Stem cell niches are critical for providing resident stem cells with signals that specify their identity, and their signals only act over short distances so that they reach the progenitor cells only, not their differentiated progeny. However, the molecular mechanisms of this niche signalling were poorly understood. This recent study used Drosphila male germ line stem cells (from their testes) to identify and characterize microtubule (MT) -based nanotubes that extend from these cells into the hub, the central region of the niche. It also reported a finding that MT-nanotubes were specific only to germline stem cells. The hub secretes at least two ligands, one being a bone morphogenetic protein (BMP) ligand called Decapentaplegic (Dpp), which regulates the maintenance of germline stem cells.
Research has found that the interaction between these secreted Dpps, and BMP receptors called Thickveins (Thv), which are expressed in germ cells, is necessary for the formation of these MT-nanotubes. Also, the disruption of MT-nanotubes jeopardizes the Dpp signalling within germline stem cells, leading to the germline stem cell loss. Possible reasons why such a structure was not discovered before include the fact that they are sensitive to fixation, not always associated with the centrosome, and lacking acetylated microtubules. In sum, the ligand-receptor interaction (Dpp-Thv, respectively) promote MT-nanotube growth, which further enhances the signalling within stem cells in a niche, and leads spatially oriented self-renewal.
Article summary courtesy of Sean Ihn Reference: Nanotubes mediate niche-stem-cell signalling in the Drosophila testis, Mayu Inaba et al., Nature, doi:10.1038/nature14602, 1 July 2015