Collaborative repressive action of the antagonistic ETS transcription factors Pointed and Yan fine-tunes gene expression to confer robustness inDrosophila

Abstract

The acquisition of cellular identity during development depends on precise spatiotemporal regulation of gene expression, with combinatorial interactions between transcription factors, accessory proteins and the basal transcription machinery together translating complex signaling inputs into appropriate gene expression outputs. The opposing repressive and activating inputs of the ETS family transcription factors Yan and Pointed orchestrate numerous cell fate transitions downstream of receptor tyrosine kinase signaling, providing one of the premier systems for studying this process. Current models describe the differentiative transition as a switch from Yan-mediated repression to Pointed-mediated activation of common target genes. We describe here a new layer of regulation whereby Yan and Pointed co-occupy regulatory elements to repress gene expression in a coordinated manner, with Pointed being unexpectedly required for the genome-wide occupancy of both Yan and the co-repressor Groucho. Using as a test-case, synergistic genetic interactions between Pointed, Groucho, Yan and components of the RNA polymerase II pausing machinery suggest that Pointed integrates multiple scales of repressive regulation to confer robustness. We speculate that this mechanism may be used broadly to fine-tune the expression of many genes crucial for development.

Distinct roles and requirements forRaspathway signaling in visceral versus somatic muscle founder specification

“…Although our data argue against an absolute requirement for either Pnt or Aop, we cannot rule out a more limited contribution from these factors. Indeed, chromatin IP experiments indicate that Pnt can bind to the mib2 enhancer region, although it is not known in what cell types (Webber et al, 2018), and aop mutants show an effect on mib2 expression in the ventral midline (Fig. 4P).…”

“…In the absence of induction these sites are bound by the ETS-domain repressor Aop (also known as Yan) (Halfon et al, 2000, Webber et al, 2013, Boisclair Lachance et al, 2018). Recent evidence suggests that Pnt bound at these or other sites may also contribute to repression in the absence of MAPK activation (Webber et al, 2018). Importantly, experiments have shown that induction trumps repression: in the absence of both Pnt and Aop binding, there is no gene activation (Halfon et al, 2000 and unpublished data).…”

Lessons from Drosophila Pointed, an ETS family transcription factor and key nuclear effector of the RTK signaling pathway

“…The occupancy profiles of Pnt and Yan were found to be strikingly similar and moreover they were found to simultaneously occupy the enhancer regions of a subset of genes (Webber et al, ). Further examination revealed that Yan occupancy was surprisingly dependent on Pnt, as there was a global reduction of Yan occupancy in pnt mutant embryos compared with the wild‐type embryos (Webber et al, ). This unexpected result suggests that Pnt might be required to recruit Yan to repress the expression of a number of target genes.…”

“…However, while mutually exclusive expression was observed in certain tissues, Pnt and Yan co‐expression was also observed in different tissues throughout development (Boisclair Lachance et al, ). To explore the functional consequence of this overlap in Yan and Pnt expression, genome wide chromatin immunoprecipitation‐sequencing (ChIP‐seq) experiments were performed to determine Yan and Pnt occupancy profiles (Webber, Zhang, Cote, et al, ; Webber, Zhang, Massey, Sanchez‐Luege, & Rebay, ). The occupancy profiles of Pnt and Yan were found to be strikingly similar and moreover they were found to simultaneously occupy the enhancer regions of a subset of genes (Webber et al, ).…”

“…To explore the functional consequence of this overlap in Yan and Pnt expression, genome wide chromatin immunoprecipitation-sequencing (ChIP-seq) experiments were performed to determine Yan and Pnt occupancy profiles (Webber, Zhang, Cote, et al, 2013a;Webber, Zhang, Massey, Sanchez-Luege, & Rebay, 2018). The occupancy profiles of Pnt and Yan were found to be strikingly similar and moreover they were found to simultaneously occupy the enhancer regions of a subset of genes (Webber et al, 2018). Further examination revealed that Yan occupancy was surprisingly dependent on Pnt, as there was a global reduction of Yan occupancy in pnt mutant embryos compared with the wild-type embryos (Webber et al, 2018).…”