Fly centriole cartwheels without Cep135

Centrioles are complex microtubule (MT)-based structures that form two important cell organelles, the centrosome and the cilium or flagellum, and the dysfunction of these organelles has been linked to several human diseases. Cep135 (also known as Bld10) is a conserved centriolar protein that in some species is required for the formation of the central cartwheel, which initiates centriole duplication. However, flies lacking Cep135 are viable, suggesting that either Cep135 is not essential for cartwheel formation, or the cartwheel is not essential for centriole assembly in flies. Here (p. 5881), Jordan Raff and colleagues address this question using electron tomography (ET) and super resolution 3D structured illumination microscopy (3D-SIM) of mature fly spermatocytes. They find that, initially, relatively normal cartwheels form in daughter centrioles when Cep135 is absent, but these deteriorate over time and become more disorganised in mother centrioles. Detailed analysis of the cartwheel structure in the absence of Cep135 revealed that the localisation of the inner centriole components Sas-6 and Ana2 is perturbed, as well as of outer centriole factors, such as As1. Furthermore, the authors show that in wild-type cartwheels, Cep135 localises to a region between these inner and outer centriole components, suggesting that, in Drosophila, Cep135 has a role in the stabilisation of the cartwheel, and not in its formation.