Opposing activity of SOX9 and Wnt in the developing otocyst ensures SOX10 control of endolymphatic development
Sensorineural deafness can occur in campomelic dysplasia (CD). In a mouse model of the SOX9Y440X/+ CD mutation, SOX10 downregulation was previously shown to be associated with impaired development of the endolymphatic system at mid-gestation. The underlying molecular causes are unknown. Here we found at E10.5 when the otocyst lacks overt inner ear structures, Sox10 was downregulated in the dorsal and medial aspects of the Sox9Y440X/+ otic epithelium, regions associated with specification of the endolymphatic sac and duct.  Single-cell transcriptomic profiling revealed differential elevation of Wnt signaling pathway genes associated with the domain-specific Sox10 reduction. Otocyst-specific forced elevation of Wnt signaling by expression of stabilized ß-catenin suppressed Sox10 expression. Similarly, WNT exerted an inhibitory effect on SOX10 expression in human inner ear organoids derived from pluripotent stem cells. We propose a conserved regulatory model of SOX9-WNT antagonism governing SOX10 action in the otocyst underlies the specification of endolymphatic cell fate, with important implications for understanding human deafness syndromes. Overall design: E10.5 wild type and Sox9Y440X/+ (CD) otic vesicles (OVs) were isolated and dissociated for single-cell profiling. One additional replicate was included for the wild type.