Different regions of Klarsicht are required for nuclear migration and lipid-droplet motion. Y. Guo , M. Welte. Brandeis University, Waltham, MA.

   The Klar protein is necessary for organelle movement during two times in development: the migration of photoreceptor nuclei in eye imaginal disks and the motion of lipid droplets in early embryos. In both cases, Klar is necessary for a developmentally regulated switch from net basal to net apical motion. The sequence of Klar is novel and has not provided any insight into how it functions mechanistically. We present evidence that Klar plays distinct roles in these two transport processes. On the one hand, we have identified several klar alleles that have differential effects on the transport of lipid droplets and photoreceptor nuclei. Lesions that remove the very 3' end of the klar gene interfere with eye development, but still support normal net transport of lipid droplets. This observation suggests that the C-terminal domain of Klar is specifically required for its role in nuclear migration but dispensable for droplet motion. On the other hand, the expression pattern of Klar differs in the two tissues. In the eye disk, the switch in the directionality of transport correlates with de novo expression of klar mRNA. Here we report the expression of Klar during embryogenesis. Western analysis reveals the presence of a set of more than 7 different Klar polypeptides in early embryos; these proteins vary greatly in size (50- 280 kDa), and their expression levels are characteristically altered in various klar mutants. These isoforms are present before, during, and after the switch in droplet transport, suggesting that in the embryo reversal in transport direction is not simply initiated by new expression of Klar. We will present how the expression profile of these isoforms changes developmentally and how it is affected by various klar mutations.