Proliferation pattern of postembryonic neuroblasts in the brain of Drosophila melanogaster

Abstract

The spatio-temporal proliferation pattern of postembryonic neuroblasts in the central brain region of the supraesophageal ganglion of Drosophila melanogaster was studied by labeling DNA replicating cells with 5-bromo-2′-deoxyuridine (BrdU). There are five proliferating neuroblasts per hemisphere in larvae just after hatching: one in the ventro-lateral, and the other four in the postero-dorsal region of the brain. Dividing neuroblasts increase during the late first-late second instar larval stages, reaching a plateau of about 85 neuroblasts per hemisphere. Most neuroblasts cease dividing 20–30 hr after puparium formation (APF), while only four in the postero-dorsal region continue making progenies until 85–90 hr APF. The four distinct neuroblasts proliferating in the early larval and late pupal stages are identical; they lie in the cortex above the calyces of the mushroom bodies (corpora pedunculata), proliferating over a period twice as long as that for the other neuroblasts. Their daughter neurons project into the mushroom body neuropile, and hence are likely to be the Kenyon cells. The cell-cycle period of the four neuroblasts (named mushroom body neuroblasts: MBNbs) is rather constant (1.1–1.5 hr) during the mid larval-early pupal stages and is longer before and after that. The total number of the MBNb progenies made throughout the embryonic and postembryonic development was estimated to be 800–1200 per hemisphere.