ABSTRACT
The number of neural stem cells reflects the total number of neurons in the mature brain. As neural stem cells arise from neuroepithelial cells, the neuroepithelial cell population must be expanded to secure a sufficient number of neural stem cells. However, molecular mechanisms that regulate timely differentiation from neuroepithelial to neural stem cells are largely unclear. Here, we show that TCF4/Daughterless is a key factor that determines the timing of the differentiation in Drosophila. The neuroepithelial cells initiated but never completed the differentiation in the absence of TCF4/Daughterless. We also found that TCF4/Daughterless binds to the Notch locus, suggesting that Notch is one of its downstream candidate genes. Consistently, Notch expression was ectopically induced in the absence of TCF4/Daughterless. Furthermore, ectopic activation of Notch signaling phenocopied loss of TCF4/Daughterless. Our findings demonstrate that TCF4/Daughterless directly inactivates Notch signaling pathway, resulting in completion of the differentiation from neuroepithelial cells into neural stem cells with optimal timing. Thus, the present results suggest that TCF4/Daughterless is essential for determining whether to move to the next state or stay in the current state in differentiating neuroepithelial cells.
Footnotes
Author contributions
Conceptualization: A.T., T.S.; Validation: C.A., Y.T., T.S.; Formal analysis: T.S.; Investigation: C.A., A.T., Y.T., M.H., T.S.; Writing - original draft: A.T., T.S.; Visualization: C.A., Y.T., M.H.; Supervision: T.S.; Project administration: A.T., T.S.; Funding acquisition: Y.T., T.S.
Funding
This work was supported by a Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research (C) (JP21K06196 and JP24K09465 to T.S.) and Grant-in-Aid for Research Activity Start-up (JP19K23739 to T.S.), by a Japan-Taiwan Exchange Association scholarship (33063 to Y.T.), by a Research Booster Program from Ibaraki University (2019 and 2022 to T.S.), by the Inamori Foundation, by the Mochida Memorial Foundation, by the Ichiro Kanehara Foundation, by the Uehara Memorial Foundation, by the Nakajima Foundation, by the Naito Foundation, by the Terumo Life Science Foundation, by the Sumitomo Foundation, the Life Science Foundation of Japan, by the Novartis Foundation (Japan) for the Promotion of Science, by a Narishige Zoological Science Award, by the Chugai Foundation for Innovative Drug Discovery Science, by the Asahi Glass Foundation, by the Takeda Science Foundation, by The Kato Memorial Bioscience Foundation, by the Suzuken Memorial Foundation, by the Takahashi Industrial and Economic Research Foundation, by The Hitachi Global Foundation, by the Astellas Foundation for Research on Metabolic Disorders and by The Sumitomo Electric Group CSR Foundation (to T.S.).
Data availability
Raw sequencing data of all datasets in this study have been deposited in the NCBI Sequence Read Archive under accession number PRJNA1131592.
