The Notch ligand JAG1 is required for sensory progenitor development in the mammalian inner ear

Abstract

In mammals, six separate sensory regions in the inner ear are essential for hearing and balance function. Each sensory region is made up of hair cells, which are the sensory cells, and their associated supporting cells, both arising from a common progenitor. Little is known about the molecular mechanisms that govern the development of these sensory organs. Notch signaling plays a pivotal role in the differentiation of hair cells and supporting cells by mediating lateral inhibition via the ligands Delta-like 1 and Jagged (JAG) 2. However, another Notch ligand, JAG1, is expressed early in the sensory patches prior to cell differentiation, indicating that there may be an earlier role for Notch signaling in sensory development in the ear. Here, using conditional gene targeting, we show that the Jag1 gene is required for the normal development of all six sensory organs within the inner ear. Cristae are completely lacking in Jag1-conditional knockout (cko) mutant inner ears, whereas the cochlea and utricle show partial sensory development. The saccular macula is present but malformed. Using SOX2 and p27 kip1 as molecular markers of the prosensory domain, we show that JAG1 is initially expressed in all the prosensory regions of the ear, but becomes down-regulated in the nascent organ of Corti by embryonic day 14.5, when the cells exit the cell cycle and differentiate. We also show that both SOX2 and p27 kip1 are down-regulated in Jag1-cko inner ears. Taken together, these data demonstrate that JAG1 is expressed early in the prosensory domains of both the cochlear and vestibular regions, and is required to maintain the normal expression levels of both SOX2 and p27 kip1 . These data demonstrate that JAG1-mediated Notch signaling is essential during early development for establishing the prosensory regions of the inner ear. Citation: Kiernan AE, Xu J, Gridley T (2006) The Notch ligand JAG1 is required for sensory progenitor development in the mammalian inner ear. PLoS Genet 2(1): e4.

Sox2 and Jagged1 Expression in Normal and Drug-Damaged Adult Mouse Inner Ear

“…AB5603) and used at 1:1000. This antibody has been used on mouse (Ferri et al 2004;Kiernan et al 2006), and Western blot analyses carried out by the manufacturer on murine samples demonstrated that this antibody, at lower concentrations, recognizes a single protein of the correct size, approximately 34 kDa. The second anti-Sox2 antibody, an affinity purified goat polyclonal antibody directed against the C-terminus of human Sox2, was purchased from Santa Cruz (Sox-2 Y-17, Cat.…”

“…Western blot analyses carried out by the manufacturer on murine samples have demonstrated that this antibody, as well as the anti-Jagged1 (C-20) antibody discussed below, does not cross-react and recognizes a single protein of the correct size (150 kDa molecular weight). Others have used the H-114 antibody in mouse inner ear (Zine and de Ribaupierre 2002;Woods et al 2004;Kiernan et al 2006;Jones et al 2006). Jagged1 is an affinity purified goat polyclonal antibody raised against the C-terminus of human Jagged1.…”

“…Jagged1 and Sox2 have distinct tissue expression profiles in developing inner ear, and the specificity of the anti-Jagged1 and Sox2 antibodies has been demonstrated in developing mouse inner ear (Chen et al 2002;Zine and de Ribaupierre 2002;Woods et al 2004;Brooker et al 2006;Kiernan et al 2005aKiernan et al , 2006. Hence, P1-P5 inner ear tissue served as positive control tissue for these antibodies.…”

“…Jagged1 (referred to as Serrate 1 in chick and SerrateA or Jagged1b in zebrafish) is a member of the Notch signaling pathway, a pathway known to play a pivotal role in the differentiation of HCs and SCs (reviewed in Kelley 2006a, b). Jagged1 is expressed in prosensory regions of the ear before cell differentiation (Adam et al 1998;Morrison et al 1999;Kiernan et al 2006). Like Sox2, Jagged1 signaling is required for the development of inner ear sensory organs (Kiernan et al 2006).…”

“…Jagged1 is expressed in prosensory regions of the ear before cell differentiation (Adam et al 1998;Morrison et al 1999;Kiernan et al 2006). Like Sox2, Jagged1 signaling is required for the development of inner ear sensory organs (Kiernan et al 2006). It subsequently becomes restricted to the SCs, and its expression is maintained in auditory and vestibular SCs through the early postnatal period (Zine et al 2000;Woods et al 2004).…”