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Evolutionary scenario for the turnover of the jawed vertebrate ameloblastic genetic toolkit. The composition of the enamel/enameloid mineralization toolkit is shown for the hypothetical stem jawed vertebrates (A), holocephalans (B), elasmobranchs (C), and osteichthyans (D), whose odontodes contain a dentine core (Dn) covered by an enamel/enameloid layer (En). Arrows indicate the phosphorylation (P) of Sparc-L (orange) and/or Scpp (red) proteins by Fam20°C (yellow). Sparc-L harbors a C-terminal Kazal/calcium-binding domain (Ca2+) absent from Scpp proteins. The holocephalan Sparc-L N-terminal domain contains 11 tandem duplications of an acidic motif (vertical lines) enriched in SxE sites. A cladogram shows for each jawed vertebrate lineage the ameloblastic expression of sparc-L and scpp genes (orange and red branches, respectively). Asterisks indicate parallel scpp duplication events. According to this model the ancestral enamel/enameloid mineralization toolkit was based on Sparc-L, a situation maintained in holocephalans. The elasmobranch toolkit includes Sparc-L and Scpp, whereas Sparc-L1 and Sparc-L2 were functionally replaced by the Scpp family in osteichthyans.
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In bony vertebrates, skeletal mineralization relies on the secretory calcium-binding phosphoproteins (Scpp) family whose members are acidic extracellular proteins posttranslationally regulated by the Fam20°C kinase. As scpp genes are absent from the elephant shark genome, they are currently thought to be specific to bony fishes (osteichthyans). Her...
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... the maintenance of acidic residues and SxE sites in spite of significant sequence turnover); and (3) the regulatory level (i.e., the restriction of expression to the secretory ameloblasts). Scpp parallel evolution, therefore, represents a unique scenario that improves our understanding of independently evolved genes. Indeed, our proposed model ( fig. 5) differs from other cases of independently evolved proteins that have The specific expression of scpp in secretory ameloblasts during catshark tooth and scale development strongly suggests that the elasmobranch scpp is a functional gene involved in enameloid matrix secretion and/or maturation. This idea is further supported by the ...
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... et al. 2017) and in SxE sites (1.9 sites per 100 a.a. on average, data not shown). As a result, we conclude that, in the jawed vertebrate lineage, an acidic Sparc-L protein was ancestrally phosphorylated by Fam20°C and was also binding calcium during enameloid formation, a situation that probably already existed in osteostracans and placoderms ( fig. 5A), and that remained largely unchanged in the holocephalan lineage ( fig. 5B). Elasmobranchs and osteichthyans convergently evolved Scpp proteins that respectively function redundantly with Sparc-L ( fig. 5C) or eventually took over the role ancestrally played by Sparc-L1/L2 ( fig. ...
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... shown). As a result, we conclude that, in the jawed vertebrate lineage, an acidic Sparc-L protein was ancestrally phosphorylated by Fam20°C and was also binding calcium during enameloid formation, a situation that probably already existed in osteostracans and placoderms ( fig. 5A), and that remained largely unchanged in the holocephalan lineage ( fig. 5B). Elasmobranchs and osteichthyans convergently evolved Scpp proteins that respectively function redundantly with Sparc-L ( fig. 5C) or eventually took over the role ancestrally played by Sparc-L1/L2 ( fig. ...
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... Fam20°C and was also binding calcium during enameloid formation, a situation that probably already existed in osteostracans and placoderms ( fig. 5A), and that remained largely unchanged in the holocephalan lineage ( fig. 5B). Elasmobranchs and osteichthyans convergently evolved Scpp proteins that respectively function redundantly with Sparc-L ( fig. 5C) or eventually took over the role ancestrally played by Sparc-L1/L2 ( fig. ...
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... that probably already existed in osteostracans and placoderms ( fig. 5A), and that remained largely unchanged in the holocephalan lineage ( fig. 5B). Elasmobranchs and osteichthyans convergently evolved Scpp proteins that respectively function redundantly with Sparc-L ( fig. 5C) or eventually took over the role ancestrally played by Sparc-L1/L2 ( fig. ...
Citations
... Hatched boxes indicate genes found in only one of the two databases. earlier findings [21,22], including the debated convergent evolution of enamel-related genes [23,24] (Figure 2). We found that the presence of enamel-related SCPP genes correlated with the existence of teeth (Figure 1). ...
Genes within the secretory calcium-binding phosphoprotein (SCPP) family evolved in conjunction with major evolutionary milestones: the formation of a calcified skeleton in vertebrates, the emergence of tooth enamel in fish, and the introduction of lactation in mammals. The SCPP gene family also contains genes expressed primarily and abundantly in human saliva. Here, we explored the evolution of the saliva-related SCPP genes by harnessing currently available genomic and transcriptomic resources. Our findings provide insights into the expansion and diversification of SCPP genes, notably identifying previously undocumented convergent gene duplications. In primate genomes, we found additional duplication and diversification events that affected genes coding for proteins secreted in saliva. These saliva-related SCPP genes exhibit signatures of positive selection in the primate lineage while the other genes in the same locus remain conserved. We found that regulatory shifts and gene turnover events facilitated the accelerated gain of salivary expression. Collectively, our results position the SCPP gene family as a hotbed of evolutionary innovation, suggesting the potential role of dietary and pathogenic pressures in the adaptive diversification of the saliva composition in primates, including humans.
... Occlusion of dentinal tubules may be considered a protective mechanism in the absence of enameloid. The latter could indicate that in Anoplogaster cornuta inactivation of the matrix secretory calcium-binding phosphoprotein 5 (SCPP5) gene has occurred, which in actinopterygians regulate the formation of hypermineralized enameloid [28,29]. It would be interesting to analyze if this condition is already present in the teeth of larvae or if its occurrence is restricted to adult individuals. ...
We studied the structure and attachment modes of the teeth of adult Anoplogaster cornuta using light- and scanning-electron microscopic techniques. All teeth were monocuspid, composed solely of orthodentin, and lacked a covering enameloid cap. Fourteen teeth were present in the oral jaws, with three teeth each on the left and right premaxilla and four teeth each on the left and right dentary. The anteriormost premaxillary and dentary teeth were considerably larger than the more posteriorly located ones. The oral jaw teeth were transparent, non-depressible and firmly ankylosed to their respective dentigerous bone by a largely anosteocytic bone of attachment. No evidence for replacement of the large oral jaw teeth was found in the analyzed adult specimens. The bone of attachment exhibited lower calcium and phosphorus concentrations and a higher Ca/P ratio than the orthodentin. The connection between dentinal tooth shaft and bone of attachment was stabilized by a collar of mineralized collagen fibers. In contrast to the oral jaw teeth, the pharyngeal teeth exhibited a ring-like fibrous attachment to their supporting bones. This mode of attachment provides the teeth with some lateral mobility and allows their depression relative to their supporting bones, which may facilitate intra-pharyngeal prey transport. In contrast, a firm ankylosis was observed in numerous small teeth located on the branchial arches. The function of these teeth is presumably to increase the tightness of the pharyngeal basket and thereby the retention of small prey items in a species living in a habitat with only sparse food supply. Our findings corroborate earlier statements on the tooth attachment modes of the oral jaw teeth of Anoplogaster cornuta , but provide new findings for the attachment modes of pharyngeal teeth in this species.
Gars and bichirs develop scales and teeth with ancient actinopterygian characteristics. Their scale surface and tooth collar are covered with enamel, also known as ganoin, whereas the tooth cap is equipped with an enamel-like tissue, acrodin. Here, we investigated the formation and mineralization of the ganoin and acrodin matrices in spotted gar, and the evolution of the scpp5, ameloblastin (ambn), and enamelin (enam) genes, which encode matrix proteins of ganoin. Results suggest that, in bichirs and gars, all these genes retain structural characteristics of their orthologs in stem actinopterygians, presumably reflecting the presence of ganoin on scales and teeth. During scale formation, Scpp5 and Enam were initially found in the incipient ganoin matrix and the underlying collagen matrix, whereas Ambn was detected mostly in a surface region of the well-developed ganoin matrix. Although collagen is the principal acrodin matrix protein, Scpp5 was detected within the matrix. Similarities in timings of mineralization and the secretion of Scpp5 suggest that acrodin evolved by the loss of the matrix secretory stage of ganoin formation: dentin formation is immediately followed by the maturation stage. The late onset of Ambn secretion during ganoin formation implies that Ambn is not essential for mineral ribbon formation, the hallmark of the enamel matrix. Furthermore, Scpp5 resembles amelogenin that is not important for the initial formation of mineral ribbons in mammals. It is thus likely that the evolution of ENAM was vital to the origin of the unique mineralization process of the enamel matrix.
