Abstract
Proper development of the inner ear, including specification and differentiation of progenitors for the endolymphatic sac, is crucial for hearing and balance. In a mouse model of the
SOX9
Y440X/+
mutation that causes campomelic dysplasia and deafness, impaired development of the endolymphatic system at mid-gestation was associated with SOX10 downregulation. The underlying molecular causes and significance are unclear. Here, we found in
Sox9
Y440X/+
mice,
Sox10
expression was downregulated, prior to overt differentiation, in the dorsomedial aspect of the E10.5 otic vesicle that normally becomes the endolymphatic duct and sac. Single-cell transcriptomic profiling of E10.5 otic vesicles showed increased expression of Wnt pathway genes that was associated with the domain-specific decrease in
Sox10
expression. Forced elevation of Wnt signaling by expression of stabilized β-catenin in the early otocyst and more developed inner ears, suppressed
Sox10
expression. Wnt exerted an inhibitory effect on
SOX10
expression in otocyst-like organoids derived from human pluripotent stem cells. In vitro transactivation assays reveal antagonistic action of SOX9 and Wnt signaling on
Sox10
transactivation mediated by conserved enhancers with neighboring/overlapping SOX9- and TCF/LEF-binding (Wnt effectors) motifs. We propose a conserved SOX9-Wnt antagonism acting via conserved enhancers, regulates SOX10 to modulate endolymphatic cell fate. The
SOX9
Y440X/+
mutation disrupts this regulatory circuit through both dominant-negative and haploinsufficient effects culminating in impaired establishment of progenitors in the otocyst that are essential for the development of the endolymphatic system for hearing and balance.