The male stem cell niche of Drosophila melanogaster: Interactions between the germline stem cells and the hub

Highlights: • The male germ stem cells of Drosophila display an apical smooth profile or distinct membrane protrusions. • Surface protrusion of the stem cells interdigitate with opposite protrusions from the hub cells. • Some protrusions of the stem cells are very elongated and extend into the hub. • The adherens junctions between the stem cells and the hub have an asymmetric organization. -- Abstract: The Drosophila male stem cell niche is a well characterized structure in which a small cluster of somatic cells send self-renewal signals to neighbouring germ cells. Although the molecular information involved in the stem cell fate have been identified, much less is understand on the mechanisms driving their short-range specific release. Our ultrastructural analysis reveals distinct protrusions of the stem cell plasma membrane that interdigitate with membrane protrusions of the facing hub cells. Some of these protrusions are very elongated and extend into the hub and could correspond to the Mt-Nanotubes. Therefore, the interface between the stem cells and the hub appears more complex than previously reported and the membrane protrusions of the stem cells might represent specialized surface areas involved in the niche-stem cell communication. We also noticed the presence of clathrin-coated vesicles in the germline plasma membrane that might be also involved in delivering information from the hub.