Novel gene arrangement in the mitochondrial genome of the Cortés Geoduck clam (Panopea globosa).

The mitogenome of the Cortés geoduck clam Panopea globosa (Genbank accession KM580068) has a length of 15,469 bp and contains 13 protein-coding genes, 2 ribosomal RNA and 22 transfer RNA genes, as conventional metazoan mitochondrial genomes. Structural genes start with ATG, ATA and GTG codons; whereas TAG and TAA are used as stop codons. Base composition is: 23.3% A, 40.4% T, 10.1% C and 26.1% G. As is typical of marine bivalves, all genes are coded on the same strand. On the other hand, the gene arrangement is considerably different from those found in other heterodont bivalve mitogenomes.

The complete mitochondrial DNA of the Pacific Geoduck clam (Panopea generosa).

The complete mitochondrial genome of the Pacific Geoduck Panopea generosa (Genbank accession KM580067) is 15,585 bp in size and contains the typical 37 genes (13 protein-coding, 2 ribosomal RNA and 22 transfer RNA) found in metazoan mitogenomes, including the rare ATPase subunit 8 gene (ATP8). All genes are coded in the same strand but the gene arrangement is novel among heterodont bivalves. The base composition was: A 25.0%, T 38.7%, C 11.2% and G 25.0%. The genome is structurally similar to that of its congener the Cortes Geoduck Panopea globosa.

Odontogenesis in the Veiled Chameleon (Chamaeleo calyptratus).

OBJECTIVE: Replacement teeth in reptiles and mammals develop from a successional dental lamina. In monophyodont (single generation) species such as the mouse, no successional lamina develops. We have selected a reptilian monophyodont species - the Veiled Chameleon (Chamaeleo calyptratus) - to investigate whether this is a common characteristic of species that do not have replacement teeth. Furthermore, we focus on the sequence of tooth initiation along the jaw, and tooth attachment to the bones. DESIGN: Embryos of the Veiled Chameleon were collected during the first 6 months of incubation (from the 5th to 24th week) at 7-day intervals. RESULTS: After five weeks of incubation, an epithelial thickening was present as a shallow protrusion into the mesenchyme. A week later, the epithelium elongated more deeply into the mesenchyme to form the dental lamina. The formation of all tooth germs along the jaw was initiated from the tip of the dental lamina. Development of a successional dental lamina was initiated during the pre-hatching period but this structure became markedly reduced during juvenile stages. MicroCT analysis showed the presence of a heterodont dentition in young chameleons with multicuspid teeth in the caudal jaw area and simpler monocuspid teeth rostrally. Unlike the pleurodont teeth of most reptilian species, chameleon teeth are acrodontly ankylosed to the bones of the jaw. Odontoblasts produced a layer of predentine that connected the dentine to the supporting bone, with both tooth and bone protruding out of the oral cavity and acting as a functional unit. CONCLUSIONS: Chameleons may provide new and useful information to study the molecular interaction at the tooth-bone interface in physiological as well as pathological conditions.