Epithelium-Mesenchyme Interactions

Also from studies of physiological airway repair, it is well known that the interaction between epithelium and mesenchymal elements such as fibroblasts is essential, and an abnormal response of this epithelial-mesenchymal trophic unit has been proposed to be central to the airway pathology and physiology characteristic of asthma [47]. 

FIGURE 61.2 Stages of tooth development A schematic frontal view of an embryo head at embryonic day (E)l 1.5 is shown with a dashed box to indicate the site where the lower (mandibular) molars will form. Below, the stages of tooth development are laid out from the first signs of thickening at El 1.5 to eruption of the tooth at around 5 weeks after birth. The tooth germ is formed from the oral epithelium and neural-crest-derived mesenchyme. At the bell st e of development, the ameloblasts and odontoblasts form in adjacent layers at the site of interaction between the epithelium and mesenchyme. These layers produce the enamel and dentin of the fully formed tooth. (Reproduced from Tucker, A. and Sharpe, P. Nat. Rev. Genet. 5 499-508,2004. With permission.)... 

Antagonistic interactions between FGF and BMP signals have been invoked as one possible mechanism for positioning tooth sites (Neubiiser et al. 1997), while the function of Bgf-8 as an inducer of known markers in the rostral mesenchyme (Tucker et al. 1999) may be involved in tooth type specification at the earlier stages. The latter experiments demonstrated that, at least, localised signal expression in the epithelium directs rostro-caudal patterning within the mandibular arch, rather than putative prespecification of cranial neural crest cells (Tucker et al. 1999). 

Crucial to the suggested interaction of epithelium and mesenchyme in fibrosis is the growth fector TGF-p. This fector is involved in normal alveolar development and regulation of repair processes in addition to its broad activities... 

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