Literature Review of IFT Mechanisms and Functions in the Immune Synapse and Protein Family Tektin

Abstract

Cilia are microtubule based organelles that serve as specialized projections for the cell. There are two distinct forms of cilia—motile and non-motile. Motile cilia have responsibilities in cell locomotion and patterned beating, as well as the movement of fluid over cell surfaces. Non-motile or primary cilia, function in sensory perception for the cell often sensing extracellular signals and transmits signals from the cilium to the cytoplasm in order to control gene expression and cell behavior. Cilia are comprised of many proteins, but a main focus of this thesis are tektin proteins. Tektin is a family of proteins that provide structural support and are closely related to intermediate filaments and nuclear lamins. In order for both variations of cilia to develop, a system known as intraflagellar transport (IFT) must be functional. IFT is a motor-dependent cargo transport that is crucial for ciliary elongation, maintenance, and assembly of cilia. IFT is a coupled-bidirectional system that is comprised of two subcomplexes—IFT-A complex and IFT-B complex. The IFT-A complex primarily acts within retrograde transport to maintain the inward movement of materials, where as the IFT-B complex is involved with anterograde transport or outward movement of material during elongation and maintenance of cilia. Surprisingly, IFT has been found in cells that lack the presence of cilia. This can be seen in the formation of immune synapses of cytotoxic T-cells, which occurs at the same site where a primary cilium would develop. Although cytotoxic T-cells have not shown any projected appendages, there is a small bump present in the membrane that closely resembles the beginning formations of a primary cilium. This has been classified as a “frustrated cilium”, where IFT proteins have been isolated and studied. This thesis reviews some of the recent literature on the tektin protein family and the functions of IFT proteins in both cilia and the immune synapse.