Early Embryology of the Vertebrate Ear

Molecular Genetics of Vestibular Organ Development

“…Experimental manipulations have established a critical role of the hindbrain in the development of the inner ear (for reviews, see Fritzsch et al 1998;Torres and Giraldez 1998;Fekete 1999;Anagnostopoulos 2002). Based on analyses of mutant and knockout mice, several genes expressed in the hindbrain have been shown to be required for normal development of the inner ear, including the vestibular system.…”

“…Normal development of the vertebrate inner ear depends on signals emanating from multiple surrounding tissues, including the hindbrain, neural crest, mesenchyme, and notochord (for reviews, see Fritzsch et al 1998;Torres and Giraldez 1998;Fekete 1999;Kiernan et al 2002). Primarily through the analyses of mutant mice with spontaneous mutations or targeted deletions (knockouts), several genes involved in the patterning of the inner ear have been identified.…”

Molecular Conservation and Novelties in Vertebrate Ear Development

“…Comparable to the octavolateralis hypothesis, this hypothesis assumes that the evolution of a mechanosensory transducer predates the evolution of a morphologically distinct vertebrate ear but does not require the prior evolution of a lateral line system. It thus circumvents some of the problems associated with the octavolateralis hypothesis while maintaining the basic idea that the evolution of mechanosensory transducers and their developmental molecular basis predates ear morphogenesis (Fritzsch et al, 1998a;Fritzsch et al, 2000). In line with this idea that ear neurosenory cell lineage formation predates morphogenesis are findings in the established outgroup of craniate vertebrates, the lancet Amphioxus.…”

“…Others have proposed that placodes undergo a stepwise refinement from a general placode system to a more specialized lateral line and ear placode system (Noramly and Grainger, 2002;Streit, 2002), but it is still unclear whether a common developmental program exists for the various sensory placodes (Begbie and Graham, 2001b;Groves and Bronner-Fraser, 2000). Still other work has shown that in many slowly developing vertebrates there are clear spatial and temporal differences in the development of lateral line and inner ear placodes, with the inner ear placode developing typically much earlier (Fritzsch et al, 1998a). Moreover, the uncoupling of lateral line from ear development during evolution has resulted in the complete loss of lateral line placodes in terrestrial vertebrates (Fritzsch, 1999;Schlosser, 2002).…”

“…Sensory cells without axons and the generation of a separate set of neurons that connect those sensory cells to the brain might therefore be ancestral features of vertebrates and possibly chordates ( Fig. 3) and are shared features of mechanosensory hair cells and taste receptors (Fritzsch et al, 1998a).…”