Roles of ß-catenin in inner ear development in rat embryos

Abstract

We studied the roles of beta-catenin in inner ear development in rat embryos using immunostaining and antisense experiments. High levels of beta-catenin appeared transiently in the otic cup during inner ear development. While beta-catenin accumulation was not yet observed in the thickened surface ectoderm at the otic placode, it became to be detected at the apical surface of the otic cup. Then it disappeared from the otocyst. When embryos were treated with the beta-catenin antisense oligodeoxynucleotide (ODN), accumulation of beta-catenin in the otic cup was suppressed and the beta-catenin protein level was significantly less in treated embryos than in controls. The number of cells in the otic cup in treated embryos was smaller than in control embryos. Cells that incorporated bromodeoxyuridine (BrdU) in the otic placode were fewer in number in treated embryos than in controls. In control embryos, acoustic neurons were detected by 2H3 (anti-neurofilament 165 kDa antibody) staining within the acoustic neural crest complex, while only a little staining of 2H3 was observed in the complex of the treated embryos. These results suggested that beta-catenin plays a role in cell proliferation in the otic placodes and in differentiation of acoustic neurons within the acoustic neural crest complex.

A direct role for Fgf but not Wnt in otic placode induction

“…Indeed, TOPdGFP expression is first detected in prospective otic ectoderm between 12-13 hpf (6-8 somites), just prior to morphological formation of the otic placode (data not shown). This is also consistent with the observation that, in rat, periotic accumulation of nuclear β-catenin is first detected just after formation of the otic placode (Matsuda and Keino, 2000). In addition, secreted Frizzled proteins, which are induced by Wnt signaling, are expressed in chick otic tissue only after formation of the otic placode Ladher et al, 2000b;Esteve et al, 2000;Terry et al, 2000).…”

Redundant functions of Rac GTPases in inner ear morphogenesis

“…First, we examined whether canonical Wnt/β-catenin signaling was affected in the Rac1 CKO ; Rac3 -/- otocyst. Previous studies in mice have shown that Wnt / β - catenin signaling is critical for both the proliferation and survival of otocyst cells (Matsuda and Keino, 2000; Ohyama et al, 2006). Wnt/β-catenin signaling is active in the dorsomedial otocyst, where it is required for the expression of dorsally expressed genes essential for vestibular morphogenesis (Hatch et al, 2007; Ohyama et al, 2006; Riccomagno et al, 2005).…”

“…Although Cyclin D1 expression level in the Rac1 CKO ; Rac3 -/- otocyst remains to be determined, a recent study reported decreased Cyclin D1 transcript levels in the Rac1 -deficient forebrain (Leone et al, 2010). Moreover, we investigated several other pathways implicated in otic cell proliferation including canonical Wnt/β-catenin, Eya1/Six1 and Sonic Hedgehog (Shh) (Matsuda and Keino, 2000; Ohyama et al, 2006; Riccomagno et al, 2002; Riccomagno et al, 2005; Xu et al, 1999; Zhao et al, 2006; Zheng et al, 2003; Zou et al, 2006). By monitoring reporter activity and target gene expression, we show that these pathways were unaffected in the Rac1 CKO ; Rac3 -/- otocyst, suggesting that Rac proteins are unlikely to mediate these mitogenic pathways.…”

Mapping of Wnt, frizzled, and Wnt inhibitor gene expression domains in the avian otic primordium

“…Misexpression of Wnt4, which is normally restricted to the ventral otocyst in frogs, leads to brain defects and lateral displacement of the otocyst in zebrafish and Xenopus (Ungar et al, 1995). Interference with β-catenin mRNA levels by antisense oligos reduces cell proliferation and the number of otic ganglion neurons in the chicken inner ear (Matsuda and Keino, 2000). Data from our lab show that Wnt/β-catenin signaling can influence the decision between auditory and vestibular sensory fate (Stevens et al, 2003), although it is still unknown whether there is an endogenous Wnt ligand with a comparable function.…”