In contrast to the radial microtubule arrays organized by centrosomes in dividing cells, many differentiated cells assemble non-centrosomal microtubule arrays adapted for specific cellular functions, including nuclear positioning and migration, maintenance of tissue architecture and intracellular transportation. In an RNAi screen in C. elegans, we identified NOCA-1 as a novel protein that does not contribute to centrosome-driven embryonic cell divisions but is required to form microtubule arrays in the germline that are essential for organismal fertility. In this dissertation, I focused on NOCA-1 to study the assembly mechanism and cellular function of non- centrosomal microtubule arrays. The noca-1 gene encodes 8 isoforms expressed in a variety of tissues. Two distinct long isoforms control assembly of microtubule arrays in the germline and embryonic epidermis, respectively. In contrast, a short isoform functions in parallel to the microtubule minus end-binding protein Patronin (PTRN-1) to control assembly of microtubule arrays in the post- embryonic epidermis. Evidence for the redundant activity of NOCA-1 and PTRN-1 includes synthetic lethality and early larval stage dye permeability of noca-1[Delta];ptrn- 1[Delta] double mutants, both of which are rescued by selectively expressing PTRN-1 in the post-embryonic epidermis. In support of the genetic interaction, NOCA-1 co-sediments with taxol-stabilized microtubules from worm lysates and purified recombinant NOCA-1, like PTRN-1, binds to microtubule ends in a microtubule-anchoring assay. We conclude that NOCA-1 represents a new class of microtubule end-binding proteins with essential functions of its own, as well as parallel functions with Patronin, in the assembly of non-centrosomal microtubule arrays in multiple C. elegans tissues. Non-centrosomal microtubule arrays in embryonic epidermis contribute to elongation, the process that converts the oval-shaped embryo into an elongated worm. By using two different means of disrupting microtubules, we showed that disrupting microtubules alone does not affect elongation. However, when acto-myosin contractility is compromised by a partial loss-of-function mutant of let-502 (a Rho kinase), disrupting microtubules results in elongation arrests and causes embryonic lethality. Intact microtubules and normal LET-502 activity are required for E-cadherin clustering at adherens junctions and the maturation of hemidesmosomes, possibly explaining the elongation defects we observed. We conclude that microtubules in the embryonic epidermis contribute to elongation, but only is required when actomyosin contractility is reduce
