TFE2 and GATA3 enhance induction of POU4F3 and myosin VIIa positive cells in nonsensory cochlear epithelium by ATOH1.

Transcription factors (TFs) can regulate different sets of genes to determine specific cell types by means of combinatorial codes. We previously identified closely-spaced TF binding motifs located 8.2-8.5 kb 5' to the ATG of the murine Pou4f3 gene, a gene required for late hair cell (HC) differentiation and survival. These motifs, 100% conserved among four mammalian species, include a cluster of E-boxes preferred by TCF3/ATOH1 heterodimers as well as motifs for GATA factors and SP1. We hypothesized that these factors might interact to regulate the Pou4f3 gene and possibly induce a HC phenotype in non-sensory cells of the cochlea. Cochlear sensory epithelium explants were prepared from postnatal day 1.5 transgenic mice in which expression of GFP is driven by 8.5 kb of Pou4f3 5' genomic DNA (Pou4f3/GFP). Electroporation was used to transfect cells of the greater epithelial ridge with multiple plasmids encoding human ATOH1 (hATOH1), hTCF3 (also known as E2A or TEF2), hGATA3, and hSP1. hATOH1 or hTCF3 alone induced Pou4f3/GFP cells but hGATA3 and hSP1 did not. hATOH1 but not hTCF3 induced conversion of greater epithelial ridge cells into Pou4f3/GFP and myosin VIIa double-positive cells. Transfection of hATOH1 in combination with hTCF3 or hGATA3 induced 2-3X more Pou4f3/GFP cells, and similarly enhanced Pou4f3/GFP and myosin VIIa double-positive cells, when compared to hATOH1 alone. Triple or quadruple TF combinations were generally not more effective than double TF combinations except in the middle turn, where co-transfection of hATOH1, hE2A, and hGATA3 was more effective than hATOH1 plus either hTCF3 or hGATA3. The results demonstrate that TFs can cooperate in regulation of the Pou4f3 gene and in the induction of at least one other element of a HC phenotype. Our data further indicate that combinations of TFs can be more effective than individual TFs in the inner ear.