JAK/STAT pathway promotes Drosophila neuroblast proliferation via the direct CycE regulation

How neural stem cells regulate their proliferative potential and lineage diversity is a central problem in developmental neurobiology. Drosophila Mushroom bodies (MBs), centers of olfactory learning and memory, are generated by a specific set of neuroblasts (Nbs) that are born in the embryonic stage and continuously proliferate till the end of the pupal stage. Although MB presents an excellent model for studying neural stem cell proliferation, the genetic and molecular mechanisms that control the unique proliferative characteristics of the MB Nbs are largely unknown. Further, the signaling cues controlling cell cycle regulators to promote cell cycle progression in MB Nbs remain poorly understood. Here, we report that JAK/STAT signaling pathway is required for the proliferation activity and maintenance of MB Nbs. Loss of JAK/STAT activity severely reduces the later-born MB neuron types and leads to premature neuroblast termination, which can be rescued by tissue-specific overexpression of CycE and diap1. Higher JAK/STAT pathway activity in MB results in more neurons, without producing supernumerary Nbs. Furthermore, we show that JAK/STAT signaling effector Stat92E directly regulates CycE transcription in MB Nbs. Finally, MB Nb clones of loss or excess CycE phenocopy those of decreased or increased JAK/STAT signaling pathway activities. We conclude that JAK/STAT signaling controls MB Nb proliferative activity through directly regulating CycE expression to control cell cycle progression.