The ETS transcription factor Etv1 mediates FGF signaling to initiate proneural gene expression during Xenopus laevis retinal development

• Etv1 is transiently expressed in the Xenopus laevis retina at the onset of neurogenesis.
• FGF signaling and etv1 expression are required for the expression of atonal-class proneural genes.
• Etv1 is required for retinal neuron differentiation.
• Activity of the atoh7 distal enhancer is dependent upon FGF signaling and etv1 expression.

Fibroblast growth factor signaling plays a significant role in the developing eye, regulating both patterning and neurogenesis. Members of the Pea3/Etv4-subfamily of ETS-domain transcription factors (Etv1, Etv4, and Etv5) are transcriptional activators that are downstream targets of FGF/MAPK signaling, but whether they are required for eye development is unknown. We show that in the developing Xenopus laevis retina, etv1 is transiently expressed at the onset of retinal neurogenesis. We found that etv1 is not required for eye specification, but is required for the expression of atonal-related proneural bHLH transcription factors, and is also required for retinal neuron differentiation. Using transgenic reporters we show that the distal atoh7 enhancer, which is required for the initiation of atoh7 expression in the Xenopus retina, is responsive to both FGF signaling and etv1 expression. Thus, we conclude that Etv1 acts downstream of FGF signaling to regulate the initiation of neurogenesis in the Xenopus retina.