| The mammalian photoreceptor is an excellent model to study intracellular transport in general and ciliary transport (termed intraflagellar transport or IFT for its identification in flagellated organisms) in particular. Phototransduction proteins must be transported from biosynthetic inner segments to light-sensing outer segments. Photoreceptors contain a primary cilium which acts as the major thoroughfare between the inner and outer segment. Transport of ciliary cargo in this model and others remains an open question.;In Chapter 1, I review fundamentals of photoreceptor structure and function as well as properties shared by other primary cilia. The importance of various proteins in phototransduction, light adaptation and dark adaptation are discussed. Additionally, diseases previously attributed to defects in ciliary formation and transport are mentioned.;Chapter 2 focuses on photoreceptor-specific deletion of a subunit of the kinesin-II anterograde IFT motor, KIF3A. Kif3a has been deleted previously in rod photoreceptors and was thought to be important for transport of the light sensing pigment, rhodopsin. The role of kinesin-II in cones, however, has never been addressed. In this chapter, I show that kinesin-II is responsible for transport of membrane associated proteins in cones. Upon further analysis of Kif3a-deleted rods using a different CRE line than used previously, I found that kinesin-II is not in fact responsible for trafficking of rhodopsin. The discrepancies between the two findings are discussed.;In Chapter 3, I analyze a knock-in mouse I generated for deletion of the ciliary Cetn1 gene. The localization and in vitro interactions of centrin-1 suggest its role in light-dependent transport of the G protein transducin. Deletion of centrin-1 globally resulted in viable and fertile mice. In photoreceptors, transducin and other phototransduction proteins showed normal localization. By two months of age, retinas did not degenerate and photoreceptor function was preserved. Absence of differences between normal and mutant mice is attributed to compensation by the highly related centrin-2.;Chapter 4 includes a discussion of the implication of my results in the context of nonphotoreceptor cells as well as future directions that might elucidate further the role of these critical ciliary proteins in IFT. |
