ODF2L is a negative regulator of ciliogenesis

The centrosome is a subcellular organelle whose main role is acting as a microtubule organising centre (MTOC). It consists of two barrel-shaped centrioles surrounded by the pericentriolar matrix. Further out are electron-dense protein particles called centriolar satellites. In quiescent cells, centrioles migrate to the apical surface of the cell and act as the template (basal body) for hair-like projections called cilia and flagella. Control of ciliogenesis is still not fully understood. Here, I have studied three proteins to determine their contribution to ciliogenesis: zebrafish Cep72 and Odf2b, and human ODF2L. Human CEP72 has been previously identified as a PCM-1 interacting centriolar satellite protein which contributes to ciliogenesis in cultured cells. I tested whether Cep72 depletion in zebrafish embryos would disrupt ciliogenesis and cause a developmental phenotype. A ‘ciliary’ phenotype was observed, consisting of the typical morphology following ciliary disruption, yet with no obvious change in cilium numbers or length.

ODF2 is a component of the distal appendages of the mother centriole, shown previously to regulate ciliogenesis. Related proteins include human ODF2L and zebrafish Odf2a and Odf2b. Here, I show that depletion of odf2b led to reduced cilium length in the zebrafish embryo pronephros. I also observed localisation of ODF2L to the centriolar satellites in proliferating cells in culture, using immunofluorescence-labelling. Intriguingly, at the onset of ciliogenesis ODF2L disappeared from centriolar satellites but then reappeared after ciliation was complete. Overexpression of ODF2L in cultured cells suppressed ciliogenesis, even after initiation of ciliation by serum deprivation. Furthermore, ODF2L knockdown resulted in cilia being formed in cells cultured in serum-supplemented media, when they would not normally produce cilia. Pull-down of ODF2L-interacting partners and identification with mass spectrometry, coupled with in silico structural analysis, suggest that ODF2L may be involved in Golgi trafficking to the cilium which is necessary for ciliogenesis to begin.