Ultrastructure of Pleromin, a Highly Mineralized Tissue Comprizing Crystalline Calcium Phosphate Known as Whitlockite, in Holocephalian Tooth Plates

Ishiyama, Mikio; Souma, Yoshie; Teraki, Yoshimi; Cooper, E. W. T.

doi:10.1007/978-4-431-68132-8_72

Cited by 8 publications

(14 citation statements)

References 8 publications

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“…In holocephalans, teeth are specialized to form tooth plates, which largely consist of dentin (or a bone‐like tissue) and pleromin (Ørvig, ). Pleromin is the principal hypermineralized tissue in this clade, composed of whitlockite (instead of hydroxyapatite), and formed entirely by cells of mesenchymal origin (Ishiyama et al., , ). By contrast, enameloid is the hypermineralized tissue in elasmobranchs, but enameloid in elasmobranchs appears to be different from enameloid in teleosts in the ultrastructure (Bendix‐Almgreen, ), organic matrix, process of mineralization, and roles of epithelial cells (Sasagawa, , ).…”

Section: Discussionmentioning

confidence: 99%

SCPP Genes and Their Relatives in Gar: Rapid Expansion of Mineralization Genes in Osteichthyans

et al. 2017

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Gar is an actinopterygian that has bone, dentin, enameloid, and ganoin (enamel) in teeth and/or scales. Mineralization of these tissues involves genes encoding various secretory calcium-binding phosphoproteins (SCPPs) in osteichthyans, but no SCPP genes have been identified in chondrichthyans to date. In the gar genome, we identified 38 SCPP genes, seven of which encode "acidic-residue-rich" proteins and 31 encode "Pro/Gln (P/Q) rich" proteins. These gar SCPP genes constitute the largest known repertoire, including many newly identified P/Q-rich genes expressed in teeth and/or scales. Among gar SCPP genes, six acidic and three P/Q-rich genes were identified as orthologs of sarcopterygian genes. The sarcopterygian orthologs of most of these acidic genes are involved in bone and/or dentin formation, and sarcopterygian orthologs of all three P/Q-rich genes participate in enamel formation. The finding of these genes in gar suggests that an elaborate SCPP gene-based genetic system for tissue mineralization was already present in stem osteichthyans. While SCPP genes have been thought to originate from ancient SPARCL1, SPARCL1L1 appears to be more closely related to these genes, because it established a structure similar to acidic SCPP genes probably in stem gnathostomes, perhaps at about the same time with the origin of tissue mineralization. Assuming enamel evolved in stem osteichthyans, all P/Q-rich SCPP genes likely arose within the osteichthyan lineage. Furthermore, the absence of acidic SCPP genes in chondrichthyans might be explained by the secondary loss of earliest acidic genes. It appears that many SCPP genes expanded rapidly in stem osteichthyans and in basal actinopterygians.

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Section: Discussionmentioning

confidence: 99%

SCPP Genes and Their Relatives in Gar: Rapid Expansion of Mineralization Genes in Osteichthyans

et al. 2017

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“…The prelomin is a very unique hard tissue produced only from mesenchymal cells and consists of whitlockite (Ishiyama et al, 1984(Ishiyama et al, , 1991. This demonstrates that the mesenchymal cells themselves can form a well-mineralized hard tissue like enamel.…”

Section: Elasmobranch Enameloid Is Distinct From the Enameloid In Bonmentioning

confidence: 96%

“…This demonstrates that the mesenchymal cells themselves can form a well-mineralized hard tissue like enamel. The initial crystals in prelomin are formed in the tubular saccules limited by a unit membrane and derived from mesenchymal cells (Ishiyama et al, 1991). The tubular saccules are quite similar to the TVs in elasmobranch enameloid.…”

Section: Elasmobranch Enameloid Is Distinct From the Enameloid In Bonmentioning

confidence: 99%

Mineralization patterns in elasmobranch fish

Sasagawa

2002

Microscopy Res & Technique

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This article reviews current findings on the organic matrix and the mineralization patterns in elasmobranchs, including an analysis of the role of the dental epithelial cells and the odontoblasts during odontogenesis. Our electron micrographs demonstrated that tubular vesicles limited by a unit membrane occupied the bulk of the elasmobranch enameloid matrix during the stage of enameloid matrix formation. It is likely that the tubular vesicles originated from the odontoblast processes. Two types of electron-dense fibrils, with cross-striations at intervals of approximately either 17 nm or 55 nm, respectively, were detected in the enameloid matrix. These data suggest that odontoblasts were strongly involved in enameloid matrix formation and in initial enameloid mineralization. Two types of odontoblasts, dark and light cells, were recognized during the stage of dentinogenesis. The light cells contained numerous mitochondria, intermediate filaments, and microtubules that extended their processes into the dentin. The dark cells possessed a well-developed Golgi apparatus and many cisternae in the rough endoplasmic reticulum, which suggests that the dark cells are involved in the formation of dentin. The inner dental epithelial (IDE) cells exhibited a well-developed Golgi apparatus, many mitochondria, cisternae of smooth endoplasmic reticulum, vesicles, vacuoles, and granules during the mineralization and maturation stages. During the stages of mineralization and early maturation, ACPase-positive granules were visible in the IDE cells and ALPase and Ca-ATPase activities were found at the lateral and proximal cell membrane of the IDE cells, suggesting that the IDE cells are involved in the removal of enameloid organic matrix and in the process of mineralization during later stages of enameloid formation. Our data indicate that elasmobranch enameloid is distinct from teleost enameloid, based on its organic content, on the mechanisms of its mineralization, and on the role of IDE cells concerning enameloid formation.

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“…In the early stage of pleromin formation, initial crystals deposited in tubular saccules, which is the major constituents of the immature pleromin matrix 19 . The mineral deposition in tubular matrix is also detected by optic observation 11 .…”

Section: Discussionmentioning

confidence: 99%

“…Terms for these hard tissues are sometimes changed by various workers with new data 18 . In our study, we refer to the lightly mineralized bulky tissue as osteodentin, the hypermineralized pads and tritoral pad as vascular pleromin, and hypermineralized rods and ovoid as compact pleromin, following our previous papers 2 , 19 .…”

Section: Introductionmentioning

confidence: 99%

A unique mineralization mode of hypermineralized pleromin in the tooth plate of Chimaera phantasma contributes to its microhardness

Iijima¹,

Ishiyama²

2020

Sci Rep

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Tooth plates of the chimaeroids, holocephalian fishes, are unique dental hard tissues. Unlike the teeth of other animals, the tooth plates are located on the roof of the mouth and in the lower jaw. Their tooth plates consist, to a large extent, of lightly mineralized tissue (osteodentin) and hypermineralized tissue (pleromin). Notably, the mineral phase of pleromin is whitlockite, while that of other animals is apatite. Dietary habits of chimaeroids and wearing features of their tooth plates suggest an extreme hardness of pleromin, but this has never been investigated. We examined the microhardness of the tooth plate of Chimaera phantasma and found that pleromin in the biting region was extremely hard, comparable with the hardness of mature tooth enamel, whereas the hardness of immature pleromin was lower than that of bovine dentin. The hardness of osteodentin, on the other hand, was equivalent to that of bovine dentin and almost the same throughout the tooth plate. Immature pleromin was sparsely packed with oval crystals of whitlockite and, as pleromin matures, the space between crystals was filled with small intercrystalline materials. The maturing process of pleromin could partly contribute to its remarkable hardness and have some implications for designing novel biomaterials.

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Ultrastructure of Pleromin, a Highly Mineralized Tissue Comprizing Crystalline Calcium Phosphate Known as Whitlockite, in Holocephalian Tooth Plates

Cited by 8 publications

References 8 publications

SCPP Genes and Their Relatives in Gar: Rapid Expansion of Mineralization Genes in Osteichthyans

SCPP Genes and Their Relatives in Gar: Rapid Expansion of Mineralization Genes in Osteichthyans

Mineralization patterns in elasmobranch fish

A unique mineralization mode of hypermineralized pleromin in the tooth plate of Chimaera phantasma contributes to its microhardness

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