Primary cilia are microtubule-based sensory organelles that emerge from centrioles and can be found on almost all human cell types as a single hair-like protrusion. They communicate with the external environment by receiving external signals and stimuli, which are then transmitted into the cell via receptors and signalling proteins which are concentrated in the cilia. Unlike most of other organelles, cilium is not enclosed within membranes and requires a combination of transport, sorting and gating systems to maintain its distinct composition which is instrumental for its function and structure. Protein destined to the cilium can be divided into four major groups; integral membrane proteins, small soluble proteins, large soluble proteins and membrane-associated proteins.
In my talk I will introduce a molecular machinery that shuttles and sorts the membrane associated, lipid-modified, proteins to the cilium, thus contributing in maintaining its distinct composition. The mechanism involves the binding of the GDI-like solubilising factors UNC119a, UNC119b and PDE6D to the lipid-modified ciliary cargo and the specific release of the cargo in the cilia by the ciliary small G-protein Arl3 in a GTP-dependent manner.