Role of Jagged1 in cochlear supporting cell differentiation and maintenance

Inner ear cochlear supporting cells (SCs) are highly specialized glia-like cells that structurally and functionally support neighboring mechano-sensory hair cells. Despite their importance for proper auditory function, little is known about the molecular mechanisms that control their development. In this study we investigated the function of the Notch ligand Jagged1 (Jag1) in cochlear SC differentiation and maintenance. To address the function of Jag1 in the differentiation of SCs, we conditionally deleted Jag1 in stage E14.5 SC precursors using the recently established Sox2-CreER/+ and Jag1 fx/fx mouse lines. Analysis of stage P0 Jag1 mutant and control animals revealed that Hensen cells, a highly specialized SC-subtype located at the lateral edge of the auditory sensory epithelium, failed to form in the absence of Jag1. Other SC-subtypes did form in the absence of Jag1, however, their morphology and cellular arrangement was abnormal and SC-subtype specific genes and genes associated with mitochondrial function and protein synthesis were significantly reduced, indicating global defects in SC differentiation and SC homeostasis. To delete the Jag1 gene at the onset of supporting cell differentiation, we co-administered tamoxifen and progesterone to pregnant dams at stage E14.5. Five days later we harvested cochlear epithelia from P0 Sox2-CreER/+ Jag1 fx/fx (Jag1 mutant) and Jag1 fx/fx (Jag1 wild type) mice, isolated total RNA and analyzed gene expression using Clariom D arrays. The three biological replicates of each class, mutants and wildtype controls, were compared.