Comparative histochemical studies on the development of teeth in man and in the mouse

Genetic diversity and recombination between turnip yellows virus strains in Australia

Disease outbreaks caused by turnip yellows virus (TuYV), a member of the genus Polerovirus, family Luteoviridae, regularly occur in canola and pulse crops throughout Australia. To understand the genetic diversity of TuYV for resistance breeding and management, genome sequences of 28 TuYV isolates from different hosts and locations were determined using high-throughput sequencing (HTS). We aimed to identify the parts of the genome that were most variable and clarify the taxonomy of viruses related to TuYV. Poleroviruses contain seven open reading frames (ORFs): ORF 0-2, 3a, and 3-5. Phylogenetic analysis based on the genome sequences, including isolates of TuYV and brassica yellows virus (BrYV) from the GenBank database, showed that most genetic variation among isolates occurred in ORF 5, followed by ORF 0 and ORF 3a. Phylogenetic analysis of ORF 5 revealed three TuYV groups; P5 group 1 and group 3 shared 45-49% amino acid sequence identity, and group 2 is a recombinant between the other two. Phylogenomic analysis of the concatenated ORFs showed that TuYV is paraphyletic with respect to BrYV, and together these taxa form a well-supported monophyletic group. Our results support the hypothesis that TuYV and BrYV belong to the same species and that the phylogenetic topologies of ORF 0, 3a and 5 are incongruent and may not be informative for species demarcation. A number of beet western yellow virus (BWYV)- and TuYV-associated RNAs (aRNA) were also identified by HTS for the first time in Australia.

The extracellular matrix of the dental pulp and dentin

The dental pulp is a loose connective tissue, characterized by its specific anatomical location. Its extracellular components are obvious subjects for study, since such components are largely responsible for the physiological properties of the tissue. Several clinically important processes occur extracellularly, e.g., defense mechanisms such as inflammatory reactions and formation of calcified tissue. The dental mesenchyme has a crucial role during early tooth morphogenesis. The dental pulp, or rather the dental papilla, seems to have only an indirect role during dentinogenesis. This review discusses proteoglycans and glycosaminoglycans, fibronectin and other non-collagenous proteins, and the different types of collagen that have been studied in pulp connective tissue. With regard to its biochemical constituents, the pulp is similar to other loose connective tissues. Collagen type I is the major fibrous component, but collagen type III also constitutes a large portion. Fibronectin is present, as is a high content of proteoglycan. In the proteoglycans, all normally occurring connective tissue glycosaminoglycans can be demonstrated. The composition of the pulpal extracellular matrix during tooth development is quite different from that of the mature tooth. Thus, it is important not to draw any too-far-reaching conclusions about the situation in human pulp from results obtained by studying pulp from animal teeth with ongoing dentinogenesis. In spite of their common ancestry, pulp and dentin differ considerably in extracellular matrix composition. Proteoglycans and collagen type I are present in dentin. No type III collagen or fibronectin can be found in the dentin, although it is present in the dental pulp.(ABSTRACT TRUNCATED AT 250 WORDS)

Human dentition and experimental animals

A review of the recent literature concerning enamel maturation patterns following cessation of protein matrix secretion confirms that developing rodent enamel exhibits an overall mineral distribution different from that of developing enamel in man, monkey, dog, and swine. This seems to be a result of structural differences of the enamel as the pattern of crystal growth appears similar in these species. Whether the differences in enamel structure are reflected in significant differences in cellular events leading to enamel formation and mineralization remain unknown, as detailed radioautographic and ultrastructural studies almost always have dealt with rodent teeth. It is therefore concluded that such studies should be initiated in experimental animals having an enamel formation and mineralization pattern strictly comparable to that of man. Some requirements for such an experimental animal are suggested.

Histochemical and radiologic studies of the human fetal mandibular condyle

Histochemical investigations on the mandibular condyle were performed on 72 human embryos and fetuses of crown-rump lengths (CRL) ranging from 26 to 186 mm, representing skeletal maturity indices expressed in CNO values (CNO = composite number of ossified bones in the hand and foot) ranging from 0-0 to 19-12. The development of the mandibular condyle is described according to morphology and to histochemical reactions for glycosaminoglucuronglycans, collagen, glycogen, alkaline and acid phosphatase, and nonspecific AS esterase. The development is described for (1) the bony component of the mandibular condyle, (2) the condylar cartilage, and (3) the fibrous cover of the mandibular condyle. For each tissue component, maturation steps are set up and included in the total evaluation of the condylar maturity stages. The developmental sequence set up on the basis of the morphologic and histochemical findings was followed by all condyles investigated. From this it may be presumed that the developmental sequence in human mandibular condylar components is constant during the former half of the prenatal period. The material available did not justify a description of skeletal development in the mandibular condyle as a function of fetal size, CRL, or skeletal maturity in the hand and foot.

Cathepsin D activity in isolated odontoblasts

The presence of an acid proteinase with a high activity has been demonstrated in isolated odontoblast-predentine material from dentinogenically active rat incisors. The enzyme was identified as cathepsin D (EC 3.4.23.5). The possible significance of the enzymatic degradation of proteoglycans and glycosaminoglycans in the course of the calcification process is discussed.