Mef-2 and p300 interact to regulate expression of the homeostatic regulator Pumilio in Drosophila

Abstract (174 words)Pumilio (Pum) is a key component of neuron firing-rate homeostasis that maintains stability of neural circuit activity. Whilst Pum is ubiquitously expressed, we understand little about how synaptic excitation regulates its expression. Here, we characterised the Drosophila dpum promoter and identified multiple Myocyte enhancer factor-2 (Mef2)-binding elements. To understand the transactivation capability of dMef2, 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 CNS exposed to picrotoxin (PTX). The lack of activity-dependence is indicative of additional regulation. We identified p300 as a likely candidate. We show that by binding to dMef2, p300 represses dpum transactivation. Significantly, p300 transcript is down-regulated by enhanced synaptic excitation (PTX) which, in turn, increases transcription of dpum through derepression of dMef2. These results suggest the activity-dependent expression of dpum is regulated by an interaction between p300 and dMef2.