Ciliary pore complex

The protocoatomer hypothesis suggest a common evolutionary origin for key eukaryotic complexes like nuclear pores complexes (NPC) and coated vesicles based on a typical domain architecture, the membrane coat (MC) architecture, found only in some of the proteins forming those complexes. Adding to a growing list of data, Kee et al. (2012) Nat. Cell Biol. 14, 431–7, see also the preview by Obado and Rout (2012) Developmental Cell 22, 693-4, suggest that this connection should be increased to include cilia, another key eukaryotic feature. The presence of karyopherins and of a Ran gradient in both systems (Dishinger et al., 2010) already provided some links between the NPC and the cilia. At least one karyopherin recognize a CLS (ciliary localization sequence) that is suspiciously similar to a NLS (nuclear localization sequence). In addition, MC proteins are also found inside the cilia in the transport complexes (Taschner et al., 2012) and components of the BBSome (a multi-protein complex involved in cilia transport) share related structural organization with the coat complexes (Jin et al., 2010). Because this protein architecture is also found in clathrin, COPI and COPII complexes, this suggests a common evolutionary origin to NPCs, coated vesicles and some ciliary components in, to cite the original protocoatomer hypothesis,

an early membrane-curving module that led to the formation of the internal membrane systems in modern eukaryotes,

which can now possibly be expanded to include the cilia or its ancestor.

The origin of the eukaryotic cell is becoming a more complex but also more fascinating issue.