Hippo-dependent cell fate specification is antagonized by multiple regulatory modules. Baotong Xie¹, David Terrell^1,2,3, Mark Charlton-Perkins^1,2, Brian Gebelein^2,4, Tiffany Cook^1,2,4. 1) Division of Pediatric Ophthalmology, Cincinnati Childrens Hospital Medical Center, Cincinnati, OH 45229, USA; 2) Molecular and Developmental Biology Graduate Program, University of Cincinnati, Cincinnati, OH 45229, USA; 3) Physician Scientist Training Program, University of Cincinnati, Cincinnati, OH 45229, USA; 4) Division of Developmental Biology, Cincinnati Childrens Hospital Medical Center, Cincinnati, OH 45229, USA.

   The Warts/Lats kinase plays central roles in the Hippo signaling pathway for tissue growth and neurogenesis. In Drosophila, Warts forms a bistable negative feedback loop with the Melted pleckstrin homology-domain protein to govern blue vs green photoreceptor fate. How this loop is generated and leads to changes in cell fate remains unclear. Here, we describe a hierarchical transcriptional regulatory network that functions upstream, within, and downstream of the melted-warts bistable loop to promote blue- and repress green- photoreceptor fate. This network includes a conserved feedforward loop between OTX and MAF transcription factors, and a multi-level feedback loop between Warts, the TEA factor Scalloped and the Yorkie/YAP transcriptional co-activator. Integration and re-implementation of the same regulatory modules guarantees unambiguous fate decisions, thus regulating both cell fate determinants and terminal differentiation genes. Our study defines cell-autonomous transcriptional regulators that integrate with the Hippo pathway to ensure robust and stable neuronal fate decisions.