentriolar material (PCM). As a motile organelle in animal cells, the centrosome often migrates within the cytoplasm, which depends on microtubules and actin filaments. Many cellular processes require centrosome movement, including centrosome separation before spindle assembly, membrane docking of basal body before cilia formation, centrosome re-positioning in cell polarization during cell migration and so on. However, the regulation of centrosome motility remains largely unknown. On the other hand, GAS2L1, an actin-microtubule binding protein, was identified as an, SxIP motif containing, EB1 binding protein in a recent proteomic study and exhibited F-actin, microtubule and microtubule plus end localizations. Interestingly, in our study, GAS2L1 was also found to localize to the proximal end of centrioles and involve in regulating centrosome motility by recruiting microtubules to centrioles in an EB1-dependent manner. RNAi-based depletion of GAS2L1 impairs centriole motility and reduces microtubules attachment onto centrioles, suggesting that GAS2L1 can modulate forces applied on and thus motility of centrioles by attaching microtubules on them. More importantly, GAS2L1 are required in the first step of centrosome separation, known as centrosome disjunction. RNAi-based depletion of GAS2L1 introduces defects in centrosome disjunction, whereas overexpression of GAS2L1 causes premature centrosome separation. We also showed that the relative expression level of GAS2L1 and centrosome linker determines the distance between the two centrosomes, suggesting there are counteracting forces acting on centrosomes modulated by GAS2L1 and centrosome linker protein at different stages of the cell cycle. In addition, we found that GAS2L1 is a phosphorylated protein and the activity of GAS2L1 triggering centrosome separation can be regulated by phosphorylations. One of the candidate kinases to act on GAS2L1 is Nek2A, which is the most important kinase functionally implicated in centrosome disjunction. Based on these findings, we propose a new model of centrosome disjunction to provide new insights on the regulation of centrosome motility during in centrosome cycle.