Rat <Emphasis Type="Italic">wct</Emphasis> mutation prevents differentiation of maturation-stage ameloblasts resulting in hypo-mineralization in incisor teeth

A recent study provided genetic and morphological evidence that rat autosomal-recessive mutation, whitish chalk-like teeth (wct), induced tooth enamel defects resembling those of human amelogenesis imperfecta (AI). The wct locus maps to a specific interval of rat chromosome 14 corresponding to human chromosome 4q21 where the ameloblastin and enamelin genes exist, although these genes are not included in the wct locus. The effect of the wct gene mutation on the enamel matrix synthesis and calcification remains to be elucidated. This study clarifies how the wct gene mutation influences the synthesis of enamel matrix and its calcification by immunocytochemistry for amelogenin, ameloblastin and enamelin, and by electron probe micro-analysis (EPMA). The immunoreactivity for enamel proteins such as amelogenin, ameloblastin, and enamelin in the ameloblasts in the homozygous teeth was the same as that in the heterozygous teeth from secretory to transitional stages, although the homozygous ameloblasts became detached from the enamel matrix in the transitional stage. The flattened ameloblasts in the maturation stage of the homozygous samples contained enamel proteins in their cytoplasm. Thus, the wct mutation was found to prevent the morphological transition of ameloblasts from secretory to maturation stages without disturbing the synthesis of enamel matrix proteins, resulting in the hypo-mineralization of incisor enamel and cyst formation between the enamel organ and matrix. This mutation also prevents the transfer of iron into the enamel.     

Wear striations on the incisors of ceropithecid monkeys as an index of diet and habitat preference

Wear striations on the incisors of Old World monkeys were examined in order to determine associations between the distributions of striations, diet, and habitat preference. Significant differences exist between the Cercopithe-cinae and the Colobinae in respect to the orientation of incisor wear striations. In the Colobinae striations are oriented in a predominantly mesiodistal direction. In the Cercopithecinae striations usually have a labiolingual orientation. Comparisons of terrestrial and arboreal genera indicate that significant differences exist between the two groups in respect to the density of striations on the oc-clusal wear facets of maxillary central incisors. Arboreal and terrestrial monkeys also differ in the frequency of individual incisor wear facets completely devoid of wear striations.     

Incisor microwear of Sumatran anthropoid primates

Several studies have suggested that incisor microwear reflects diet and feeding adaptations of anthropoids. However, such studies have been largely qualitative, and interpretations have relied on anecdotal references to diet and tooth use reported in the socioecology literature. The current study relates incisor microwear in four anthropoid primates to specific ingestive behaviors and food types. Central incisor casts of wild-shot museum specimens of Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi were examined by scanning electron microscopy, and analyzed using a semiautomated image analysis procedure. Microwear patterns were used to generate predictions regarding diet and anterior tooth use. These predictions were evaluated using data collected during a 1 year study of feeding behavior of these same taxa in the wild (Ungar, 1992, 1994a, b). Results suggest that (1) enamel prism relief is associated with the effectiveness of etching reagents in foods, (2) dental calculus buildup results from a lack of incisor use and perhaps the ingestion of sugar-rich foods, (3) striation density varies with degree of anterior tooth use in the ingestion of abrasive food items, (4) striation breadth is proposed to relate to the ratio of exogenous grit to phytoliths consumed; and (5) preferred striation orientation indicates the direction that food items are pulled across the incisors during ingestion. It is concluded that incisor microwear studies can contribute to the understanding of diets and feeding behaviors of extinct primates. © 1994 Wiley-Liss, Inc.     

贵州普定穿洞出土的一化石智人颅盖骨

1976年南京大学地理系俞锦标教授等在贵州省普定县进行野外调查时,在穿洞发现骨化石、烧骨、灰烬等。后于1979年,在有关方面的配合下,在洞口进行试掘,掘到1.5米深处,获得了一个破碎的智人颅盖骨化石。颅盖骨附近还有右上颌骨半块、单独的右上中门齿一枚。与头骨化石共生的有一些骨角器、烧骨和少量石器。这些材料俞教授等已作过报道和初步研究(俞锦标等,1983;俞锦标,1984)。不久前,俞教授把头盖骨化石供本人作古人类学研究之用,现报告如下。     

Incisor-molar relationships in chimpanzees and other hominoids: implications for diet and phylogeny

In chimpanzees, the cutting edge of the incisor battery is longer in relation to the length of the molar row than in any other hominoid, extant or fossil, the only other lineage approaching it being the orangutan. Apart from their increased mesio-distal dimensions, the upper and lower incisors of chimpanzees differ in additional ways from those of almost all other hominoids. The I2/ is enlarged, so that the difference in size between it and the central upper incisor is less than it is in the heteromorphic upper incisors of other hominoids. The lower incisors are expanded mesio-distally, so much so that isolated I/2 crowns can resemble upper central incisors. In chimpanzees the lingual surface of the lower incisors is generally more procumbent than it is in other hominoids, which have more vertically oriented incisor crowns and there is a greater difference in enamel thickness between labial and lingual sides. The re-orientation of the lower incisor crown is reflected in the root, which in lateral view is anteriorly concave in chimpanzees whereas it is more orthogonal or convex in other hominoids. The molars of chimpanzees, especially the lowers, have extensive and relatively deep occlusal basins, and the main cusps are peripheralised and labio-lingually compressed, making them more trenchant than those of other hominoids. This paper examines the incisor-lower molar proportions in extinct and living hominoids and develops a new hypothesis about the evolution of the dentition of chimpanzees and links it to their diet. It also examines the incisor-molar proportions of hominids and African apes in order to throw light on the phylogenetic relationships between them. It is shown that chimpanzees are highly derived in this respect and that several recent ideas concerning the chimp-like appearance of the last common ancestor of hominids and African apes are likely to be incorrect.This revised version was published online in April 2005 with corrections to the cover date of the issue.     

The depth of the lingual fossa in permanent incisors of Norwegians. II. Differences between central and lateral incisors correlations, side asymmetry and variability

The depth of the lingual fossa in permanent incisors of Norwegians (plaster casts and extracted teeth) was studied. In the plaster casts the depth of the lingual fossa in the right side incisors was (in mm): I,sup=0.51,I(2)sup= 0.30, I(1)inf =0.07 and I (2)inf =0.08. For 1(1)sup significant bilateral asymmetry was found (p<0.00l). All incisors were positively correlated in the depth of the lingual fossa, mandibular higher than maxillary. In both jaws centrals were better correlated across the midline than laterals, and centrals to laterals were less correlated than centrals to centrals and laterals to laterals. Interjaw correlations of 1(1)sup were higher than interjaw correlations with I(2)sup. Dental field theory is confirmed: The upper lateral and lower central were the most variable incisors in each jaw for lingual fossa depth. The values for this trait in Norwegians are within the Caucasoid range.     

The depth of the lingual fossa in permanent incisors of Norwegians. I. Method of measurement, statistical distribution and sex dimorphism

The depth of the incisor lingual fossa in permanent extracted incisors and plaster casts of Norwegians was examined. It was shown that plaster casts are well suited for measurements of lingual fossa depth, and that the measurements can be performed with great accuracy. Skewness values showed the symmetry of the distribution to decrease with decreasing mean lingual fossa depth. Kurtosis was found small in maxillary incisors, in mandibular outside the limits for normal theory. The distribution of the depth of the lingual fossa cannot generally be described as normal. No sex differences were found. The inheritance of this trait in Norwegians is probably not sex linked.     

TGF-β superfamily signaling is essential for tooth and hair morphogenesis and differentiation

Members of the transforming growth factor β (TGF-β) superfamily of signaling molecules are involved in the regulation of many developmental processes that involve the interaction between mesenchymal and epithelial tissues. Smad7 is a potent inhibitor of many members of the TGF-β family, notably TGF-β and activin. In this study, we show that embryonic overexpression of Smad7 in stratified epithelia using a keratin 5 promoter, results in severe morphogenetic defects in skin and teeth and leads to embryonic and perinatal lethality. To further analyze the functions of Smad7 in epithelial tissues of adult mice, we used an expression system that allowed a controlled overexpression of Smad7 in terms of both space and time. Skin defects in adult mice overexpressing Smad7 were characterized by hyper-proliferation and missing expression of early markers of keratinocyte differentiation. Upon Smad7-mediated blockade of TGF-β superfamily signaling, ameloblasts failed to produce an enamel layer in incisor teeth. In addition, TGF-β blockade in adult mice altered the pattern of thymic T cell differentiation and the number of thymic T cells was significantly reduced. This study shows that TGF-β superfamily signaling is essential for development of hair, tooth and T-cells as well as differentiation and proliferation control in adult tissues.