Lmx1a drives Cux2 expression in the cortical hem through activation of a conserved intronic enhancer.

Abstract

During neocortical development, neurons are produced by a diverse pool of neural progenitors. A subset of progenitors express the Cux2 gene and are fate-restricted to produce certain neuronal subtypes, but the upstream pathways that specify these progenitor fates remain unknown. To uncover the transcriptional networks that regulate Cux2 expression in the forebrain, we characterized a conserved Cux2 enhancer that we find recapitulates Cux2 expression specifically in the cortical hem. Using a bioinformatic approach, we found several potential transcription factor (TF) binding sites for cortical hem-patterning TFs. We found that the homeobox transcription factor, Lmx1a, can activate the Cux2 enhancer in vitro. Furthermore, we show that multiple Lmx1a binding sites required for enhancer activity in the cortical hem in vivo. Mis-expression of Lmx1a in neocortical progenitors caused an increase in Cux2+-lineage cells. Finally, we compared several conserved human enhancers with cortical hem-restricted activity and found that recurrent Lmx1a binding sites are a top shared feature. Uncovering the network of TFs involved in regulating Cux2 expression will increase our understanding of the mechanisms pivotal in establishing Cux2-lineage fates in the developing forebrain.\n\nSummary StatementAnalysis of a cortical hem-specific Cux2 enhancer reveals role for Lmx1a as a critical upstream regulator of Cux2 expression patterns in neural progenitors during early forebrain development.