Polar cell membrane nanotubes containing microtubules and acidic vesicles render Drosophila eggs fertile.

Membrane nanotubes serve as critical cytoskeletal structures that facilitate intercellular communication and signal transmission across distances in both plants and animals. Here, we report the role of microtubule (MT) nanotubes in rendering the Drosophila micropyle functional, a structure essential for sperm entry during fertilization. Our study highlights that MT-nanotubes emanate from the apical end of the specialized epithelial cells called the polar cells in late oogenesis, forming a narrow channel through the eggshell. Utilizing a combination of fly genetics, live cell imaging, and tissue immunochemistry, our research elucidates the structural and functional characteristics of the polar cell nanotube. We show that tubulin is vital for the formation of these nanotubes, which are enriched in the lateral membrane marker, Fasciclin III. Moreover, the overall polarity of the migrating border cell cluster is critical for the successful development of the micropyle. Notably, both lysosomal function and lysosomal trafficking within the polar cells are essential for the opening of the vitelline layer, further facilitating the micropyle's role in fertilization.