Steroid hormone induction of temporal gene expression in Drosophila brain neuroblasts generates neuronal and glial diversity

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Abstract

An important question in neuroscience is how stem cells generate neuronal diversity. During Drosophila embryonic development, neural stem cells (neuroblasts) sequentially express transcription factors that generate neuronal diversity; regulation of the embryonic temporal transcription factor cascade is lineage-intrinsic. In contrast, larval neuroblasts generate longer ~50 division lineages, and currently only one mid-larval molecular transition is known: Chinmo/Imp/Lin-28+ neuroblasts transition to Syncrip+ neuroblasts. Here we show that the hormone ecdysone is required to down-regulate Chinmo/Imp and activate Syncrip, plus two late neuroblast factors, Broad and E93. We show that Seven-up triggers Chinmo/Imp to Syncrip/Broad/E93 transition by inducing expression of the Ecdysone receptor in mid-larval neuroblasts, rendering them competent to respond to the systemic hormone ecdysone. Importantly, late temporal gene expression is essential for proper neuronal and glial cell type specification. This is the first example of hormonal regulation of temporal factor expression in Drosophila embryonic or larval neural progenitors.

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Mubarak Hussain Syed

Institute of Neuroscience, Howard Hughes Medical Institute, University of Oregon, Eugene, United States

Competing interests
The authors declare that no competing interests exist.
Brandon Mark

Institute of Neuroscience, Howard Hughes Medical Institute, University of Oregon, Eugene, United States

Competing interests
The authors declare that no competing interests exist.
Chris Q Doe

Institute of Neuroscience, Howard Hughes Medical Institute, University of Oregon, Eugene, United States

For correspondence
cdoe@uoregon.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-5980-8029

Funding

Howard Hughes Medical Institute (n/a)

Brandon Mark

National Institutes of Health (HD27056)

Brandon Mark

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.