Figure 3

Proposed functions for Mps1 in centriole assembly. Studies with OAZ and Cetn2 suggest two functions for Mps1 in centriole assembly, an early function in procentriole assembly and a later function in centriole maturation that is mediated by Cetn2. We propose that the single centriolar focus of hSas6 observed upon overexpression of OAZ or hMps1KD represents an intermediate in centriole assembly (depicted as a red and blue sunburst, red indicating hSas6 and blue representing other cartwheel proteins). The observation that this structure is observed upon attenuation of Mps1 activity [29] suggests that Mps1 activity remodels this intermediate into cartwheels, onto which procentrioles are subsequently assembled. Because hMps1^Δ12/13 generates excess hSas6-containing structures in the absence of Cetn2 [28], this early function of Mps1 is presumably Cetn2-independent. The observation that Mps1 is required for the ability of Cetn2 to organize distal centriole elements [28] suggests that Mps1 has a second, Cetn2-dependent function in the maturation of centrioles. Structures and colors are as in Figure 1, with the exception of carets used to depict the centriolar appendages of the maternal centriole, and the sunburst depicting the hSas6-containing intermediate.