Novel Isoforms of the Transport Regulator Klar

Klar is a regulator of microtubule-motor dependent transport processes in Drosophila, including nuclear migration, vesicle motility, and lipid-droplet transport. The single klar locus gives rise to multiple isoforms that presumably have unique functions. Up to now, three Klar isoforms (α, β, γ) were known. Here we describe two novel isoforms, δ and ε, whose expression depends on a previously uncharacterized promoter. Klar δ and/or ε are widely expressed during development, including in the embryonic and larval nervous system as well as in ovaries. When we specifically ablate Klar δ and ε expression genetically, no gross organismal phenotypes are apparent. However, ectopic expression of these isoforms causes nuclear mispositioning in developing photoreceptors and in oocytes, demonstrating their biological activity. Our analysis identifies novel forms of the Klar protein and provides new tools for functionally dissecting the complex klar locus.