Active EB1 surges promote tubulin influx into the growing outer segments of the bipartite olfactory cilia in Drosophila

Abstract: Like a photoreceptor cilium, the sensory cilia have a complex bipartite architecture containing 9+0 connecting cilium at the base and a singlet microtubule-supported, highly membranous outer segment, essential for the receptor display. How such diverse cilia morphology and underlying microtubule cytoskeleton develops remains unclear. Here we show that individual olfactory cilium, inside the large basiconic sensilla in developing Drosophila antenna, grows in episodic steps following several pulsatile influxes of tubulin. Each tubulin influx event is preceded by transient elevations of a microtubule-stabilising protein, the End-binding protein 1 (EB1). Additionally, EB1 is found to specifically interact with the tail domain of Drosophila KLP68D, an orthologue of the kinesin-2beta motor subunit, in vitro. Finally, the loss of EB1 in olfactory neurons preceding the growth surges reduces the tubulin influx as well as arrests the olfactory cilia assembly and stability. These findings suggest a novel mechanism of bipartite cilia assembly.