Hesr1 and Hesr2 may act as early effectors of Notch signaling in the developing cochlea.

In cochlear development, the Notch signaling pathway is required for both the early prosensory phase and a later lateral inhibition phase. While it is known that Hes genes are important downstream mediators of Notch function in lateral inhibition, it is not known what genes function as mediators of the early prosensory function of Notch. We report that two members of the Hes-related gene family, Hesr1 and Hesr2, are expressed in the developing cochlea at a time and place that makes them excellent candidates as downstream mediators of Notch during prosensory specification. We also show that treatment of cochlear explant cultures at the time of prosensory specification with a small-molecule inhibitor of the Notch pathway mimics the results of conditional Jag1 deletion. This treatment also reduces Hesr1 and Hesr2 expression by as much as 80%. These results support the hypothesis that Hesr1 and Hesr2 are the downstream mediators of the prosensory function of Notch in early cochlear development.