Retinal ciliopathies through the lens of Bardet-Biedl Syndrome: Past, present and future

Motile and non-motile primary cilia are nearly ubiquitous cellular organelles. Dysfunction of cilia is being found to cause increasing numbers of diseases that are known as ciliopathies. The characterization of ciliopathy-associated proteins and phenotypes is increasing our understanding of how cilia are formed and compartmentalized and how they function to maintain human health.

Cilia are complex structures that have garnered interest because of their roles in vertebrate development and their involvement in human genetic disorders. In contrast to multicellular invertebrates in which cilia are restricted to specific cell types, these organelles are found almost ubiquitously in vertebrate cells, where they serve a diverse set of signaling functions. Here, we highlight properties of vertebrate cilia, with particular emphasis on their relationship with other subcellular structures, and explore the physiological consequences of ciliary dysfunction.

The primary cilium has recently stepped into the spotlight, as a flood of data show that this organelle has crucial roles in vertebrate development and human genetic diseases. Cilia are required for the response to developmental signals, and evidence is accumulating that the primary cilium is specialized for hedgehog signal transduction. The formation of cilia, in turn, is regulated by other signalling pathways, possibly including the planar cell polarity pathway. The cilium therefore represents a nexus for signalling pathways during development. The connections between cilia and developmental signalling have begun to clarify the basis of human diseases associated with ciliary dysfunction.