Conserved and distinct regulatory targets of Brn3a at different levels of the sensory axis

General somatic sensation is conveyed to the central nervous system at cranial levels by the trigeminal ganglion (TG), and at spinal levels by the dorsal root ganglia (DRG). Although these ganglia have similar functions, they have distinct embryological origins, in that both contain neurons originating from the neural crest, while only the TG includes cells derived from the placodal ectoderm. Here we use microarray analysis of E13.5 embryos to demonstrate that the developing DRG and TG have very similar overall patterns of gene expression. In mice lacking the POU-domain transcription factor Brn3a the DRG and TG exhibit many common changes in downstream gene expression, but a subset of genes show increased expression only at cranial levels. Although silent in wild-type ganglia, the promoter regions of genes which are activated in the absence of Brn3a also exhibit increased histone H3-acetylation at levels similar to constitutively transcribed gene loci, and this H3-acetylation is tissue-specific for genes which are increased only in the TG. These results demonstrate that one developmental role of Brn3a is to repress potential differences in gene expression between sensory neurons generated at different axial levels, and to regulate a convergent program of developmental gene expression, in which functionally similar populations of neurons are generated from different embryological substrates. Keywords: Gene expression in the developing nervous system Microarrays used to compare the patterns of gene expression in the dorsal root ganglia and trigeminal ganglia of Brn3a knockout and wild-type mice. Embryonic day 13.5 (E13.5) was chosen because at this point in development mutant mice exhibit major defects in sensory axon growth, but have yet to undergo the period of extensive sensory neuron death associated with later stages.