Amelogenesis imperfecta in the dentition of a wild chimpanzee

This report describes a case of amelogenesis imperfecta in the dentition of a female chimpanzee. Amelogenesis imperfecta is a group of rare genetic conditions that create severe enamel defects, which, although well researched in humans, has not yet been investigated in wild non‐human primates.     

Relationship of enamel hypoplasia to the pattern of tooth crown growth: A discussion

The defects of enamel hypoplasia can be related to the layered structure of enamel which represents the sequence of development in tooth crowns. From such studies, it is possible to see that furrow-type enamel defects (the most common form of hypoplasia seen with the naked eye) are just the most prominent expression of a continuum which extends ever smaller, down to a microscopic disturbance to a single layer in the crown formation sequence. Furthermore, the progressive decrease in spacing between development layers which occurs down the crown sides, from occlusal to cervical, affects both the prominence and apparent width of the defects. This makes it difficult to use measurements as a means of estimating the duration of the disturbance causing a particular defect. The difficulty is even greater for the less common pitted or exposed-plane-type defects, for which the apparent width bears very little relationship with the duration of the growth disturbance. The defects of enamel hypoplasia can therefore be understood clearly only when examined under the microscope in relation to the structures which mark the development sequence of the tooth crown. Am J Phys Anthropol 104:89–103, 1997. © 1997 Wiley-Liss, Inc.     

Sonic hedgehog signaling regulates Gli3 processing, mesenchymal proliferation, and differentiation during mouse lung organogenesis

Lack of Sonic hedgehog (Shh) signaling, mediated by the Gli proteins, leads to severe pulmonary hypoplasia. However, the precise role of Gli genes in lung development is not well established. We show Shh signaling prevents Gli3 proteolysis to generate its repressor forms (Gli3R) in the developing murine lung. In Shh(-/-) or cyclopamine-treated wild-type (WT) lung, we found that Gli3R level is elevated, and this upregulation appears to contribute to defects in proliferation and differentiation observed in the Shh(-/-) mesenchyme, where Gli3 is normally expressed. In agreement, we found Shh(-/-);Gli3(-/-) lungs exhibit enhanced growth potential. Vasculogenesis is also enhanced; in contrast, bronchial myogenesis remains absent in Shh(-/-);Gli3(-/-) compared with Shh(-/-) lungs. Genes upregulated in Shh(-/-);Gli3(-/-) relative to Shh(-/-) lung include Wnt2 and, surprisingly, Foxf1 whose expression has been reported to be Shh-dependent. Cyclins D1, D2, and D3 antibody labelings also reveal distinct expression patterns in the normal and mutant lungs. We found significant repression of Tbx2 and Tbx3, both linked to inhibition of cellular senescence, in Shh(-/-) and partial derepression in Shh(-/-); Gli3(-/-) lungs, while Tbx4 and Tbx5 expressions are less affected in the mutants. Our findings shed light on the role of Shh signaling on Gli3 processing in lung growth and differentiation by regulating several critical genes.     

Factors affecting the distribution of enamel hypoplasias within the human permanent dentition

Frequencies and morphological and chronological distributions of enamel hypoplasias are presented by tooth type (permanent I1 to M2s), based on a sample of 30 prehistoric Amerindians with complete and unworn dentitions. There is nearly a tenfold variation in frequency of defects by tooth, ranging from 0.13 per mandibular second molar to 1.27 per maxillary central incisor. The six anterior teeth average between 0.70 and 1.27 defects/tooth, whereas the eight posterior teeth average between 0.43 and 0.13 defects/tooth. Earlier developing teeth, such as incisors, have earlier peak frequencies of defects (2.0-2.5 years), while later developing teeth, such as second molars, have subsequent peak frequencies (5.0-6.0 years). These variations are relevant when comparing hypoplasia data based on different teeth. Differences in hypoplasia frequencies among teeth are not solely due to variation in time of crown development, as is usually reported. Rather, there is evidence for biological gradients in susceptibility to ameloblastic disruption. Anterior teeth are more hypoplastic than posterior teeth. More developmentally stable "polar" teeth are more hypoplastic than surrounding teeth. Polar teeth may be more susceptible to hypoplasias because their developmental timing is less easily disrupted. In all teeth, hypoplasias are most common in the middle and cervical thirds. Crown development and morphological factors, such as enamel prism length and direction, may influence the development and expression of enamel surface defects.