Brain tumor restricts developmental potential in intermediate progenitor cells

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DESCRIPTION (provided by applicant): Intermediate progenitor cells possess restricted developmental potential allowing them to amplify the output of stem cells, but how their potential is established remains unknown. In the Drosophila larval brain, the TRIM-NHL protein Brain tumor (Brat) is required for formation of intermediate neural progenitors (INPs), but the mechanisms are controversial. Here, we show that Brat establishes restricted potential in the immature INP by inducing differentiation and suppressing de-differentiation via the evolutionarily conserved B-boxes. Brat induces differentiation by promoting nuclear localization of the transcriptional activator PointedP1 in the immature INP, where PointedP1 triggers timely differentiation via a novel receptor tyrosine kinase-independent mechanism. Furthermore, Brat suppresses de-differentiation of the immature INP by maintaining expression of the Adenomatous polyposis coli 2 protein and antagonizing the function of the ¿-catenin independently of the receptor Frizzled. Thus, Brat promotes generation of post-mitotic progeny and prevents accumulation of aberrant progenitors by restricting the developmental potential in the INP. Giving all TRIM family proteins contain at least one B-box, the mechanism by which Brat restricts the developmental potential in the INP might be relevant to other stem cell lineages, and will likely provide novel mechanistic insight into tumors arisen from de-regulation of intermediate progenitor cells.