Playing Well with Others: Extrinsic Cues Regulate Neural Progenitor Temporal Identity to Generate Neuronal Diversity

• Published in: Trends in genetics 2017-12, Vol.33 (12), p.933-942
• Main Authors: Syed, Mubarak Hussain, Mark, Brandon, Doe, Chris Q.
• Format: Article
• Language: English
• Subjects: Animals; Drosophila - genetics; Drosophila Proteins - genetics; Neural Stem Cells - physiology; Neurogenesis - physiology; Neurons - physiology; Stem Cells - physiology
• ISSN: 0168-9525
• DOI: 10.1016/j.tig.2017.08.005

During neurogenesis, vertebrate and Drosophila progenitors change over time as they generate a diverse population of neurons and glia. Vertebrate neural progenitors have long been known to use both progenitor-intrinsic and progenitor-extrinsic cues to regulate temporal patterning. In contrast, virtually all temporal patterning mechanisms discovered in Drosophila neural progenitors (neuroblasts) involve progenitor-intrinsic temporal transcription factor cascades. Recent results, however, have revealed several extrinsic pathways that regulate Drosophila neuroblast temporal patterning: nutritional cues regulate the timing of neuroblast proliferation/quiescence and a steroid hormone cue that is required for temporal transcription factor expression. Here, we discuss newly discovered extrinsic cues regulating neural progenitor temporal identity in Drosophila, highlight conserved mechanisms, and raise open questions for the future. Temporal patterning in both vertebrates and Drosophila is regulated by extrinsic cues. In mammals, TGFβ signaling regulates temporal patterning of neural progenitors in the midbrain and hindbrain. In mammals, Wnt7 from early-born deep layer neurons induces cortical neural progenitors to switch to late-born superficial layer neuron production. In Drosophila, nutrition (amino acids) initiate a signaling cascade leading to glial secretion of insulin-like peptides that induce timely neural stem cell exit from quiescence. In Drosophila, the steroid hormone ecdysone is required to trigger a switch from larval neuroblast production of early-born Chinmo+ Imp+ progeny to late-born Broad+ Syp+ progeny. Ecdysone may synchronize the generation of neural diversity with non-neuronal tissue development.