Myocyte enhancer factor-2 and p300 interact to regulate expression of the homeostatic regulator Pumilio in Drosophila.

Pumilio (Pum), an RNA-binding protein, is a key component of neuron firing-rate homeostasis that likely maintains stability of neural circuit activity in all animals, from flies to mammals. Whilst Pum is ubiquitously expressed, we understand little about how synaptic excitation regulates its expression in the CNS. Here, we characterized the Drosophila dpum promoter and identified multiple Myocyte enhancer factor-2 (Mef2)-binding elements. We cloned 12 dmef2 splice variants and used a luciferase-based assay to monitor dpum promoter activity. Whilst all 12 dMef2 splice variants enhance dpum promoter activity, exon 10-containing variants induce greater transactivation. Previous work shows dPum expression increases with synaptic excitation. However, we observe no change in dmef2 transcript in larval CNS, of both sexes, exposed to the proconvulsant picrotoxin. The lack of activity-dependence is indicative of additional regulation. We identified p300 as a potential candidate. We show that by binding to dMef2, p300 represses dpum transactivation. Significantly, p300 transcript is down-regulated by enhanced synaptic excitation (picrotoxin) which, in turn, increases transcription of dpum through de-repression of dMef2. These results advance our understanding of dpum by showing activity-dependent expression is regulated by an interaction between p300 and dMef2. This article is protected by copyright. All rights reserved.