Sensory cilia and integration of signal transduction in human health and disease

The primary cilium is a hallmark of mammalian tissue cells. Recent research has shown that these organelles display unique sets of selected signal transduction modules including receptors, ion channels, effector proteins and transcription factors that relay chemical and physical stimuli from the extracellular environment in order to control basic cellular processes during embryonic and postnatal development, as well as in tissue homeostasis in adulthood. Consequently, defects in building of the cilium or in transport or function of ciliary signal proteins are associated with a series of pathologies, including developmental disorders and cancer. In this review, we highlight recent examples of the mechanisms by which signal components are selectively targeted and transported to the ciliary membrane and we present an overview of the signal transduction pathways associated with primary and motile cilia in vertebrate cells, including platelet-derived growth factor receptor-alpha (PDGFR alpha), hedgehog and Wnt signaling pathways. Finally, we discuss the functions of these cilia-associated signal transduction pathways and their role in human health and development.