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P11 Morphological evidence for the role of epithelial tissue during mouse tongue development.

We investigated the basic processes of development of tongue papillae as part of a study aimed at understanding epithelial-mesenchymal interactions during mouse embryonic development. 
 
Using scanning electron microscopy (SEM) and histological methods we examined the morphological changes associated with normal development of tongue papillae. From embryonic day 12 (E12) to E17, morphogenesis of fungiform papillae occurs in a stereotyped pattern on the dorsal surface of the tongue. Development of fungiform papillae began with epithelial thickening and then formed a concave structure of epithelium and condensed mesenchyme. Formation of tongue papillae shared a pattern of morphological change similar to other epithelial appendages. 
 
We examined expression of the signalling molecules bmp2, bmp4 and shh which are known to play an important role in development of other epithelial appendages. At E12 bmp2, bmp4 and shh had a broad distribution on the dorsal surface of the tongue, restricted to the epithelial layer. At E13 signalling molecules were expressed in a restricted region of the dorsal epithelium. 
 
E14 expression of bmp2 and bmp4 had decreased but shh was maintained and had a punctate pattern in the epithelium. By comparing the SEM and histological studies, we recognised that the regions expressing bmp2, bmp4 and shh coincided with the regions of fungiform papillae formation. 
 
In summary, development of fungiform papillae should be a useful model for studying epithelial-mesenchymal interactions.