Expression and functions of FGF ligands during early otic development

Abstract

Classical studies have postulated the action of an endomesodermal signal initiating inner ear induction, subsequently followed by a neural tube-derived signal to complete the process of otic placode formation in the surface ectoderm. Members of the Fibroblast growth factor (FGF) gene family have been implicated in these processes. In this review, expression analysis and recent experimental evidence for candidate inner ear FGF ligands during inner ear induction is discussed. Careful examination of the spatiotemporal expression patterns of different FGFs during inner ear induction reveals that the sequential appearance of FGF members in the endoderm and/or mesoderm is followed by expression in the posterior hindbrain in all vertebrate species analysed to date. Experimental manipulations have demonstrated the sufficiency and/or necessity of some FGFs during different steps of inner ear induction in vitro and in vivo. Combining the advantages of the molecular tools and approaches available in different experimental systems such as zebrafish, chicken or mouse will eventually lead to a complete understanding of how FGFs control inner ear induction in vertebrates. KEY WORDS: inner ear, otic placode, fibroblast growth factor, otic inductionInner ear induction is already initiated during gastrulation by endomesodermal tissue which comes to underlie competent ectoderm. During neurulation, a second inducing neural signal from the presumptive hindbrain reinforces and maintains inner ear induction. The initial classical embryology experiments, addressing the sufficiency and necessity of different tissues during inner ear induction, have in more recent times been combined with molecular probes and tools to begin to build a molecular framework explaining different steps of inner ear induction (Baker and Bronner-Fraser, 2001;Noramly and Grainger, 2002;. Members of the Fibroblast growth factor (FGF) gene family are among the prime candidates to control inner ear induction since they show a spatiotemporal expression pattern consistent with playing a role during this process. Secondly, their inductive capacities and necessity during embryonic patterning and the formation of various organ systems underscores their potential to also participate during the early phases of inner ear formation (Reuss and von Bohlen und Halbach, 2003;Bottcher and Niehrs, 2005;Thisse and Thisse, 2005a). In this review the expression patterns of FGFs and the recent experimental evidence for their participation during inner ear induction is reviewed. Expression of FGFs during inner ear inductionIn this first section the spatiotemporal expression patterns of FGFs during inner ear induction in different vertebrate models is described. Following the experimental evidence that a first inductive Int. J. Dev. Biol. 51: 473-481 (2007) doi: 10.1387/ijdb.072334ts signal for otic placode formation is present in the endomesoderm we refer to this phase as the initiation of induction (Fig. 1A,D). The second phase of the induction process is initiated by a n...

Sox2 signaling in prosensory domain specification and subsequent hair cell differentiation in the developing cochlea

“…Additional work to identify other molecular components of the Sox2 pathway should identify crucial co-factors (20,21) that determine the different molecular effects of Sox2 in different cells and at different developmental time points during inner ear development. In addition to the upstream Notch signaling that we describe, it would be interesting to investigate whether Wnt and/or FGF signaling, both known to play early roles in inner ear development (22)(23)(24), also converge to activate Sox2 expression as they do in developing neural plate (25).…”

Effects of the Developmental Stage of Extract Donor Embryos on the Culture of Marine Medaka Oryzias dancena Embryonic Stem Cell-like Cells

“…, , (Catla catla; Dash et al, 2010) (Oryzias dancena; Lee et al, 2013) 7 , (Lateolabrax japonicas; Chen et al, 2003a) (Chrysophrys major; Chen et al, 2003b) 36 , (Scophtalmus maximus, Holen and Hamre, 2003) 3 . , , (Collodi and Barnes, 1990;Na et al, 2009), (Assouline et al, 2002;Maures et al, 2002;Schimmang, 2007;Hanington et al, 2008), .…”

Patterning and cell fate in ear development

“…The function of FGFs in otic development has been extensively studied. Several Fgfs are expressed in the hindbrain with species-specific patterns, and loss of function of Fgf genes leads to smaller and malformed otic vesicles, demon-strating a role for this signalling pathway in otic induction (for review see Schimmang, 2007). In zebrafish, this function is attributed mainly to FGF signals coming from the hindbrain, while in amniotes, other surrounding tissues such as the mesenchyme and endoderm are also sources of FGFs (Ladher et al, 2005;Freter et al, 2008).…”

“…FGF target genes are expressed in the otic epithelium, suggesting a direct effect of this signalling pathway (Chambers et al, 2000;Raible and Brand, 2001; Aragon and Pujades, unpublished results). The redundancy between different FGFs and their role in otic induction have hampered the analysis of their role in otocyst regionalisation (for review see Schimmang, 2007).…”