We show in this study that brain and intestinal stem cells of Drosophila contain a new type of cytoplasmic protrusion which is enriched in mitochondria and that the mitochondria are probably dependent on microtubules for their distribution. The protrusions form mitochondria-enriched cytoplasmic bridges from the stem cells to their niche that we speculate are important in regulating stem cell quiescence and activation.
Specimen preparation: Larval brains (LBs) were prepared from starved (amino acid-restricted) first instar (L1) larvae to enrich for quiescent neural stem cells. The LBs were glutaraldehyde-fixed, tannic acid and OsO4-stained, embedded in resin, thin-sectioned (60-70 nm) and stained with uranyl acetate/lead citrate, then observed by TEM.