The molecular biology of ear development - "Twenty years are nothing"

Abstract

Views of classical biological problems changed dramatically with the rise of molecular biology as a common framework. It was indeed the new language of life sciences. Molecular biology increasingly moved us towards a unified view of developmental genetics as ideas and techniques were imported to vertebrates from other biological systems where genetics was in a more advanced state. The ultimate advance has been the ability to actually perform genetic manipulations in vertebrate organisms that were almost unthinkable before. During the last two decades these technical advances entered into and affected the research on ear development. These events are still very recent and have been with us for no longer than two decades, which is the reason for the title of this article. This new scenario forms the basis of the current and productive work of many laboratories, and this is what this Special Issue of The International Journal of Developmental Biology wants to show, presenting a snapshot of insights at the beginning of the 21st Century. In this article, we give an overview of the topics that are addressed in this Ear Development Special Issue, and also we take the opportunity to informally dig into the genealogy of some of those topics, trying to link the current work with some classical work of the past. KEY WORDS: cell fate, patterning, hair cell, otic neuron, morphogenesis, evolution, regenerationEach time is characterised by the field of possibility that defines not only the standing theories or beliefs, but also the nature of the objects which are accessible to analysis, the means to look at them and the way to observe and to talk about them. (Jacob, 1976) There has been a sustained interest in ear developmental biology all throughout the 20 th century. As with many other fields in biology and neurosciences, this interest is in part rooted in curiosity and in part is driven by the intent to understand and cure diseases. There is an immense catalogue of histological observations and clever experimental manipulations of the embryonic ear that have contributed to an increase in our knowledge of the development of the ear and that was able to paint a picture of ear development by the end of the eighties (see Rubel, 1978; and the report of the Holte Symposium (Cremers et al., 1987). The view at the end of the eighties, however detailed, remained descriptive and phenomenological: the gap between cells, genes and proteins was Int. J. Dev. Biol. 51: 429-438 (2007) still too large and many processes were unknown leaving "the widest gap to be filled… to understanding how cells with identical genomes may become differentiated" (Jacob, 1947). Thirty years elapsed from the publishing of the double helix in 1953 to the polymerase chain reaction (Saiki et al., 1985) and during this period of time the whole of biology was changed and set a new paradigm. Views of classical biological problems, changed dramatically with the rise of molecular biology as a common framework. It was indeed the new language of life scien...

Notch Signaling Alters Sensory or Neuronal Cell Fate Specification of Inner Ear Stem Cells

“…Neural and sensory cell progenitors in the otic placode during embryonic development (Fekete and Wu, 2002; Barald and Kelley, 2004; Giraldez and Fritzsch, 2007) can produce neurons and hair cells after they are separated and cultured apart from the embryo (Adam et al, 1998), and some reports have indicated that single progenitors can give rise to neurons and sensory epithelial cells in the inner ear (Satoh and Fekete, 2005). Progenitors in the otic placode give rise to all cells in the inner ear except the glial cells in the spiral ganglion, which are thought to be derived from neural crest (Neves et al, 2007).…”

Movement of the external ear in human embryo

“…The external ear is evidently recognizable after Carnegie stage (CS) 16, and its movement has been described in most embryology textbooks as well [1-5]. The external ears are contained in the lower neck region at CS 17.…”

Tbx1 and Brn4regulate retinoic acid metabolic genes during cochlear morphogenesis

“…A crucial phase in development of the sensory structures of the inner ear occurs as the otic epithelium acquires regional identity along its axes. Classic explant experiments by developmental biologists first suggested that otic patterning occurred in response to signals from surrounding tissues, and recent work has revealed much of the molecular basis of these interactions [for review see [ 1 - 3 ]]. For example, genetic studies in the mouse showed that genes expressed along the dorsoventral axis of the otic vesicle are induced by signals from the roof plate and floor plate of the neural tube [ 4 , 5 ].…”