Gata3 directly regulates early inner ear expression of Fgf10

The analysis of Fgf10 mouse mutants has demonstrated a critical role for this ligand in neurosensory development of the vertebrate inner ear, and we have been looking to define the direct upstream regulators of Fgf10 in this sensory organ, as part of constructing the programme of early inner ear development. Through the analysis of reporter constructs in transgenic mouse embryos and neonatal mice, in this report we define a minimal 1400 bp enhancer from the 5' flanking region of Fgf10. This enhancer drives reporter transgene expression in a manner that recapitulates endogenous expression of Fgf10, from its initial onset in the invaginating otic placode and onwards throughout gestation, controlling Fgf10 expression in all developing sensory patches and in the developing VIIIth ganglion. This regulatory region includes three putative Gata3 binding sites that we demonstrate directly interacts with Gata3 protein through the DNA binding domain with differing affinities. Site directed mutagenesis of all three sites and functional testing in transgenic embryos using reporter transgenes reveals an absolute requirement for Gata3 in controlling Fgf10 expression. Transgenic analysis of individual Gata3 binding site mutations illustrates that only one of these binding sites is necessary for reporter expression. Together these data demonstrate that Gata3 directly activates Fgf10 in the early inner ear, and does so through a single binding site.