The centrosome is the main microtubule-organizing center in animal cells. It comprises
of two centrioles and the surrounding pericentriolar material. Protein organization
at the outer layer of the centriole and outward has been studied extensively; however,
an overall picture of the protein architecture at the centriole core has been missing.
Here we report a direct view of Drosophila centriolar proteins at similar to 50-nm
resolution. This reveals a Sas6 ring at the C-terminus, where it overlaps with the
C-terminus of Cep135. The ninefold symmetrical pattern of Cep135 is further conveyed
through Anal-Asterless axes that extend past the microtubule wall from between the
blades. Ana3 and Rcd4, whose termini are close to Cep135, are arranged in ninefold
symmetry that does not match the above axes. During centriole biogenesis, Ana3 and
Rcd4 are sequentially loaded on the newly formed centriole and are required for centriole-to-centrosome
conversion through recruiting the Cep135-Ana1-Asterless complex. Together, our results
provide a spatiotemporal map of the centriole core and implications of how the structure
might be built.
