Porcine Amelogenin is Expressed from the X and Y Chromosomes

Tooth Enamel and its Dynamic Protein Matrix

Tooth enamel is the outer covering of tooth crowns, the hardest material in the mammalian body, yet fracture resistant. The extremely high content of 95 wt% calcium phosphate in healthy adult teeth is achieved through mineralization of a proteinaceous matrix that changes in abundance and composition. Enamel-specific proteins and proteases are known to be critical for proper enamel formation. Recent proteomics analyses revealed many other proteins with their roles in enamel formation yet to be unraveled. Although the exact protein composition of healthy tooth enamel is still unknown, it is apparent that compromised enamel deviates in amount and composition of its organic material. Why these differences affect both the mineralization process before tooth eruption and the properties of erupted teeth will become apparent as proteomics protocols are adjusted to the variability between species, tooth size, sample size and ephemeral organic content of forming teeth. This review summarizes the current knowledge and published proteomics data of healthy and diseased tooth enamel, including advancements in forensic applications and disease models in animals. A summary and discussion of the status quo highlights how recent proteomics findings advance our understating of the complexity and temporal changes of extracellular matrix composition during tooth enamel formation.

Enamel matrix derivative: a review of cellular effects in vitro and a model of molecular arrangement and functioning

BACKGROUND

Enamel matrix derivative (EMD), the active component of Emdogain®, is a viable option in the treatment of periodontal disease owing to its ability to regenerate lost tissue. It is believed to mimic odontogenesis, though the details of its functioning remain the focus of current research.

OBJECTIVE

The aim of this article is to review all relevant literature reporting on the composition/characterization of EMD as well as the effects of EMD, and its components amelogenin and ameloblastin, on the behavior of various cell types in vitro. In this way, insight into the underlying mechanism of regeneration will be garnered and utilized to propose a model for the molecular arrangement and functioning of EMD.

METHODS

A review of in vitro studies of EMD, or components of EMD, was performed using key words "enamel matrix proteins" OR "EMD" OR "Emdogain" OR "amelogenin" OR "ameloblastin" OR "sheath proteins" AND "cells." Results of this analysis, together with current knowledge on the molecular composition of EMD and the structure and regulation of its components, are then used to present a model of EMD functioning.

RESULTS

Characterization of the molecular composition of EMD confirmed that amelogenin proteins, including their enzymatically cleaved and alternatively spliced fragments, dominate the protein complex (>90%). A small presence of ameloblastin has also been reported. Analysis of the effects of EMD indicated that gene expression, protein production, proliferation, and differentiation of various cell types are affected and often enhanced by EMD, particularly for periodontal ligament and osteoblastic cell types. EMD also stimulated angiogenesis. In contrast, EMD had a cytostatic effect on epithelial cells. Full-length amelogenin elicited similar effects to EMD, though to a lesser extent. Both the leucine-rich amelogenin peptide and the ameloblastin peptides demonstrated osteogenic effects. A model for molecular structure and functioning of EMD involving nanosphere formation, aggregation, and dissolution is presented.

CONCLUSIONS

EMD elicits a regenerative response in periodontal tissues that is only partly replicated by amelogenin or ameloblastin components. A synergistic effect among the various proteins and with the cells, as well as a temporal effect, may prove important aspects of the EMD response in vivo.

A gene catalogue of the euchromatic male-specific region of the horse Y chromosome: comparison with human and other mammals

Studies of the Y chromosome in primates, rodents and carnivores provide compelling evidence that the male specific region of Y (MSY) contains functional genes, many of which have specialized roles in spermatogenesis and male-fertility. Little similarity, however, has been found between the gene content and sequence of MSY in different species. This hinders the discovery of species-specific male fertility genes and limits our understanding about MSY evolution in mammals. Here, a detailed MSY gene catalogue was developed for the horse – an odd-toed ungulate. Using direct cDNA selection from horse testis, and sequence analysis of Y-specific BAC clones, 37 horse MSY genes/transcripts were identified. The genes were mapped to the MSY BAC contig map, characterized for copy number, analyzed for transcriptional profiles by RT-PCR, examined for the presence of ORFs, and compared to other mammalian orthologs. We demonstrate that the horse MSY harbors 20 X-degenerate genes with known orthologs in other eutherian species. The remaining 17 genes are acquired or novel and have so far been identified only in the horse or donkey Y chromosomes. Notably, 3 transcripts were found in the heterochromatic part of the Y. We show that despite substantial differences between the sequence, gene content and organization of horse and other mammalian Y chromosomes, the functions of MSY genes are predominantly related to testis and spermatogenesis. Altogether, 10 multicopy genes with testis-specific expression were identified in the horse MSY, and considered likely candidate genes for stallion fertility. The findings establish an important foundation for the study of Y-linked genetic factors governing fertility in stallions, and improve our knowledge about the evolutionary processes that have shaped Y chromosomes in different mammalian lineages.

Limited immune-modulating activity of porcine mesenchymal stromal cells abolishes their protective efficacy in acute kidney injury

We demonstrated previously that administration of mesenchymal stromal cells (MSCs) after renal ischemia/reperfusion injury (IRI) in rats protected renal function and hastened repair through complex paracrine mechanisms. Here we investigated kidney-protective actions of MSCs in a porcine IRI model that may have relevance to human acute kidney injury (AKI). Groups of female pigs with bilateral IRI were infused with autologous or male allogeneic MSCs. No acute or late complications were observed, but unexpectedly, MSC therapy also had no beneficial effects on kidney function and histology. In vitro, we demonstrated substantial functional and phenotypic overlaps between rodent, human, and porcine MSCs, all of which exhibited trilineage differentiation, characteristic antigen profiles, and secretion of renoprotective vascular endothelial growth factor (VEGF)-A and insulin-like growth factor-1 (IGF-1). However, in striking contrast to human MSCs, porcine MSCs failed to inhibit the mixed lymphocyte reaction (MLR) and induced robust production of proinflammatory interleukin-6 (IL-6). In summary, in contrast to rodent models, treatment of porcine IRI with MSCs was not kidney-protective. This, we conclude, is due to the fact that porcine MSCs exert inadequate immune-modulating effects, further demonstrating that successful therapy of IRI with MSCs critically depends on their anti-inflammatory actions. As a consequence, treatment of AKI with MSCs is not informative regarding the investigation of the underlying mechanisms in this large animal model. We expect, however, that the treatment of human IRI of the kidney with immune-modulating MSCs will be as effective as in rodent models.

Mmp-20 and Klk4 cleavage site preferences for amelogenin sequences

Mmp-20 and Klk4 are the two key enamel proteases. Can both enzymes process amelogenin to generate the major cleavage products that accumulate during the secretory stage of amelogenesis? We isolated Mmp-20 and Klk4 from developing pig teeth and used them to digest the tyrosine-rich amelogenin polypeptide (TRAP), the leucine-rich amelogenin protein (LRAP), and 5 fluorescence peptides. We characterized the digestion products by LC-MSMS, SDS-PAGE, and C18 RP-HPLC monitored with fluorescence and UV detectors. Mmp-20 cleaves amelogenin sequences after Pro(162), Ser(148), His(62), Ala(63), and Trp(45). These cleavages generate all of the major cleavage products that accumulate in porcine secretory-stage enamel: the 23-kDa, 20-kDa, 13-kDa, 11-kDa, and 6-kDa (TRAP) amelogenins. Mmp-20 cleaves LRAP after Pro(45) and Pro(40), producing the two LRAP products previously identified in tooth extracts. Among these key cleavage sites, Klk4 was able to cleave only after His(62). We propose that Mmp-20 alone processes amelogenin during the secretory stage.

Differences of the porcine amelogenin X and Y chromosome genes (AMELX and AMELY) and their application for sex determination in pigs

Molecular sexing in wild and domestic animals has becoming an important issue in several fields including reproduction. X and Y chromosome-specific sequence differences of the amelogenin genes (AMELX and AMELY) have been described in different mammalian species and used for sex determination. We studied the possibility to use sequence variability between the porcine AMELX and AMELY genes for sex determination in pigs. Sequence analysis of about 400 bp of intron 3 of the porcine amelogenin genes showed the presence of a 9-10 bp deletion in AMELY gene compared to AMELX sequences. Moreover, one single nucleotide polymorphism (SNP) was detected for the AMELY sequence. Four other SNPs and 1 bp insertion differentiated three AMELX haplotypes indicating an unexpected quite high nucleotide diversity for a chromosome X region. Two sex determination assays targeting the 9-10 bp difference between AMELX and AMELY were developed. Assessment of the accuracy of the amelogenin assays to correctly sex individuals was tested on 329 pigs belonging to different breeds/lines. All analysed animals were correctly sexed with the new designed amelogenin tests. No amplification was obtained in human, cattle, goat, sheep, and horse genomic DNA. These assays can be used for sex diagnosis of small amounts of genomic DNA (20 pg) obtained from different sources including embryo biopsies, hair, meat, and other biological specimens. Thus, apart from the application in the reproduction field, these tests can be useful in several other sectors including forensics, archaeozoology, meat production, and processing as well as for quality control in sample identification.

The exon 6ABC region of amelogenin mRNA contribute to increased levels of amelogenin mRNA through amelogenin protein-enhanced mRNA stabilization

We recently demonstrated that the reuptake of full-length amelogenin protein results in increased levels of amelogenin mRNA through enhanced mRNA stabilization (Xu, L., Harada, H., Tamaki, T. Y., Matsumoto, S., Tanaka, J., and Taniguchi, A. (2006) J. Biol. Chem. 281, 2257-2262). Here, we examined the molecular mechanism of enhanced amelogenin mRNA stabilization. To identify the cis-regulatory region within amelogenin mRNA, we tested various reporter systems using a deletion series of reporter plasmids. A deletion at exon 6ABC of amelogenin mRNA resulted in a 2.5-fold increase in the amelogenin mRNA expression level when compared with that of full-length mRNA, indicating that a cis-element exists in exon 6ABC of amelogenin mRNA. Furthermore, Northwestern analysis demonstrated that amelogenin protein binds directly to its mRNA in vitro, suggesting that amelogenin protein acts as a trans-acting protein that specifically binds to this cis-element. Moreover, recombinant mouse amelogenin protein extended the half-life of full-length amelogenin mRNA but did not significantly alter the half-life of exon 6ABC-deletion mutant mRNA. The splice products produced by deletion of exon 6ABC are known as leucine-rich amelogenin peptides and have signaling effects on cells. Our findings also suggest that the regulation of full-length amelogenin protein expression differs from the regulation of leucine-rich amelogenin peptide expression.

The Induction and Possible Subsequent Effect of Human Antibodies Against Porcine Enamel Matrix Derivative

BACKGROUND

The amino acid sequence of porcine amelogenin, the major component of enamel matrix derivative (EMD), is approximately 91% identical to that of its human counterpart. Whether porcine EMD (pEMD) can elicit neutralizing antibodies after the first surgery, thereby reducing the clinical effect of secondary surgery, has not been established.

METHODS

The sera of patients receiving periodontal surgery with or without pEMD were collected before and after surgery. The pEMD product was subjected to electrophoresis and transferred for a Western blot using the purified antibodies from patients as the primary antibodies. To clarify whether the antibodies in patients could inhibit the production of transforming growth factor-beta1 (TGF-beta1), we added different amounts of purified antibodies from pEMD patients (before versus after surgery) into the cell cultures of periodontal ligament fibroblasts. The conditioned media were then collected for an immunoassay of TGF-beta1.

RESULTS

The result of the Western blot demonstrated that human antibodies against pEMD were elicited 10 days after surgery. Using mass spectrometry, a non-specific band on the Western blot appeared to be porcine immunoglobulin G (IgG). The results of the immunoassay showed the antibodies from pEMD-treated patients did not hinder the subsequent production of TGF-beta1.

CONCLUSIONS

The pEMD product was contaminated with porcine IgG. The application of the product could induce antibodies against different isoforms of porcine amelogenin in humans. However, the increased antibodies did not hinder the production of TGF-beta1, one of the established in vitro functions of pEMD on periodontal ligament fibroblasts.

Characterization of a mouse amelogenin [A-4]/M59 cell surface receptor

Amelogenin proteins comprise up to 90% of the organic matrix of developing enamel in the vertebrate tooth. Alternative splicing of mouse amelogenin pre-mRNA leads to the production of more than 14 protein isoforms, the functions of which are not totally understood. The smaller splice products, [A + 4] or M73 and [A - 4] or M59, have been shown to act differently as signaling molecules affecting odontogenic and other cell types. The mechanisms of these signaling processes, beginning with receptor identification, are not well understood. Utilizing radiolabeled [A - 4], we show here that 3H[A - 4] binds in a saturable fashion to the cell surface of C2C12 mouse fetal myoblasts at 4 degrees C, and not only binds at the surface but is internalized at 37 degrees C. "Far Western" immunohistochemistry performed on sections of E18 mouse incisors and molars with biotin-labeled [A - 4] as the primary ligand demonstrates [A - 4]-biotin binding to polarizing ameloblasts and odontoblasts, cells of the dental follicle, and along the stratum intermedium. Using [A - 4] affinity column chromatography and [A - 4]-biotin label transfer reaction, we have identified a 95 kDa C2C12 cell surface protein which bound [A - 4]. Utilizing Tandem MS (MS/MS) sequencing, we report the novel finding of the 95 kDa murine transmembrane protein, LAMP-1, originally identified as a lysosomal membrane protein that is also found at the cell surface, as an [A - 4] cell binding protein.