Bunched specifically regulates alpha/beta mushroom body neuronal cell proliferation during metamorphosis

In Drosophila, mushroom bodies are centers for higher order behavior. Mushroom body neurons consist of three distinct types of neuronal cells, alpha, alpha'/beta', and alpha/beta, which are all generated by the same neuroblasts. The mechanism by which a single neuroblast generates three different types of mushroom body neurons is a compelling area of research. Here, we report that bunched (bun) is expressed only in alpha/beta-type mushroom body neurons and that mutation of the bun gene only affects the development of alpha/beta neurons. Reduced bun expression causes decreased and premature arrest of neuroblast cell division, which results in reduced numbers of alpha/beta neurons and thin axon bundled formation. We propose that bun acts as a specific factor in regulating neuroblast mitotic activity during the development of alpha/beta neurons.