The vertebrate inner ear is a complex structure providing the sensory systems for detection of balance, acceleration and sound. During embryogenesis it originates from a simple epithelium, the otic placode, one of the neurogenic placodes in the head. The placode becomes first detectable as a thickening of the ectoderm in 8-10 somite embryos and embryological studies suggest that it arises through inductive interactions with surrounding tissues. The placode then invaginates to form the otocyst, which in a complex morphogenetic process generates the auditory and vestibular portions of the ear. In addition, the distal parts of the vestibular and cochlear ganglia are also derived from the otic placode. A considerable number of congenital craniofacial malformations in humans are associated with hearing impairment. In recent years, some of the genes underlying these complex syndromes have been identified and model systems in mice have been established. Most of these genes seem to be involved in patterning events within the otocyst. In contrast, our knowledge about the initiation of the otic placode is still very fragmentary and it seems that for successful induction signals from different tissues need to be integrated. This project aims to investigate the earliest steps in the induction and specification of the otic placode using the chick embryo as a model system. We will combine experimental embryology with molecular approaches to identify the future placode territory before it is specified and to characterize molecular markers for it. We will then establish when embryonic ectoderm is competent to respond to placode inducing signals and which tissues emit these signals. These studies will provide the basis to design screens to identify the molecular pathways involved in the induction of the otic placode.
| Streit, A (2001) Origin of the vertebrate inner ear: evolution and induction of the otic placode. J Anat 199:99-103 |
