Cross-regulation of PHOX2A and PHOX2B transcription factors in the development of the Autonomic Nervous System

PHOX2A and PHOX2B are homeodomain transcription factors important for the development of the entire Autonomic Nervous System (sympathetic, parasympathetic and enteric divisions). PHOX2B is absolutely required at the early stages of development of autonomic ganglia: its expression is triggered by bone morphogenic proteins (BMPs) secreted by the dorsal aorta; it acts as a repressor of negative signals induced by Notch, a BMPs antagonist, and supports MASH1 with which it coordinates the expression of downstream factors as PHOX2A and dHAND, a process necessary to regulate the expression of c-RET, TH (tymidine hydroxylase) and DBH (dopamine β hydroxylase) genes which are characteristic to the cathecolaminergic phenotype. During the specification of neuronal identity, control of temporal and spatial expression of PHOX2A and PHOX2B is fundamental, and many studies over the last few years have tried to elucidate the exact molecular mechanisms involved in regulation of their expression. We have demonstrated previously that PHOX2B regulates the transcription of the PHOX2A gene by directly binding and transactivating its promoter. We also characterized PHOX2B promoter and demonstrated by means of biochemical and functional assays that most of its transcriptional activity is sustained and maintained by an auto-regulatory mechanisms in which PHOX2B binds and transactivates its own promoter. Chromatin immunoprecipitation (ChIP) assays showed that PHOX2A also participates in the transcriptional complex assembled on the PHOX2B promoter. The functional significance of this is under further investigation and the results of the various approaches used are the topic of the present poster.