Domain-specific mechanisms of YAP1 variants in ocular coloboma revealed by in-vitro and organoid studies.

The conserved transcriptional co-activator YAP1 is a central regulator of organ development and tissue homeostasis, integrating mechanical and biochemical cues to control cell proliferation and survival. YAP1 variants underlie a spectrum of congenital disorders, including autosomal dominant ocular coloboma with or without syndromic features. Despite this clinical significance, the functional role of YAP1 in human eye development, as well as the impact of disease-associated missense variants, remains poorly understood. We show YAP1 expression at the optic fissure in human embryos, a key structure involved in coloboma pathogenesis. Using in silico prediction, cell-based assays, and fluorescence cross-correlation spectroscopy (FCCS) to directly quantify YAP1-TEAD binding, we demonstrate that the position of YAP1 missense variants dictates their functional changes. TEAD-binding domain mutations most strongly disrupted transcriptional activity in a luciferase assay, whereas all tested variants impaired induction of endogenous YAP1-TEAD target genes. Furthermore, mimicking reduced YAP1-TEAD binding using verteporfin small molecule in retinal organoids led to reduced progenitor proliferation and survival. These findings establish defective YAP1-dependent transcription as a mechanism driving congenital eye malformations and provide a framework for interpreting the pathogenicity of human YAP1 variants. More broadly, they highlight the need for functional analyses to connect genetic variation with disease.