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Control of neural daughter cell proliferation by multi-level Notch/Su(H)/E(spl)HLH signaling. (PMID: 27070787)

ABSTRACT: We expressed DamID and Flag-tagged versions of E(spl)HLH-m5, -m8 and Su(H), in Drosophila embryos and analyzed their DNA-binding by DamID-seq and ChIP-seq. The Notch pathway controls proliferation during development and in adulthood, and is frequently affected in many disorders. However, the genetic sensitivity and multi-layered transcriptional properties of the Notch pathway has made its molecular decoding challenging. Here, we address the complexity of Notch signaling with respect to proliferation, using the developing Drosophila CNS as model. We find that a Notch/Su(H)/E(spl)-HLH cascade specifically controls daughter, but not progenitor proliferation. Additionally, we find that different E(spl)-HLH genes are required in different neuroblast lineages. The Notch/Su(H)/E(spl)-HLH cascade alters daughter proliferation by regulating four key cell cycle factors: Cyclin E, String/Cdc25, E2f and Dacapo (mammalian p21CIP1/p27KIP1/p57Kip2). ChIP and DamID analysis of Su(H) and E(spl)-HLH indicates direct transcriptional regulation of the cell cycle genes, and of the Notch pathway itself. These results point to a multi-level signaling model, and may help shed light on the dichotomous proliferative role of Notch signaling in many other systems.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE137195 | GEO | 2019/09/11

REPOSITORIES: GEO

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Project description:Cellular responses to signalling pathways are often highly dynamic, however most analyses of developmental signalling pathways focus on a single endpoint. We have analyzed the temporal changes in transcription following a short Notch activation treatment and related these to the recruitment of the Notch pathway transcription factor, CSL [Suppressor of Hairless, Su(H), in Drosophila], and to the state of RNA Polymerase II (Pol II) binding. A total of 154 genes showed significant differential expression over time and their expression profiles stratified into 14 clusters based on temporal and quantitative differences in their responses. These differences were partially reflected in the profiles of Pol II and Su(H) binding. However, neither could fully account for the different response profiles. Furthermore, the timing of the different responses was unaffected by more prolonged Notch activation. Instead our data suggest that regulatory relationships between genes that segregate into different response clusters can partially account for the stratification. Thus, feed-forward repression, where products of early responding Enhancer of split bHLH genes (E(spl)bHLH) inhibit expression of endogenous repressors, is one mechanism that explains the profile of genes that exhibit delayed up-regulation. E(spl)bHLH genes may therefore be responsible for co-ordinating the Notch response of a wide spectrum of other targets, explaining their critical functions in many developmental and disease contexts. DmD8 cells were collected at 7 time points (0M-bM-^@M-^Y, 10M-bM-^@M-^Y, 20M-bM-^@M-^Y, 30M-bM-^@M-^Y, 40M-bM-^@M-^Y, 60M-bM-^@M-^Y and 100M-bM-^@M-^Y) after a 5 minute Notch stimulation as 3 independent replicates. Immunoprecipitation was performed with Su(H) antibody and compared to the total input DNA. Samples from replicates #1 and #2 were labelled with Cy5, and replicate #3 was labelled with Cy3 as a dye-swap. For time point 10M-bM-^@M-^Y, only 2 biological replicates were obtained.