Expression of BSP-GFPtpz Transgene during Osteogenesis and Reparative Dentinogenesis

Bone sialoprotein (BSP) is a member of the SIBLING family with essential roles in skeletogenesis. In the developing teeth, although the expression and function of BSP in the formation of acellular cementum and periodontal attachment are well documented, there are uncertainties regarding the expression and function of BSP by odontoblasts and dentin. Reporter mice are valuable animal models for biological research, providing a gene expression readout that can contribute to cellular characterization within the context of a developmental process. In the present study, we examined the expression of a BSP-GFPtpz reporter mouse line during odontoblast differentiation, reparative dentinogenesis, and bone. In the developing teeth, BSP-GFPtpz was expressed at high levels in cementoblasts but not in odontoblasts or dentin. In bones, the transgene was highly expressed in osteoblasts at an early stage of differentiation. Interestingly, despite its lack of expression in odontoblasts and dental pulp during tooth development, the BSP-GFPtpz transgene was detected during in vitro mineralization of primary pulp cultures and during reparative dentinogenesis following pulp exposures. Importantly, under these experimental contexts, the expression of BSP-GFPtpz was still exclusive to DSPP-Cerulean, an odontoblast-specific reporter gene. This suggests that the combinatorial use of BSP-GFPtpz and DSPP-Cerulean can be a valuable experimental tool to distinguish osteogenic from dentinogenic cells, thereby providing an avenue to investigate mechanisms that distinctly regulate the lineage progression of progenitors into odontoblasts versus osteoblasts.

FGF Signaling Prevents the Terminal Differentiation of Odontoblasts

Members of the fibroblast growth factor (FGF) family play essential and important roles in primary and reparative dentinogenesis, with conflicting results regarding their effects on odontoblast differentiation. Our recent studies showed that the effects of FGF2 on cells in odontoblast lineage were stage-specific and depended on the stage of cell maturity. Continuous exposure of pulp cells to FGF2 inhibited odontoblast differentiation, whereas early and limited exposure of pulp cells to FGF2 resulted in marked increases in odontoblast differentiation. The purpose of this study was to evaluate the cellular and molecular mechanisms regulating the inhibitory effects of FGF2 on odontoblast differentiation. To do so, we examined the effects of the addition of FGF2 during the differentiation/mineralization phase of the in vitro growth of pulp cultures derived from a series of green fluorescent protein reporter transgenic mice that display stage-specific activation of transgenes during odontoblast differentiation. Our results showed that this treatment first stimulated the differentiation of remaining progenitors in pulp cultures into functional odontoblasts but prevented their differentiation into mature odontoblasts. In addition, this treatment inhibited expression of markers of osteogenesis. Furthermore, we demonstrated that the inhibitory effects of FGF2 on odontoblast differentiation were mediated through activation of FGFR/MEK/Erk1/2 signaling and downregulation of bone morphogenetic protein signaling, with negative and positive roles in the expression of Dmp1 and Dspp, respectively, during the advanced stage of odontoblast differentiation.

Enhanced Dentinogenesis of Pulp Progenitors by Early Exposure to FGF2

Members of the fibroblast growth factor (FGF) family play essential and important roles in primary and reparative dentinogenesis. Although there appears to be a general agreement on the effects of FGF signaling on the proliferation of pulp cells, there are conflicting results regarding its effects on odontoblast differentiation. We recently examined the effects of continuous exposure of dental pulp cells to FGF2 and showed that the effects of FGF2 on differentiation of progenitor cells into odontoblasts were stage specific and dependent on the stage of cell maturity. The purpose of this study was to gain further insight into cellular and molecular mechanisms regulating the stimulatory effects of FGF2 on odontoblast differentiation. To do so, we examined the effects of early and limited exposure of pulp cells from a series of green fluorescent protein (GFP) reporter transgenic mice that display stage-specific activation of transgenes during odontoblast differentiation to FGF2. Our results showed that early and limited exposure of pulp cells to FGF2 did not have significant effects on the extent of mineralization but induced significant increases in the expression of Dmp1 and Dspp and the number of DMP1-GFP(+) and DSPP-Cerulean(+) odontoblasts. Our results also showed that the stimulatory effects of FGF2 on odontoblast differentiation were mediated through FGFR/MEK/Erk1/2 signaling, increases in Bmp2, and activation of the BMP/BMPR signaling pathway. These observations show that early and limited exposure of pulp cells to FGF2 alone promotes odontoblast differentiation and provides critical insight for applications of FGF2 in dentin regeneration.

Indian hedgehog signaling in extraembryonic endoderm and ectoderm differentiation in ES embryoid bodies

We previously demonstrated that a member of the Hedgehog gene family, Indian hedgehog (Ihh), is expressed in the visceral endoderm of EC and ES cell embryoid bodies and mouse embryos. Overexpression studies suggested that Ihh was involved in visceral endoderm differentiation. We now provide evidence for a Hh response in the embryoid body core and in the mesothelial layer of the visceral yolk sac. We also demonstrate that treatment of ES embryoid bodies with the Hh antagonists cAMP and forskolin results in downregulation of the Hh response and altered embryoid body differentiation. The outer endoderm layer undergoes a transition to parietal endoderm while formation of an embryonic ectoderm layer surrounding a cavity is inhibited. These treatments also result in a decrease in the expression of markers for the mesoderm derivatives, blood and endothelial cells. We present a model to explain how Ihh and BMP signaling may regulate extraembryonic endoderm and embryonic ectoderm differentiation.

Using EC and ES cell culture to study early development: recent observations on Indian hedgehog and Bmps

Despite great technological advances in the study of mammalian development in the past two decades, certain problems in early development, such as how the extraembryonic lineages are established, have remained intractable. We suggest that teratocarcinoma (EC) and embryonic stem cells (ES) remain useful in vitro tools for studying some of these problems. We present a continuation of our studies on the role of IHH-based signaling in early development and demonstrate that the IHH N-peptide is expressed in the outer visceral endoderm cells of both the EC and ES-derived embryoid body. We also show that Bmp2 is upregulated and Bmp4 downregulated during the differentiation of F9 EC cells into embryoid bodies, whereas both genes are upregulated when J7 ES cells differentiate into embryoid bodies. We also examine the spatial localization of Ihh, Bmp2, and Bmp4 in day 6.5-7.0 and 7.5-8.0 embryos by in situ hybridization analysis. These data support the EC temporal expression data in that all 3 genes are expressed in visceral endoderm. Bmp4 expression appears to be limited to extraembryonic regions, where mesoderm as well as visceral endoderm are stained. Ihh and Bmp2 are expressed in extraembryonic tissues and the embryo proper. Functional roles for the observed expression patterns are discussed.

Nucleotide sequences of MHC class I introns 1, 2, and 3 in humans and intron 2 in nonhuman primates

HLA-class I genes are the most polymorphic genetic system yet known. The polymorphic substitutions are mostly located in exon 2 and 3, encoding alpha 1 and alpha 2 domains, respectively, which are involved in peptide binding and T cell receptor interaction. In this study, we present the sequences of the introns neighboring the polymorphic exons in humans with few examples from nonhuman primates. In general, intron sequences are found to be less polymorphic than the adjacent exons, displaying numerous locus-specific and group-specific sites. These sequences will provide important information for developing DNA based typing strategies for HLA-class I alleles.

Locus-specific amplification of HLA class I genes from genomic DNA: locus-specific sequences in the first and third introns of HLA-A, -B, and -C alleles

We have identified locus-specific sequences in the first and third introns flanking the polymorphic second and third exons of HLA class I genes. PCR primers derived from these conserved sequences produced DNA fragments of the expected sizes for each of the HLA-A, -B, and -C loci in the amplification of genomic DNA. PCR products generated using each of the locus-specific sets of primers displayed exquisite locus specificity, as assessed by hybridization with oligonucleotide probes specific for ten classical and non-classical HLA class I genes. Amplification with these primer sets was effective and specific for the HLA alleles tested under the given PCR conditions. When hybridized with oligonucleotides derived from shared polymorphic sequence motifs, reaction patterns of PCR products from each locus were precisely as expected from published or database sequences. Chemiluminescent signals generated from digoxygenin-ddUTP-labeled probes were even for all samples and as strong as those obtained in MHC class II typing. These locus-specific primer sets derived from intron sequences provide an effective means to amplify genomic DNA which will facilitate PCR-based HLA class I typing methods. This will also allow HLA class I typing to be conducted with greater precision, at lower cost, and faster than previously described class I typing methodologies.

Nonrandom allelic variation in the regulatory complex of HLA class I genes

Recently, we have demonstrated that the HLA class I regulatory complex (CRC) is conserved in a locus-specific manner with limited allelic variation. In this study, we have analyzed the CRC sequences of the alleles that showed variation from a total of 22 well-characterized, HLA-homozygous B-LCLs, using PCR amplification of genomic DNA and direct sequencing. We compared the sequences of these alleles with their respective locus consensus sequence at kappa B1, kappa B2, the IRS, the putative NRE, and the HLA counterpart of the H-2RII region, the R x R beta-binding site. The palindromic kappa B1 sequence, an active enhancer, was found to be conserved in all HLA-A and -B alleles and in one HLA-C allele. The sequences of the kappa B2 site showed locus-specific divergence with almost no allelic variation. The IRS is strictly locus specific and HLA-B and -C have identical sequences in this region. Variation in the putative NRE sequence and RII-kappa B2 junctional sequence was apparently generated by gene conversion between B and C loci. Each locus had two sequence patterns at the putative RII site. Overall, sequence analysis of variant alleles demonstrated that there is limited variation in a nonrandom fashion. These results may provide a structural basis for locus and allele-specific modulation of these genes.

Hyperprealbuminemia, euthyroid hyperthyroxinemia, Zollinger-Ellison-like syndrome and hypercorticism in a pancreatic endocrine tumour

Prealbumin, one of the main thyroxine transport proteins, has recently been shown to be a valuable immunohistochemical marker of neuroendocrine tumours. We report the case of a multisecretory pancreatic endocrine tumour whose prealbumin secretion was so high that it produced a peak on routine serum protein electrophoresis and induced a euthyroid hyperthyroxinemia. The maximal binding capacity of prealbumin for thyroxine was indeed markedly increased, whereas its affinity for this hormone was normal. The tumour was associated with gastric hyperacidity and hypergastrinemia thereby evoking a Zollinger-Ellison syndrome. The secretin stimulation test and gastrin tumoural immunohistochemistry were, however, negative. We suggest that the concomitant tumoural production of gastrin-releasing peptide was responsible for the gastric hyperacidity and hypergastrinemia. This hormone probably also accounted for a moderate hypercorticism.