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cilia are involved in diverse cellular functions, such as patterning of left-right asymmetry (nodal cilia), limb development, bone morphogenesis, and neurosensory functions (mechanosensation, olfaction, and photoreception). Cilia are also implicated in several developmental cascades, such as Wnt signaling, sonic hedgehog signaling, and platelet derived growth factor receptor signaling pathways. | Chapter 2 Photoreceptor Sensory Cilium and Associated Disorders Linjing Li Ozge Yildiz Manisha Anand and Hemant Khanna Additional information is available at the end of the chapter http dx.doi.org 10.5772 48387 1. Introduction The primary cilium is a microtubule-based extension of the plasma membrane which is present in almost all cell types. Ciliary microtubules extend from a basal body or mother centriole which docks at the apical membrane. Elegant studies have been carried out to determine the mechanism that regulates the docking of the mother centriole at the membrane for cilia formation. Cilia function as antennae of the cell to detect chemical and physical changes of the microenvironment 1-5 . Owing to their near-ubiquitous nature cilia are involved in diverse cellular functions such as patterning of left-right asymmetry nodal cilia limb development bone morphogenesis and neurosensory functions mechanosensation olfaction and photoreception . Cilia are also implicated in several developmental cascades such as Wnt signaling sonic hedgehog signaling and platelet derived growth factor receptor signaling pathways. Such functions of cilia are brought about by the ability of the ciliary membrane to concentrate a specific subset of membrane proteins in the ciliary compartment as compared to the rest of the cell membrane 6-8 . Cilia are generated by an elaborate process of formation of multiple protein complexes and molecular motor dependent transport of membrane cargo from the proximal to the distal tip thereby extending the microtubule-based axoneme and the ciliary membrane. Such transport called Intraflagellar Transport was initially identified in green alga Chlamydomonas reinhardtii and is composed of more than 20 IFT subunits arranged in two distinct complexes IFT-A and IFT-B 9-10 . They interact with motors and transport cargo along axoneme 11 . Microtubules are polarized with a plus end growing tip and a minus end at the proximal end of cilia . The anterograde