Alterations in the incisor development in the Tabby mouse

The X-linked tabby (Ta) syndrome in the mouse is homologous to the hypohidr otic ectodermal dysplasia (HED) in humans. As in humans with HED, Ta mice e xhibit hypohidrosis, characteristic defects of hairs and tooth abnormalitie s. To analyze the effects of Ta mutation on lower incisor development, hist ology, morphometry and computer-aided 3D reconstructions were combined. We observed that Ta mutation had major consequences for incisor development le ading to abnormal tooth size and shape, change in the balance between prosp ective crown- and root-analog tissues and retarded cytodifferentiations. Th e decrease in size of Ta incisor was observed at ED13.5 and mainly involved the width of the tooth bud. At ED14.5-15.5, the incisor appeared shorter a nd narrower in the Ta than in the wild type (WT). Growth alterations affect ed the diameter to a greater extent than the length of the Ta incisor. From ED14.5, changes in the shape interfered with the medio-lateral asymmetry a nd alterations in the posterior growth of the cervical loop led to a loss o f the labio-lingual asymmetry until ED17.0. Although the enamel organ in Ta incisors was smaller than in the WT, a larger proportion of the dental pap illa was covered by preameloblasts-ameloblasts. These changes apparently re sulted from reduced development of the lingual part of the enamel organ and might be correlated with a possible heterogeneity in the development of th e enamel organ, as demonstrated for upper incisors. Our observations sugges t independent development of the labial and lingual parts of the cervical l oop. Furthermore, it appeared that the consequences of Ta mutation could no t be interpreted only as a delay in tooth development.