Short Stop is a Gatekeeper at the Ring Canals of <i>Drosophila</i> Ovary

Abstract

Microtubules and actin filaments are two major cytoskeletal components essential for a variety of cellular functions. Spectraplakins are a family of large cytoskeletal proteins cross-linking microtubules and actin filaments among other components. In this study, we aim to understand how Short stop (Shot), the single Drosophila spectraplakin, coordinates microtubules and actin filaments for oocyte growth. The oocyte growth completely relies on the acquisition of cytoplasmic materials from the interconnected sister cells (nurse cells), through ring canals, cytoplasmic bridges that remained open after incomplete germ cell division. Given the open nature of the ring canals, it is unclear how the direction of transport through the ring canal is controlled. Here we show that Shot controls the directionality of flow of material from the nurse cells towards the oocyte. Knockdown of shot changes the direction of transport of many types of cargo through the ring canals from unidirectional (toward the oocyte) to bidirectional, resulting in small oocytes that fail to grow over time. In agreement with this flow-directing function of Shot, we find that it is localized at the asymmetric actin fibers adjacent to the ring canals at the nurse cell side, and controls the uniform polarity of microtubules located in the ring canals connecting the nurse cells and the oocyte. Together, we propose that Shot functions as a gatekeeper directing the material flow from the nurse cells to the oocyte, via organization of microtubule tracks.