Hes1, Hes5, and Hey1 are three of the important Notch downstream transcription factors, and knock-out of Hes1, Hes5, and Hey1 in the inner ear also results in extra HCs [89–92], which is consistent with our results, and thus down-regulation of Hes1, Hes5, and Hey1 by Foxg1 cKD might contribute to the phenotype of extra HCs. Here, HEY1 is linked to chronic kidney disease.