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A Shh/Gli-driven three-node timer motif controls temporal identity and fate of neural stem cells.

ABSTRACT: How time is measured by neural stem cells during temporal neurogenesis has remained unresolved. By combining experiments and computational modeling, we define a Shh/Gli-driven three-node timer underlying the sequential generation of motor neurons (MNs) and serotonergic neurons in the brainstem. The timer is founded on temporal decline of Gli-activator and Gli-repressor activities established through down-regulation of Gli transcription. The circuitry conforms an incoherent feed-forward loop, whereby Gli proteins not only promote expression of Phox2b and thereby MN-fate but also account for a delayed activation of a self-promoting transforming growth factor-? (Tgf?) node triggering a fate switch by repressing Phox2b. Hysteresis and spatial averaging by diffusion of Tgf? counteract noise and increase temporal accuracy at the population level, providing a functional rationale for the intrinsically programmed activation of extrinsic switch signals in temporal patterning. Our study defines how time is reliably encoded during the sequential specification of neurons.

SUBMITTER: Dias JM

PROVIDER: S-EPMC7494341 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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A Shh/Gli-driven three-node timer motif controls temporal identity and fate of neural stem cells.

Dias José M JM Alekseenko Zhanna Z Jeggari Ashwini A Boareto Marcelo M Vollmer Jannik J Kozhevnikova Mariya M Wang Hui H Matise Michael P MP Alexeyenko Andrey A Iber Dagmar D Ericson Johan J

Science advances 20200916 38

How time is measured by neural stem cells during temporal neurogenesis has remained unresolved. By combining experiments and computational modeling, we define a Shh/Gli-driven three-node timer underlying the sequential generation of motor neurons (MNs) and serotonergic neurons in the brainstem. The timer is founded on temporal decline of Gli-activator and Gli-repressor activities established through down-regulation of Gli transcription. The circuitry conforms an incoherent feed-forward loop, whe ...[more]

PMID: 32938678

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Project description:The increasing number of developmental events and molecular mechanisms associated with the Hedgehog (Hh) pathway from Drosophila to vertebrates, suggest that gene regulation is crucial for diverse cellular responses, including target genes not yet described. Although several high-throughput, genome-wide approaches have yielded information at the genomic, transcriptional and proteomic levels, the specificity of Gli binding sites related to direct target gene activation still remain elusive. This study aims to identify novel putative targets of Gli transcription factors through a protein-DNA binding assay using yeast, and validating a subset of targets both in-vitro and in-vivo. Testing in different Hh/Gli gain- and loss-of-function scenarios we here identified known (e.g., ptc1) and novel Hh-regulated genes in zebrafish embryos.The combined yeast-based screening and MEME/MAST analysis were able to predict Gli transcription factor binding sites, and position mapping of these sequences upstream or in the first intron of promoters served to identify new putative target genes of Gli regulation. These candidates were validated by qPCR in combination with either the pharmacological Hh/Gli antagonist cyc or the agonist pur in Hh-responsive C3H10T1/2 cells. We also used small-hairpin RNAs against Gli proteins to evaluate targets and confirm specific Gli regulation their expression. Taking advantage of mutants that have been identified affecting different components of the Hh/Gli signaling system in the zebrafish model, we further analyzed specific novel candidates. Studying Hh function with pharmacological inhibition or activation complemented these genetic loss-of-function approaches. We provide evidence that in zebrafish embryos, Hh signaling regulates sfrp2, neo1, and c-myc expression in-vivo.A recently described yeast-based screening allowed us to identify new Hh/Gli target genes, functionally important in different contexts of vertebrate embryonic development.

Project description:Sonic hedgehog (Shh) signaling is critical during development and its aberration is common across the spectrum of human malignancies. In the cerebellum, excessive activity of the Shh signaling pathway is associated with the devastating pediatric brain tumor medulloblastoma. We previously demonstrated that exaggerated de novo lipid synthesis is a hallmark of Shh-driven medulloblastoma and that hedgehog signaling inactivates the Rb/E2F tumor suppressor complex to promote lipogenesis. Indeed, such Shh-mediated metabolic reprogramming fuels tumor progression, in an E2F1- and FASN-dependent manner. Here, we show that the nutrient sensor PPAR? is a key component of the Shh metabolic network, particularly its regulation of glycolysis. Our data show that in primary cerebellar granule neural precursors (CGNPs), proposed medulloblastoma cells-of-origin, Shh stimulation elicits a marked induction of PPAR? alongside major glycolytic markers. This is also documented in the actively proliferating Shh-responsive CGNPs in the developing cerebellum, and PPAR? expression is strikingly elevated in Shh-driven medulloblastoma in vivo. Importantly, pharmacological blockade of PPAR? and/or Rb inactivation inhibits CGNP proliferation, drives medulloblastoma cell death and extends survival of medulloblastoma-bearing animals in vivo. This coupling of mitogenic Shh signaling to a major nutrient sensor and metabolic transcriptional regulator define a novel mechanism through which Shh signaling engages the nutrient sensing machinery in brain cancer, controls the cell cycle, and regulates the glycolytic index. This also reveals a dominant role of Shh in the etiology of glucose metabolism in medulloblastoma and underscores the function of the Shh ? E2F1 ? PPAR? axis in altering substrate utilization patterns in brain cancers in favor of tumor growth. These findings emphasize the value of PPAR? downstream of Shh as a global therapeutic target in hedgehog-dependent and/or Rb-inactivated tumors.

Dataset Information

A Shh/Gli-driven three-node timer motif controls temporal identity and fate of neural stem cells.

Publications

A Shh/Gli-driven three-node timer motif controls temporal identity and fate of neural stem cells.

Similar Datasets

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