Notch signaling and Atoh1 expression during hair cell regeneration in the mouse utricle

Abstract

The mammalian vestibular epithelium has a limited capacity for spontaneous hair cell regeneration. The mechanism underlying the regeneration is not well understood. Because the Notch signaling pathway mediates the formation of the sensory epithelial mosaic patterning during ear development, it may also play a role in hair cell regeneration in the mature mammalian vestibular epithelium after a lesion. To investigate the process of spontaneous regeneration in the vestibular epithelium vis-à-vis changes in Notch signaling, we induced a unilateral lesion by infusing streptomycin into the mouse posterior semicircular canal, and examined Notch signaling molecules and their mRNA expression levels by immunohistochemistry and quantitative real-time polymerase chain reaction (qRTPCR), respectively. We detected Jagged1 in supporting cells in both normal and lesioned utricles. Atoh1, a marker for early developing hair cells, was absent in the intact mature tissue, but re-appeared after the lesion. Many cells were either positive for both Atoh1 and myosin VIIa, or for one of them. qRTPCR data showed a post trauma decrease of Hes5 and an increase in Atoh1. Atoh1 up-regulation may either be a result of Hes5 down-regulation or mediated by another signaling pathway.

Gene-expression analysis of hair cell regeneration in the zebrafish lateral line

“…In contrast to zebrafish, the Notch target genes are decreased only modestly, and Notch signaling is still active, in hair cell-depleted neonatal mouse cochleae and 3-to 4-wk-old mouse utricles (55,56,61). Therefore we hypothesize that the failure of transient Notch down-regulation in mammals could be one of the reasons that mammalian hair cells do not regenerate spontaneously after injury.…”

“…In zebrafish, Notch signaling is transiently down-regulated 1 h after hair cell death, correlating with the attenuation of sox2 and up-regulation of atoh1a. The interactions between Notch signaling, sox2, and atoh1a have not yet been tested in the zebrafish lateral line; however, because of their behavior during regeneration, it is very likely that their regulation is similar to that occuring during mouse, Xenopus, and zebrafish central nervous system or sensory organ development (23,52,61,(91)(92)(93). During murine ear development Sox2 expression depends on Notch signaling and is required for the acquisition of neural potential in the prosensory epithelium (52).…”

Sensory hair cell development and regeneration: similarities and differences

“…These studies have shown, for example, that hair cell damage in the avian cochlea and utricle, as well as in the zebrafish lateral line, results in the upregulation of Notch target genes (Daudet et al, 2009;Ku et al, 2014;Ma et al, 2008;Stone and Rubel, 1999). Furthermore, although the regenerative capacities of the mammalian cochlea and utricle are limited, the expression of Notch target genes in both of these organs also increases after damage (Batts et al, 2009;Korrapati et al, 2013;Lin et al, 2011;Mizutari et al, 2013;Wang et al, 2010).…”

Notch signaling prevents mucous metaplasia in mouse conducting airways during postnatal development

“…(1:400, Abcam); rabbit anti-HNF-3g (Foxa3) (1:100, Santa Cruz); rabbit anti-GFP (1:500, Invitrogen); rabbit anti-Hes5 (1:200, Chemicon) (Batts et al, 2009;El-Hashash et al, 2011;Li et al, 2009;Wang et al, 2010). Immunofluorescence was performed using secondary antibodies conjugated to Alexa Fluor 488 or 596 (1:200, Invitrogen) and analyzed using a Zeiss confocal laser-scanning microscope (LSM510 META) as previously described .…”