Role of diffusible and transcription factors in inner ear development: implications in regeneration

Organogenesis involves a dynamic balance of the mechanisms regulating cell division, differentiation and death. The development of the chicken embryo inner ear offers a well-characterised model at the morphological level to s tudy which signals are implicated in the modulation of cellular activation and commitment. The early developmental decisions that control the origin o f the inner ear elements are just beginning to be identified by complementa ry in vivo and in vitro studies. Insulin-like growth factor-I (IGF-I) and n erve growth factor (NGF) are among the best characterised diffusible factor s acting during inner ear development. Although the cellular actions of the se factors are beginning to be understood, the signalling pathways triggere d by them still remain largely unknown. In this context, viral vehicles can be used to deliver genes and then analyse their functional roles during in ner ear development. A model is proposed where the actions of IGF-I and NGF contribute to the combinatorial expression of Jun and Fos family members i n particular domains of the otic vesicle. Some of these mechanisms may be a lso implicated in otic regeneration.