Sufu controls the proliferation and differentiation of cochlear prosensory progenitors

Abstract

During inner ear development, prosensory progenitors exit cell cycle before E14.5. Later, some progenitors express Atoh1 and differentiate into hair cells. Loss-of-function analysis suggests that Shh controls the timing of hair cell differentiation. However, little is known about the roles of the downstream mediators of Shh signaling in cochlear hair cell progenitors. Gli transcription factors regulate the expression of downstream genes, while Suppressor-of-fused (Sufu) modulates the transcriptional activity, stability and processing of Gli in some tissues. To understand the function of Sufu in prosensory progenitors, Pax2-cre; Sufuf/f mutant with Sufu deleted in the inner ear was generated. By immunostaining, four rows of hair cells were observed at the medial region of E16.5 control cochlea but hair cell was not found at the similar region of Sufu-null mutant, indicating severely delayed hair cell differentiation. Since Gli3 repressor level significantly reduced in the absence of Sufu, Gli3P1-4/P1-4 mutant that produced no Gli3 repressor protein was studied. The progression of hair cell differentiation was also delayed in Gli3P1-4/P1-4 mutant ear. These showed that Sufu modulated the differentiation of hair cell progenitors via Gli3 repressor. As defects in differentiation may be due to impaired progenitor specification and proliferation, immunostaining of Sox2, p27 and BrdU was performed. In the E14.5 Sufu mutant, Sox2 and p27 were expressed at the ventral cochlear epithelium. However, loss of Sufu resulted in more BrdU+ proliferating progenitors in the Sox2+ domain. Our data suggest that Sufu regulates both proliferation and differentiation of hair cell progenitors.