Investigating the interaction between the nuclear envelope protein KASH5 and dynein

Cytoplasmic dynein is a minus end directed microtubule motor protein. It is a multi-subunit complex that has many functions in eukaryotic cells, ranging from the transport of membrane cargoes during interphase to essential roles in spindle function during mitosis. Recently, dynein has been shown to participate in a critical process during meiosis, by driving telomere-led chromosome movements that are a prelude to chromosome pairing and recombination. Dynein interacts with the LINC complex component and outer nuclear membrane (ONM) protein, KASH5. The inner nuclear membrane (INM) partner of KASH5, SUN1, associates with the telomeres of meiotic chromosomes, providing a connection between the meiotic nucleus and cytoskeleton. By manipulating the subunit composition and activity of dynein, dynactin and associated proteins, the means by which KASH5 recruits dynein is becoming clearer. Dynein interacts directly with KASH5 via LICs 1 and 2, which function redundantly in recruitment of KASH5 to dynein. In contrast to the generally accepted dogma, dynactin, the major dynein accessory protein, is not required for recruitment of dynein to KASH5 and is instead recruited downstream of dynein. The accessory protein LIS1 may play a role in regulating the interaction between KASH5 and dynactin but is not required for dynein recruitment. The data presented in this thesis suggests that KASH5 could be a new member of the adaptor protein family that assembles with dynein and dynactin in tripartite complexes. Further work has addressed the functional significance of a KASH5 mutation that causes infertility in human patients. This mutation caused KASH5 to relocalise from the NE/ER membrane network to the mitochondria in cultured cells. Such mislocalisation in sperm would be predicted to prevent chromosome movement in prophase I, leading to meiotic failure and infertility.