Laminin alpha5 is required for dental epithelium growth and polarity and the development of tooth bud and shape

LAMA5: A new pathogenic gene for non-syndromic cleft lip with or without cleft palate

BACKGROUND

This study aimed to investigate the effect of LAMA5 on palatal development in mice.

METHODS

The palatine process of C57BL/6 J fetal mice on the embryonic day 13.5 (E13.5) was cultured in vitro via the rotating culture method. The LAMA5-shRNA adenovirus vector was constructed, then transfected into the palatal process of E13.5 for 48 h in vitro. A fluorescence microscope was used to visualize the fusion of palates. The expression of LAMA5 was also detected. The expression of ki67, cyclin D1, caspase 3, E-cadherin, vimentin and SHH signaling pathway-related signaling factors in the blank control group, the negative control group, and the LAMA5 interference group were detected after virus transfection.

RESULTS

The bilateral palates in the LAMA5 interference group were not fused after virus transfection. PCR and WB showed that the mRNA and protein expressions of LAMA5 were decreased in the LAMA5 interference group. Furthermore, the mRNA and protein expressions of ki67, cyclin D1 and gli1 were decreased in the LAMA5 interference group, while the mRNA and protein expressions of caspase 3 were increased. However, the mRNA and protein expression of E-cadherin, vimentin, Shh and ptch1 did not significantly change in the LAMA5 interference group.

CONCLUSIONS

LAMA5 silencing causes cleft palate by inhibiting the proliferation of mouse palatal cells and promoting apoptosis, which may not be involved in EMT. LAMA5 silencing can also cause cleft palate by interfering with the SHH signaling pathway.

LAMA5-inspired adhesive dodecapeptide facilitates efficient dentine regeneration: An in vitro and in vivo study

AIM

The primary goal of this study was to investigate the potential effects of A5G81 in inducing reparative dentine (RD) formation both in vitro and in vivo.

METHODOLOGY

Cell adhesion was observed by crystal violet staining and quantified by Sodium Dodecyl Sulphate (SDS) extraction. Cell proliferation was investigated using Cell Counting Kit-8 (CCK-8) assay. Spreading of cytoskeleton was visualized using immunofluorescence staining. Protein expression level of Akt signalling pathway was compared in a human Akt pathway phosphorylation array. Genes that were up or downregulated by A5G81 were identified by RNA sequencing. The mRNA expression of odontoblastic markers was detected by quantitative real-time polymerase chain reaction (qPCR). Moreover, mineralization of human dental pulp cells (hDPCs) was visualized by alizarin red staining and quantified using cetylpyridinium chloride (CPC). A direct pulp-capping model was established in SD rats and the RD formation at 2 weeks after operation was observed using HE staining.

RESULTS

A5G81 (optimal coating concentration: 0.5 mg/mL) promoted hDPCs adhesion and proliferation to a level that was similar to Type I collagen (COL-1). Meanwhile, A5G81 activated Akt signalling pathway, albeit to a lesser extent than COL-1. An inhibition test indicated that A5G81 induced hDPCs adhesion by activating PI3K pathway. A5G81 induced the expression of ECM remodelling genes and odontoblastic genes, which were demonstrated by RNA-seq and qPCR, respectively. In addition, A5G81 efficiently accelerated the mineralization of hDPCs in both immobilized and soluble forms, a property that makes it more applicable in dental clinic. Finally, the pulp-capping study in rats suggested that use of A5G81 could successfully induce the formation of RD within 2 weeks.

CONCLUSION

Coating of A5G81 to non-tissue culture-treated polystyrene facilitates spreading, proliferation and differentiation of hDPCs, resulting in rapid RD formation in artificially exposed pulp.

MEMO1 Is Required for Ameloblast Maturation and Functional Enamel Formation

Coordinated mineralization of soft tissue is central to organismal form and function, while dysregulated mineralization underlies several human pathologies. Oral epithelial-derived ameloblasts are polarized, secretory cells responsible for generating enamel, the most mineralized substance in the human body. Defects in ameloblast development result in enamel anomalies, including amelogenesis imperfecta. Identifying proteins critical in ameloblast development can provide insight into specific pathologies associated with enamel-related disorders or, more broadly, mechanisms of mineralization. Previous studies identified a role for MEMO1 in bone mineralization; however, whether MEMO1 functions in the generation of additional mineralized structures remains unknown. Here, we identify a critical role for MEMO1 in enamel mineralization. First, we show that Memo1 is expressed in ameloblasts and, second, that its conditional deletion from ameloblasts results in enamel defects, characterized by a decline in mineral density and tooth integrity. Histology revealed that the mineralization defects in Memo1 mutant ameloblasts correlated with a disruption in ameloblast morphology. Finally, molecular profiling of ameloblasts and their progenitors in Memo1 oral epithelial mutants revealed a disruption to cytoskeletal-associated genes and a reduction in late-stage ameloblast markers, relative to controls. Collectively, our findings integrate MEMO1 into an emerging network of molecules important for ameloblast development and provide a system to further interrogate the relationship of cytoskeletal and amelogenesis-related defects.

Identification of potential key variants in mandibular premolar hypodontia through whole-exome sequencing

Determining genotype-phenotype correlations in patients with hypodontia is important for understanding disease pathogenesis, although only a few studies have elucidated it. We aimed to identify genetic variants linked to non-syndromic bilateral mandibular second premolar hypodontia in a Korean population for the first time by specifying the phenotype of hypodontia. Twenty unrelated individuals with non-syndromic bilateral mandibular second premolar hypodontia were enrolled for whole-exome sequencing. Using a tooth agenesis gene set panel consisting of 112 genes based on literature, potential candidate variants were screened through variant filtering and prioritization. We identified 13 candidate variants in 12 genes, including a stop-gain variant (c.4750C>T) in LAMA3. Through the functional enrichment analysis of the prioritized genes, several terms related to tooth development were enriched in a protein-protein interaction network of candidate genes for mandibular premolar hypodontia. The hypodontia group also had approximately 2-fold as many mutated variants in all four genes related to these key terms, which are CDH1, ITGB4, LAMA3, LAMB3, as those in the 100 healthy control group individuals. The relationship between enriched terms and pathways and mandibular premolar hypodontia was also investigated. In addition, we identified some known oligodontia variants in patients with hypodontia, strengthening the possibility of synergistic effects in other genes. This genetic investigation may be a worthwhile preliminary attempt to reveal the pathogenesis of tooth agenesis and sets a background for future studies.

Characterizing Intraindividual Podocyte Morphology In Vitro with Different Innovative Microscopic and Spectroscopic Techniques

Podocytes are critical components of the glomerular filtration barrier, sitting on the outside of the glomerular basement membrane. Primary and secondary foot processes are characteristic for podocytes, but cell processes that develop in culture were not studied much in the past. Moreover, protocols for diverse visualization methods mostly can only be used for one technique, due to differences in fixation, drying and handling. However, we detected by single-cell RNA sequencing (scRNAseq) analysis that cells reveal high variability in genes involved in cell type-specific morphology, even within one cell culture dish, highlighting the need for a compatible protocol that allows measuring the same cell with different methods. Here, we developed a new serial and correlative approach by using a combination of a wide variety of microscopic and spectroscopic techniques in the same cell for a better understanding of podocyte morphology. In detail, the protocol allowed for the sequential analysis of identical cells with light microscopy (LM), Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Skipping the fixation and drying process, the protocol was also compatible with scanning ion-conductance microscopy (SICM), allowing the determination of podocyte surface topography of nanometer-range in living cells. With the help of nanoGPS Oxyo^®, tracking concordant regions of interest of untreated podocytes and podocytes stressed with TGF-β were analyzed with LM, SEM, Raman spectroscopy, AFM and SICM, and revealed significant morphological alterations, including retraction of podocyte process, changes in cell surface morphology and loss of cell-cell contacts, as well as variations in lipid and protein content in TGF-β treated cells. The combination of these consecutive techniques on the same cells provides a comprehensive understanding of podocyte morphology. Additionally, the results can also be used to train automated intelligence networks to predict various outcomes related to podocyte injury in the future.

Using whole exome sequencing to identify susceptibility genes associated with nonsyndromic cleft lip with or without cleft palate

Cleft lip and palate is a common congenital birth defect in humans. Its incidence rate in China is as high as 1.82%, and is now a frequent deformity observed among the Chinese population; moreover, it varies across regions. Although the etiology of nonsyndromic cleft lip with or without cleft palate (NSCL/P) has been widely investigated, the results are inconsistent. The specific genes and mechanisms responsible for NSCL/P have not been fully understood. Whole exome sequencing (WES) is a new strategy for studying pathogenic genes. WES studies on NSCL/P have not been conducted in East China. Therefore, the aim of this study was to screen candidate genes of NSCL/P in East China using WES and analyze the temporal and spatial expressions of the candidate genes during embryonic palatal development. WES was performed in 30 children with NSCL/P from East China to screen candidate genes. A bioinformatics analysis was performed using commercially available software. Variants detected by WES were validated by immunohistochemistry and western blotting. After WES, 506,144 single-nucleotide variant sites were found. The results of database comparison, functional analysis, and mass spectrometry revealed that only the laminin alpha 5 (LAMA5) gene (site: rs145192286) was associated with NSCL/P. Immunohistochemistry results showed that LAMA5 expression in the medial edge epithelium changed with formation, lifting, and contact during palatogenesis. Almost no LAMA5 expression was detected in the palatal mesenchyme or after palatal fusion. Western blotting and immunohistochemistry results showed consistent trends. In conclusion, the WES results shows that the mutation at the site (rs145192286) of LAMA5 is associated with NSCL/P. The temporal and spatial expressions of LAMA5 during palatal development further demonstrate the involvement of this gene. Therefore, we speculate that LAMA5 is a new candidate pathogenic gene of NSCL/P. The identification of new pathogenic genes would help elucidate the pathogenesis of NSCL/P and provide a scientific basis for the prenatal diagnosis, prevention, and treatment of NSCL/P.

Functional Diversification of SRSF Protein Kinase to Control Ubiquitin-Dependent Neurodevelopmental Signaling

Conserved protein kinases with core cellular functions have been frequently redeployed during metazoan evolution to regulate specialized developmental processes. The Ser/Arg (SR)-rich splicing factor (SRSF) protein kinase (SRPK), which is implicated in splicing regulation, is one such conserved eukaryotic kinase. Surprisingly, we show that SRPK has acquired the capacity to control a neurodevelopmental ubiquitin signaling pathway. In mammalian embryonic stem cells and cultured neurons, SRPK phosphorylates Ser-Arg motifs in RNF12/RLIM, a key developmental E3 ubiquitin ligase that is mutated in an intellectual disability syndrome. Processive phosphorylation by SRPK stimulates RNF12-dependent ubiquitylation of nuclear transcription factor substrates, thereby acting to restrain a neural gene expression program that is aberrantly expressed in intellectual disability. SRPK family genes are also mutated in intellectual disability disorders, and patient-derived SRPK point mutations impair RNF12 phosphorylation. Our data reveal unappreciated functional diversification of SRPK to regulate ubiquitin signaling that ensures correct regulation of neurodevelopmental gene expression.

Transcriptional Regulation of Dental Epithelial Cell Fate

Dental enamel is hardest tissue in the body and is produced by dental epithelial cells residing in the tooth. Their cell fates are tightly controlled by transcriptional programs that are facilitated by fate determining transcription factors and chromatin regulators. Understanding the transcriptional program controlling dental cell fate is critical for our efforts to build and repair teeth. In this review, we describe the current understanding of these regulators essential for regeneration of dental epithelial stem cells and progeny, which are identified through transgenic mouse models. We first describe the development and morphogenesis of mouse dental epithelium in which different subpopulations of epithelia such as ameloblasts contribute to enamel formation. Then, we describe the function of critical factors in stem cells or progeny to drive enamel lineages. We also show that gene mutations of these factors are associated with dental anomalies in craniofacial diseases in humans. We also describe the function of the master regulators to govern dental lineages, in which the genetic removal of each factor switches dental cell fate to that generating hair. The distinct and related mechanisms responsible for the lineage plasticity are discussed. This knowledge will lead us to develop a potential tool for bioengineering new teeth.

Mouse Embryonic Tooth Germ Dissection and Ex vivo Culture Protocol

A tooth germ ex vivo organ culture allows visualization of its development in different stages, thus enabling investigation of the molecular mechanisms of regulatory factors. Tooth germs can be rapidly dissected from E13 mouse embryos and placed on cell culture inserts for observation of subsequent tooth germ development in a three-dimensional situation in real time. This method is also suitable for other organs that develop by epithelial-mesenchymal interactions, including salivary gland, hair, lung, and kidney. In addition, siRNAs or growth factors can be easily added to ex vivo tooth germ cultures to investigate the detailed molecular function of specific genes. The present protocol provides an efficient and practical method for isolation and ex vivo culture of embryonic tooth germs.

Laminin α5 modulates fibroblast proliferation in epidural fibrosis through the PI3K/AKT/mTOR signaling pathway

Lumbar laminectomy is commonly deemed as the most valid surgery for a series of lumbar illnesses, such as lumbar disc herniation, which could lead to spinal canal stenosis. However, epidural fibrosis is one of the most common complications that limits the application of lumbar laminectomy, which is mainly caused by proliferation of local fibroblasts. Laminins are glycoproteins that consist of α, β and γ chains, which serve a crucial role in biological cell behaviors, such as adhesion, differentiation, migration and proliferation, especially the isoform with the fifth α chain-laminin α5. The PI3K/AKT/mTOR signaling pathway was demonstrated to be associated with various biological functions in cells. The aim of the present study was to explore whether laminin α5 is an important factor in epidural fibrosis by modulating the proliferation of fibroblasts through the activation of PI3K/AKT/mTOR signaling pathway. In the animal model, the results of the hematoxylin-eosin staining, cell counting, Masson's trichrome staining and immunohistochemical staining showed laminin α5 to be positively associated with epidural fibrosis. Furthermore, to verify the assumption that laminin α5 could modulate fibroblast proliferation through the PI3K/AKT/mTOR signal pathway, fibroblasts were transfected with laminin α5-small interfering (si)RNA. The results of western blotting (proliferating cell nuclear antigen and cyclin D1), the Cell Counting Kit-8 and EdU incorporation assays indicated that the proliferative level of fibroblasts decreased, and the expression of phosphorylated (p)-focal adhesion kinase 1, p-AKT and p-mTOR was reduced. Subsequently, laminin α5 was overexpressed and the change in cell proliferation and expression of associated proteins contrasted with that observed in siRNA. The results demonstrated that laminin α5 could interfere the activation of the PI3K/AKT/mTOR signaling pathway. Finally, the inhibition of the PI3K/AKT/mTOR signaling pathway by LY294002 resulted in decreased fibroblast proliferation. In conclusion, laminin α5 could modulate fibroblast proliferation in epidural fibrosis through the PI3K/AKT/mTOR signaling pathway.

Sox2 maintains epithelial cell proliferation in the successional dental lamina

OBJECTIVES

The successional dental lamina is the distinctive structure on the lingual side of the vertebrate tooth germ. The aim of this study was to investigate the relationship among Sox2, Claudin10 and laminin5 and the role of Sox2 in successional dental lamina proliferation during vertebrate tooth development.

MATERIALS AND METHODS

To understand the successional dental lamina, two types of successional tooth formation, that in geckos (with multiple rounds of tooth generation) and that in mice (with only one round of tooth generation), were analysed.

RESULTS

Unique coexpression patterns of Sox2 and Claudin10 expression were compared in the successional dental lamina from the cap stage to the late bell stage in the mouse tooth germ and in juvenile gecko teeth to support continuous tooth replacement. Furthermore, Laminin5 expression was shown in the cap stage and decreased after the bell stage. Upon comparing the epithelial cell cycles and cell proliferation in successional dental lamina regions between mouse and gecko molars using BrdU and IdU staining and pulse-chase methods, distinctive patterns of continuous expression were revealed. Moreover, Sox2 overexpression with a lentiviral system resulted in hyperplastic dental epithelium in mouse molars.

CONCLUSIONS

Our findings indicate that the regulation of Sox2 in dental lamina proliferation is fundamental to the successional dental lamina in both species.

[Polarity of ameloblasts and odontoblasts and their related regulators]

The polarity of ameloblasts and odontoblasts is crucial for their differentiation and function. Polarity-related molecules play an important role in this process. This review summarizes the process of polarity formation of ameloblasts and odontoblasts and their related regulators.

Visualization of junctional epithelial cell replacement by oral gingival epithelial cells over a life time and after gingivectomy

Junctional epithelium (JE), which is derived from odontogenic epithelial cells immediately after eruption, is believed to be gradually replaced by oral gingival epithelium (OGE) over a lifetime. However, the detailed process of replacement remains unclear. The aim of the present study was to clarify the process of JE replacement by OGE cells using a green fluorescent protein (GFP)–positive tooth germ transplantation method. GFP-positive JE was partly replaced by OGE cells and completely replaced on day 200 after transplantation, whereas there was no difference in the expression of integrin β4 (Itgb4) and laminin 5 (Lama5) between JE before and after replacement by OGE cells. Next, GFP-positive JE was partially resected. On day 14 after resection, the regenerated JE consisted of GFP-negative cells and also expressed both Itgb4 and Lama5. In addition, the gene expression profile of JE derived from odontogenic epithelium before gingivectomy was partly different from that of JE derived from OGE after gingivectomy. These results suggest that JE derived from the odontogenic epithelium is gradually replaced by OGE cells over time and JE derived from the odontogenic epithelium might have specific characteristics different to those of JE derived from OGE.

iMatrix-511 Stimulates the Proliferation and Differentiation of MDPC-23 Cells into Odontoblastlike Phenotype

INTRODUCTION

iMatrix-511 is a novel integrin-binding fragment derived from laminin-511. Previous studies showed its superiority as a culture substrate for xeno-free culture and maintenance of pluripotency in stem cells. However, its effects in the dental field remain largely unknown. The aim of the present study was to unravel the in vitro effects of iMatrix-511 in comparison with vitronectin (VN).

METHODS

Biochemical assays were performed in vitro in MDPC-23 cells. The optimal coating density for 2 proteins was determined using the cell counting kit-8. To evaluate cell proliferation to both proteins, MDPC-23 cells were directly seeded onto the iMatrix-511 or VN-modified polystyrene and analyzed by the cell counting kit-8. The phenotype of cells seeded on iMatrix-511 and VN was characterized. Phenotypic characterization included real-time reverse-transcription polymerase chain reaction and alizarin red staining.

RESULTS

The optimal coating density for iMatrix-511 and VN was determined to be 1 μg/cm² and 0.25 μg/cm², respectively. Cells cultured on iMatrix-511 showed higher cell proliferative activity than the noncoated control and VN on days 1, 2, and 4. Cell morphology observation revealed MDPC-23 cells attach preferentially to iMatrix-511 and start to spread as early as 1 hour after inoculation. MDPC-23 cells exhibited more potent odontogenic differentiation on iMatrix-511 than the control and VN as shown by the marked enhancement of dentin matrix protein 1 and dentin sialophosphoprotein messenger RNA expression. Although both proteins showed more mineralized nodule formation than the control, iMatrix-511 remained to be the one that elicited stronger calcific deposition.

CONCLUSIONS

iMatrix-511 supported the proliferation and acquisition of odontogenic cell phenotype in vitro, rendering this novel material a potential candidate for dentin regeneration.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

Nephronectin plays critical roles in Sox2 expression and proliferation in dental epithelial stem cells via EGF-like repeat domains

Tooth development is initiated by epithelial-mesenchymal interactions via basement membrane (BM) and growth factors. In the present study, we found that nephronectin (Npnt), a component of the BM, is highly expressed in the developing tooth. Npnt localizes in the BM on the buccal side of the tooth germ and shows an expression pattern opposite that of the dental epithelial stem cell marker Sox2. To identify the roles of Npnt during tooth development, we performed knockdown and overexpression experiments using ex vivo organ and dental epithelial cell cultures. Our findings showed that loss of Npnt induced ectopic Sox2-positive cells and reduced tooth germ size. Over expression of Npnt showed increased proliferation, whereas the number of Sox2-positive cells was decreased in dental epithelial cells. Npnt contains 5 EGF-like repeat domains, as well as an RGD sequence and MAM domain. We found that the EGF-like repeats are critical for Sox2 expression and cell proliferation. Furthermore, Npnt activated the EGF receptor (EGFR) via the EGF-like repeat domains and induced the PI3K-Akt signaling pathway. Our results indicate that Npnt plays a critical scaffold role in dental epithelial stem cell differentiation and proliferation, and regulates Sox2 expression during tooth development.

Laminin: loss-of-function studies

Laminin, one of the most widely expressed extracellular matrix proteins, exerts many important functions in multiple organs/systems and at various developmental stages. Although its critical roles in embryonic development have been demonstrated, laminin's functions at later stages remain largely unknown, mainly due to its intrinsic complexity and lack of research tools (most laminin mutants are embryonic lethal). With the advance of genetic and molecular techniques, many new laminin mutants have been generated recently. These new mutants usually have a longer lifespan and show previously unidentified phenotypes. Not only do these studies suggest novel functions of laminin, but also they provide invaluable animal models that allow investigation of laminin's functions at late stages. Here, I first briefly introduce the nomenclature, structure, and biochemistry of laminin in general. Next, all the loss-of-function mutants/models for each laminin chain are discussed and their phenotypes compared. I hope to provide a comprehensive review on laminin functions and its loss-of-function models, which could serve as a reference for future research in this understudied field.

Involvement of PI3K and PKA pathways in mouse tongue epithelial differentiation

In mice, tongue epithelial differentiation is mainly regulated by the interactions among various signalling molecules including Fgf signalling pathways. However, the subsequent signalling modulations for epithelial maturation, initiated by Fgf signalling, remain to be elucidated. Therefore, we employed an in vitro tongue organ cultivation system along with the applications of various pharmacological inhibitors against the intracellular signalling molecules of Fgf signalling pathways, including H89, LY294002, PD98059, and U0126. Following treatments with LY294002 and H89, inhibitors for PI3K and PKA, respectively, the decreased thickness of the tongue epithelium was observed along with the alteration in cell proliferative and apoptotic patterns. Meanwhile, cultivated tongues treated with MEK inhibitor U0126 or PD98059 showed significantly decreased cell proliferation in the tongue epithelium and the mesenchyme. Based on these results, we suggest that the tongue epithelium is differentiated into multiple epithelial cell layers via the PI3K and PKA pathways in tissue-specific manner during the epithelial-mesenchymal interactions.

Globoside accelerates the differentiation of dental epithelial cells into ameloblasts

Tooth crown morphogenesis is tightly regulated by the proliferation and differentiation of dental epithelial cells. Globoside (Gb4), a globo-series glycosphingolipid, is highly expressed during embryogenesis as well as organogenesis, including tooth development. We previously reported that Gb4 is dominantly expressed in the neutral lipid fraction of dental epithelial cells. However, because its functional role in tooth development remains unknown, we investigated the involvement of Gb4 in dental epithelial cell differentiation. The expression of Gb4 was detected in ameloblasts of postnatal mouse molars and incisors. A cell culture analysis using HAT-7 cells, a rat-derived dental epithelial cell line, revealed that Gb4 did not promote dental epithelial cell proliferation. Interestingly, exogenous administration of Gb4 enhanced the gene expression of enamel extracellular matrix proteins such as ameloblastin, amelogenin, and enamelin in dental epithelial cells as well as in developing tooth germs. Gb4 also induced the expression of TrkB, one of the key receptors required for ameloblast induction in dental epithelial cells. In contrast, Gb4 downregulated the expression of p75, a receptor for neurotrophins (including neurotrophin-4) and a marker of undifferentiated dental epithelial cells. In addition, we found that exogenous administration of Gb4 to dental epithelial cells stimulated the extracellular signal-regulated kinase and p38 mitogen-activated protein kinase signalling pathways. Furthermore, Gb4 induced the expression of epiprofin and Runx2, the positive regulators for ameloblastin gene transcription. Thus, our results suggest that Gb4 contributes to promoting the differentiation of dental epithelial cells into ameloblasts.

Fine tuning of Rac1 and RhoA alters cuspal shapes by remolding the cellular geometry

The anatomic and functional combinations of cusps and lophs (ridges) define the tooth shape of rodent molars, which distinguishes species. The species-specific cusp patterns result from the spatiotemporal induction of enamel knots (EKs), which require precisely controlled cellular behavior to control the epithelial invagination. Despite the well-defined roles of EK in cusp patterning, the determinants of the ultimate cuspal shapes and involvement of epithelial cellular geometry are unknown. Using two typical tooth patterns, the lophodont in gerbils and the bunodont in mice, we showed that the cuspal shape is determined by the dental epithelium at the cap stage, whereas the cellular geometry in the inner dental epithelium (IDE) is correlated with the cuspal shape. Intriguingly, fine tuning Rac1 and RhoA interconvert cuspal shapes between two species by remolding the cellular geometry. Either inhibition of Rac1 or ectopic expression of RhoA could region-distinctively change the columnar shape of IDE cells in gerbils to drive invagination to produce cusps. Conversely, RhoA reduction in mice inhibited invagination and developed lophs. Furthermore, we found that Rac1 and RhoA modulate the choices of cuspal shape by coordinating adhesion junctions, actin distribution, and fibronectin localization to drive IDE invagination.

Integrin and dystroglycan compensate each other to mediate laminin-dependent basement membrane assembly and epiblast polarization

During early embryogenesis, endodermal γ1-laminin expression is required for basement membrane (BM) assembly, promoting conversion of non-polar pluripotent cells into polarized epiblast. The influence of laminin-111 (Lm111) and its integrin and dystroglycan (DG) receptors on epiblast in embryoid bodies (EBs), a model for differentiation of the embryonic plate, was further investigated. Lm111 added to the medium of EBs initiated conversion of inner nonpolar cell to the polarized epiblast epithelium with an exterior-to-central basal-to-apical orientation. Microinjection of Lm111 into EB interiors resulted in an interior BM with complete inversion of cell polarity. Lm111 assembled a BM on integrin-β1 null EBs with induction of polarization at reduced efficiency. β-Integrin compensation was not detected in these nulls with integrin adaptor proteins failing to assemble. A dimer of laminin LG domains 4-5 (LZE3) engineered to strongly bind to α-dystroglycan almost completely inhibited laminin accumulation on integrin β1-null EBs, reducing BM and ablating cell polarization. When Lm111 was incubated with integrin-β1/dystroglycan double-knockout EBs, laminin failed to accumulate on the EBs, the EBs did not differentiate, and the EBs underwent apoptosis. Collectively the findings support the hypotheses that the locus of laminin cell surface assembly can determine the axis of epithelial polarity. This requires integrin- and/or dystroglycan-dependent binding to laminin LG domains with the highest efficiency achieved when both receptors are present. Finally, EBs that cannot assemble a matrix undergo apoptosis.

Plakophilin-1, a Novel Wnt Signaling Regulator, Is Critical for Tooth Development and Ameloblast Differentiation

Tooth morphogenesis is initiated by reciprocal interactions between the ectoderm and neural crest-derived mesenchyme, and the Wnt signaling pathway is involved in this process. We found that Plakophilin (PKP)1, which is associated with diseases such as ectodermal dysplasia/skin fragility syndrome, was highly expressed in teeth and skin, and was upregulated during tooth development. We hypothesized that PKP1 regulates Wnt signaling via its armadillo repeat domain in a manner similar to β-catenin. To determine its role in tooth development, we performed Pkp1 knockdown experiments using ex vivo organ cultures and cell cultures. Loss of Pkp1 reduced the size of tooth germs and inhibited dental epithelial cell proliferation, which was stimulated by Wnt3a. Furthermore, transfected PKP1-emerald green fluorescent protein was translocated from the plasma membrane to the nucleus upon stimulation with Wnt3a and LiCl, which required the PKP1 N terminus (amino acids 161 to 270). Localization of PKP1, which is known as an adhesion-related desmosome component, shifted to the plasma membrane during ameloblast differentiation. In addition, Pkp1 knockdown disrupted the localization of Zona occludens 1 in tight junctions and inhibited ameloblast differentiation; the two proteins were shown to directly interact by immunoprecipitation. These results implicate the participation of PKP1 in early tooth morphogenesis as an effector of canonical Wnt signaling that controls ameloblast differentiation via regulation of the cell adhesion complex.

The basal chorionic trophoblast cell layer: An emerging coordinator of placenta development

During gestation, fetomaternal exchange occurs in the villous tree (labyrinth) of the placenta. Development of this structure depends on tightly coordinated cellular processes of branching morphogenesis and differentiation of specialized trophoblast cells. The basal chorionic trophoblast (BCT) cell layer that localizes next to the chorioallantoic interface is of critical importance for labyrinth morphogenesis in rodents. Gcm1-positive cell clusters within this layer initiate branching morphogenesis thereby guiding allantoic fetal blood vessels towards maternal blood sinuses. Later these cells differentiate and contribute to the syncytiotrophoblast of the fetomaternal barrier. Additional cells within the BCT layer sustain continued morphogenesis, possibly through a repopulating progenitor population. Several mouse mutants highlight the importance of a structurally intact BCT epithelium, and a growing number of studies addresses its patterning and epithelial architecture. Here, we review and discuss emerging concepts in labyrinth development focussing on the biology of the BCT cell layer.

Rho GTPases in ameloblast differentiation

During tooth development, ameloblasts differentiate from inner enamel epithelial cells to enamel-forming cells by modulating the signal pathways mediating epithelial–mesenchymal interaction and a cell-autonomous gene network. The differentiation process of epithelial cells is characterized by marked changes in their morphology and polarity, accompanied by dynamic cytoskeletal reorganization and changes in cell–cell and cell–matrix adhesion over time. Functional ameloblasts are tall, columnar, polarized cells that synthesize and secrete enamel-specific proteins. After deposition of the full thickness of enamel matrix, ameloblasts become smaller and regulate enamel maturation. Recent significant advances in the fields of molecular biology and genetics have improved our understanding of the regulatory mechanism of the ameloblast cell life cycle, mediated by the Rho family of small GTPases. They act as intracellular molecular switch that transduce signals from extracellular stimuli to the actin cytoskeleton and the nucleus. In our review, we summarize studies that provide current evidence for Rho GTPases and their involvement in ameloblast differentiation. In addition to the Rho GTPases themselves, their downstream effectors and upstream regulators have also been implicated in ameloblast differentiation.

Cell cycle control, DNA damage repair, and apoptosis-related pathways control pre-ameloblasts differentiation during tooth development

Background

Ameloblast differentiation is the most critical stepwise process in amelogenesis, and it is controlled by precise molecular events. To better understand the mechanism controlling pre-ameloblasts (PABs) differentiation into secretory ameloblasts (SABs), a more precise identification of molecules and signaling networks will elucidate the mechanisms governing enamel formation and lay a foundation for enamel regeneration.

Results

We analyzed transcriptional profiles of human PABs and SABs. From a total of 28,869 analyzed transcripts, we identified 923 differentially expressed genes (DEGs) with p < 0.05 and Fold-change > 2. Among the DEGs, 647 genes showed elevated expression in PABs compared to SABs. Notably, 38 DEGs displayed greater than eight-fold changes. Comparative analysis revealed that highly expressed genes in PABs were involved in cell cycle control, DNA damage repair and apoptosis, while highly expressed genes in SABs were related to cell adhesion and extracellular matrix. Moreover, coexpression network analysis uncovered two highly conserved sub-networks contributing to differentiation, containing transcription regulators (RUNX2, ETV1 and ETV5), solute carrier family members (SLC15A1 and SLC7A11), enamel matrix protein (MMP20), and a polymodal excitatory ion channel (TRPA1).

Conclusions

By combining comparative analysis and coexpression networks, this study provides novel biomarkers and research targets for ameloblast differentiation and the potential for their application in enamel regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1783-y) contains supplementary material, which is available to authorized users.

Molecular Basis of Laminin-Integrin Interactions

Laminins are composed of three polypeptide chains, designated as α, β, and γ. The C-terminal region of laminin heterotrimers, containing coiled-coil regions, short tails, and laminin globular (LG) domains, is necessary and sufficient for binding to integrins, which are the major laminin receptor class. Laminin recognition by integrins critically requires the α chain LG domains and a glutamic acid residue of the γ chain at the third position from the C-terminus. Furthermore, the C-terminal region of the β chain contains a short amino acid sequence that modulates laminin affinity for integrins. Thus, all three of the laminin chains act cooperatively to facilitate integrin binding. Mammals possess 5 α (α1-5), 3 β (β1-3), and 3 γ (γ1-3) chains, combinations of which give rise to 16 distinct laminin isoforms. Each isoform is expressed in a tissue-specific and developmental stage-specific manner, exerting its functions through binding of integrins. In this review, we detail the current knowledge surrounding the molecular basis and physiological relevance of specific interactions between laminins and integrins, and describe the mechanisms underlying laminin action through integrins.

Tooth germ invagination from cell-cell interaction: Working hypothesis on mechanical instability

In the early stage of tooth germ development, the bud of the dental epithelium is invaginated by the underlying mesenchyme, resulting in the formation of a cap-like folded shape. This bud-to-cap transition plays a critical role in determining the steric design of the tooth. The epithelial-mesenchymal interaction within a tooth germ is essential for mediating the bud-to-cap transition. Here, we present a theoretical model to describe the autonomous process of the morphological transition, in which we introduce mechanical interactions among cells. Based on our observations, we assumed that peripheral cells of the dental epithelium bound tightly to each other to form an elastic sheet, and mesenchymal cells that covered the tooth germ would restrict its growth. By considering the time-dependent growth of cells, we were able to numerically show that the epithelium within the tooth germ buckled spontaneously, which is reminiscent of the cap-stage form. The difference in growth rates between the peripheral and interior parts of the dental epithelium, together with the steric size of the tooth germ, were determining factors for the number of invaginations. Our theoretical results provide a new hypothesis to explain the histological features of the tooth germ.

Odontogenic Ameloblast-associated Protein (ODAM) Mediates Junctional Epithelium Attachment to Teeth via Integrin-ODAM-Rho Guanine Nucleotide Exchange Factor 5 (ARHGEF5)-RhoA Signaling

Adhesion of the junctional epithelium (JE) to the tooth surface is crucial for maintaining periodontal health. Although odontogenic ameloblast-associated protein (ODAM) is expressed in the JE, its molecular functions remain unknown. We investigated ODAM function during JE development and regeneration and its functional significance in the initiation and progression of periodontitis and peri-implantitis. ODAM was expressed in the normal JE of healthy teeth but absent in the pathologic pocket epithelium of diseased periodontium. In periodontitis and peri-implantitis, ODAM was extruded from the JE following onset with JE attachment loss and detected in gingival crevicular fluid. ODAM induced RhoA activity and the expression of downstream factors, including ROCK (Rho-associated kinase), by interacting with Rho guanine nucleotide exchange factor 5 (ARHGEF5). ODAM-mediated RhoA signaling resulted in actin filament rearrangement. Reduced ODAM and RhoA expression in integrin β₃- and β₆-knockout mice revealed that cytoskeleton reorganization in the JE occurred via integrin-ODAM-ARHGEF5-RhoA signaling. Fibronectin and laminin activated RhoA signaling via the integrin-ODAM pathway. Finally, ODAM was re-expressed with RhoA in regenerating JE after gingivectomy in vivo. These results suggest that ODAM expression in the JE reflects a healthy periodontium and that JE adhesion to the tooth surface is regulated via fibronectin/laminin-integrin-ODAM-ARHGEF5-RhoA signaling. We also propose that ODAM could be used as a biomarker of periodontitis and peri-implantitis.

Interaction between fibronectin and β1 integrin is essential for tooth development

The dental epithelium and extracellular matrix interact to ensure that cell growth and differentiation lead to the formation of teeth of appropriate size and quality. To determine the role of fibronectin in differentiation of the dental epithelium and tooth formation, we analyzed its expression in developing incisors. Fibronectin mRNA was expressed during the presecretory stage in developing dental epithelium, decreased in the secretory and early maturation stages, and then reappeared during the late maturation stage. The binding of dental epithelial cells derived from postnatal day-1 molars to a fibronectin-coated dish was inhibited by the RGD but not RAD peptide, and by a β1 integrin-neutralizing antibody, suggesting that fibronectin-β1 integrin interactions contribute to dental epithelial-cell binding. Because fibronectin and β1 integrin are highly expressed in the dental mesenchyme, it is difficult to determine precisely how their interactions influence dental epithelial differentiation in vivo. Therefore, we analyzed β1 integrin conditional knockout mice (Intβ1^lox-/lox-/K14-Cre) and found that they exhibited partial enamel hypoplasia, and delayed eruption of molars and differentiation of ameloblasts, but not of odontoblasts. Furthermore, a cyst-like structure was observed during late ameloblast maturation. Dental epithelial cells from knockout mice did not bind to fibronectin, and induction of ameloblastin expression in these cells by neurotrophic factor-4 was inhibited by treatment with RGD peptide or a fibronectin siRNA, suggesting that the epithelial interaction between fibronectin and β1 integrin is important for ameloblast differentiation and enamel formation.

Epithelial morphogenesis: the mouse eye as a model system

Morphogenesis is the developmental process by which tissues and organs acquire the shape that is critical to their function. Here, we review recent advances in our understanding of the mechanisms that drive morphogenesis in the developing eye. These investigations have shown that regulation of the actin cytoskeleton is central to shaping the presumptive lens and retinal epithelia that are the major components of the eye. Regulation of the actin cytoskeleton is mediated by Rho family GTPases, by signaling pathways and indirectly, by transcription factors that govern the expression of critical genes. Changes in the actin cytoskeleton can shape cells through the generation of filopodia (that, in the eye, connect adjacent epithelia) or through apical constriction, a process that produces a wedge-shaped cell. We have also learned that one tissue can influence the shape of an adjacent one, probably by direct force transmission, in a process we term inductive morphogenesis. Though these mechanisms of morphogenesis have been identified using the eye as a model system, they are likely to apply broadly where epithelia influence the shape of organs during development.

Effects of maternal nicotine exposure on expression of laminin alpha 5 in lung tissue of newborn

Maternal smoking has been clearly demonstrated to be associated with increased health problems in infants and children. Nicotine is the chemical substance with high level of toxicity. It crosses through the placenta and accumulates in the developing organs of fetus. Previous investigation indicated that maternal nicotine exposures induce decreased fibronectin expression in lung parenchyma. In this study, the effect of maternal nicotine exposure on laminin expression of the newborn mice lungs has been evaluated. Female pregnant Balb/C mice were divided randomly in to four groups as fallow: Experimental group 1 (Exp D1); was received 3 mg kg(-1) nicotine intra peritoneal injection (IP) from gestational day 7 (GD7) to the last day of pregnancy, Experimental group 2 (Exp D14); was received 3 mg kg(-1) nicotine from GD7 to postnatal day 14, Groups 3 and 4; as sham control groups (Sha-Con) were received the same volume (3 mg kg(-1)) of normal saline parallel to experimental groups. At the end of exposure times, all of newborns were anesthetized; their lungs were removed and prepared for immunohistochemical method and real-time polymerase chain reaction. The finding indicated that laminin alpha 5 (Lama5) mRNA expressions in the lung of newborn in the nicotine treated Exp D1 decreased by 0.63 fold but increased in Exp D14 by 1.57 fold comparing to Sh-Con groups. Lama5 immunoreactivity was not similar in different parts of the lungs including alveoli and bronchiole, having a significant increase in the experimental groups in contrast to the Sh-Con groups. However, increase in immunoreactivity observed more in Exp D14. Immunoreactivity intensity in small vessels of all experimental groups was not significantly different. These data also indicate that maternal nicotine exposure may induce abnormal laminin expression which may cause defects in lung function during life time.

Self-renewal and multilineage differentiation of mouse dental epithelial stem cells

Understanding the cellular and molecular mechanisms underlying the self-renewal and differentiation of dental epithelial stem cells (DESCs) that support the unlimited growth potential of mouse incisors is critical for developing novel tooth regenerative therapies and unraveling the pathogenesis of odontogenic tumors. However, analysis of DESC properties and regulation has been limited by the lack of an in vitro assay system and well-documented DESC markers. Here, we describe an in vitro sphere culture system to isolate the DESCs from postnatal mouse incisor cervical loops (CLs) where the DESCs are thought to reside. The dissociated cells from CLs were able to expand and form spheres for multiple generations in the culture system. Lineage tracing indicated that DESC within the spheres were epithelial in origin as evident by lineage tracing. Upon stimulation, the sphere cells differentiated into cytokeratin 14- and amelogenin-expressing and mineral material-producing cells. Compared to the CL tissue, sphere cells expressed high levels of expression of Sca-1, CD49f (also designated as integrin α6), and CD44. Fluorescence-activated cell sorting (FACS) analyses of mouse incisor CL cells further showed that the CD49f(Bright) population was enriched in sphere-forming cells. In addition, the CD49f(Bright) population includes both slow-cycling and Lgr5(+) DESCs. The in vitro sphere culture system and identification of CD49f(Bright) as a DESC marker provide a novel platform for enriching DESCs, interrogating how maintenance, cell fate determination, and differentiation of DESCs are regulated, and developing tooth regenerative therapies.

Gene evolution and functions of extracellular matrix proteins in teeth

The extracellular matrix (ECM) not only provides physical support for tissues, but it is also critical for tissue development, homeostasis and disease. Over 300 ECM molecules have been defined as comprising the "core matrisome" in mammals through the analysis of whole genome sequences. During tooth development, the structure and functions of the ECM dynamically change. In the early stages, basement membranes (BMs) separate two cell layers of the dental epithelium and the mesenchyme. Later in the differentiation stages, the BM layer is replaced with the enamel matrix and the dentin matrix, which are secreted by ameloblasts and odontoblasts, respectively. The enamel matrix genes and the dentin matrix genes are each clustered in two closed regions located on human chromosome 4 (mouse chromosome 5), except for the gene coded for amelogenin, the major enamel matrix protein, which is located on the sex chromosomes. These genes for enamel and dentin matrix proteins are derived from a common ancestral gene, but as a result of evolution, they diverged in terms of their specific functions. These matrix proteins play important roles in cell adhesion, polarity, and differentiation and mineralization of enamel and dentin matrices. Mutations of these genes cause diseases such as odontogenesis imperfect (OI) and amelogenesis imperfect (AI). In this review, we discuss the recently defined terms matrisome and matrixome for ECMs, as well as focus on genes and functions of enamel and dentin matrix proteins.

The role of bioactive nanofibers in enamel regeneration mediated through integrin signals acting upon C/EBPα and c-Jun

Enamel formation involves highly orchestrated intracellular and extracellular events; following development, the tissue is unable to regenerate, making it a challenging target for tissue engineering. We previously demonstrated the ability to trigger enamel differentiation and regeneration in the embryonic mouse incisor using a self-assembling matrix that displayed the integrin-binding epitope RGDS (Arg-Gly-Asp-Ser). To further elucidate the intracellular signaling pathways responsible for this phenomenon, we explore here the coupling response of integrin receptors to the biomaterial and subsequent downstream gene expression profiles. We demonstrate that the artificial matrix activates focal adhesion kinase (FAK) to increase phosphorylation of both c-Jun N-terminal kinase (JNK) and its downstream transcription factor c-Jun (c-Jun). Inhibition of FAK blocked activation of the identified matrix-mediated pathways, while independent inhibition of JNK nearly abolished phosphorylated-c-Jun (p-c-Jun) and attenuated the pathways identified to promote enamel regeneration. Cognate binding sites in the amelogenin promoter were identified to be transcriptionally up-regulated in response to p-c-Jun. Furthermore, the artificial matrix induced gene expression as evidenced by an increased abundance of amelogenin, the main protein expressed during enamel formation, and the CCAAT enhancer binding protein alpha (C/EBPα), which is the known activator of amelogenin expression. Elucidating these cues not only provides guidelines for the design of synthetic regenerative strategies and opportunities to manipulate pathways to regulate enamel regeneration, but can provide insight into the molecular mechanisms involved in tissue formation.

Extracellular Matrix is an Important Component of Limbal Stem Cell Niche

Extracellular matrix plays an important role in stem cell niche which maintains the undifferentiated stem cell phenotype. Human corneal epithelial stem cells are presumed to reside mainly at the limbal basal epithelium. Efforts have been made to characterize different components of the extracellular matrix that are preferentially expressed at the limbus. Mounting evidence from experimental data suggest that these components are part of the stem cell niche and play a role in the homeostasis of limbal stem cells. The extracellular matrix provides a mechanical and structural support as well as regulates cellular functions such as adhesion, migration, proliferation, self-renewal and differentiation. Optimization of the extracellular matrix components might be able to recreate an ex vivo stem cell niche to expand limbal stem cells.

Selective functionalization of nanofiber scaffolds to regulate salivary gland epithelial cell proliferation and polarity

Epithelial cell types typically lose apicobasal polarity when cultured on 2D substrates, but apicobasal polarity is required for directional secretion by secretory cells, such as salivary gland acinar cells. We cultured salivary gland epithelial cells on poly(lactic-co-glycolic acid) (PLGA) nanofiber scaffolds that mimic the basement membrane, a specialized extracellular matrix, and examined cell proliferation and apicobasal polarization. Although cells proliferated on nanofibers, chitosan-coated nanofiber scaffolds stimulated proliferation of salivary gland epithelial cells. Although apicobasal cell polarity was promoted by the nanofiber scaffolds relative to flat surfaces, as determined by the apical localization of ZO-1, it was antagonized by the presence of chitosan. Neither salivary gland acinar nor ductal cells fully polarized on the nanofiber scaffolds, as determined by the homogenous membrane distribution of the mature tight junction marker, occludin. However, nanofiber scaffolds chemically functionalized with the basement membrane protein, laminin-111, promoted more mature tight junctions, as determined by apical localization of occludin, but did not affect cell proliferation. To emulate the multifunctional capabilities of the basement membrane, bifunctional PLGA nanofibers were generated. Both acinar and ductal cell lines responded to signals provided by bifunctional scaffolds coupled to chitosan and laminin-111, demonstrating the applicability of such scaffolds for epithelial cell types.

Laminin-511: a multi-functional adhesion protein regulating cell migration, tumor invasion and metastasis

Laminins are major constituents of basement membranes. At least 16 isoforms have now been described, each with distinct spatio-temporal expression patterns and functions. The laminin-511 heterotrimer (α5β1γ1) is one of the more recent isoforms to be identified and a potent adhesive and pro-migratory substrate for a variety of normal and tumor cell lines in vitro. As our understanding of its precise function in normal tissues and in pathologies is rapidly unraveling, current evidence suggests an important regulatory role in cancer. This review describes published data on laminin-511 expression in several malignancies and experimental evidence from both in vitro and in vivo studies supporting its functional role during tumor progression. A particular emphasis is put on more recent studies from our laboratory and that of others indicating that laminin-511 contributes to tumor dissemination and metastasis in advanced breast carcinomas and other tumor types. Collectively, the experimental evidence suggests that high expression of laminin-511 has prognostic significance and that targeting tumor-laminin-511 interactions may have therapeutic potential in advanced cancer patients.

Laminin α5 guides tissue patterning and organogenesis

Laminins (LM) are extracellular matrix molecules that contribute to and are required for the formation of basement membranes. They participate in the modulation of epithelial/mesenchymal interactions and are implicated in organogenesis and maintenance of organ homeostasis. Among the LM molecules, the LM α5 chain (LMα5) is one of the most widely distributed LM in the developing and mature organism. Its presence in some basement membranes during embryogenesis is absolutely required for maintenance of basement membrane integrity and thus for proper organogenesis. LMα5 also regulates the expression of genes important for major biological processes, in part by repressing or activating signaling pathways, depending upon the physiological context.

Functional consequences of cell type-restricted expression of laminin α5 in mouse placental labyrinth and kidney glomerular capillaries

The labyrinth is the highly vascularized part of the rodent placenta that allows efficient transfer of gases, nutrients, wastes, and other molecules between the maternal and embryonic circulations. These two blood compartments are separated by blastocyst-derived trophoblasts and endothelial cells with an intervening basement membrane that contains laminin and other typical basement membrane components. Previously we reported that the labyrinth of laminin α5 knockout (LMα5−/−) embryos exhibits reduced vascularization and detachment of endothelial cells from the basement membrane, which normally contains LMα5. As very little is known about the origin of this vascular basement membrane, we investigated the cellular requirements for LMα5 expression in the mouse placental labyrinth. By fluorescence-activated cell sorting and RT-PCR we confirmed that both endothelial cells and trophoblasts normally express LMα5. Using Cre-loxP technology and doxycycline-mediated gene expression, we generated genetically mosaic placentas in which either the trophoblasts or the endothelial cells, but not both, expressed LMα5. We found that the overall architecture of the labyrinth was normal as long as one of these two cell types expressed LMα5, even if it was transgene-derived human laminin α5. These results suggest that laminin trimers containing α5 that are synthesized and secreted by endothelium or by trophoblasts are capable of integrating into the basement membrane and promoting normal vascularization of the placenta. Additional studies showed that endothelium-expressed human LMα5 can support vascularization of the kidney glomerulus, consistent with previous studies using a tissue grafting approach.

Characterization of natural, decellularized and reseeded porcine tooth bud matrices

Dental tissue engineering efforts have yet to identify scaffolds that instruct the formation of bioengineered teeth of predetermined size and shape. Here we investigated whether extracellular matrix (ECM) molecules present in natural tooth scaffolds can provide insight on how to achieve this goal. We describe methods to effectively decellularize and demineralize porcine molar tooth buds, while preserving natural ECM protein gradients. Natural tooth ECM composition was assessed using histological and immunohistochemical (IHC) analyses of fibrillar and basement membrane proteins. Our results showed that Collagen I, Fibronectin, Collagen IV, and Laminin gradients were detected in natural tooth tissues, and retained in decellularized samples. Second harmonic generation (SHG) image analysis and 3D reconstructions were used to show that natural tooth tissue exhibited higher collagen fiber density, and less oriented and less organized collagen fibers, as compared to decellularized tooth tissue. We also found that reseeded decellularized tooth scaffolds exhibited distinctive collagen content and organization as compared to decelluarized scaffolds. Our results show that SHG allows for quantitative assessment of ECM features that are not easily characterized using traditional histological analyses. In summary, our results demonstrate the potential for natural decellularized molar tooth ECM to instruct dental cell matrix synthesis, and lay the foundation for future use of biomimetic scaffolds for dental tissue engineering applications.

Epithelial-specific knockout of the Rac1 gene leads to enamel defects

The Ras-related C3 botulinum toxin substrate 1 (Rac1) gene encodes a 21-kDa GTP-binding protein belonging to the RAS superfamily. RAS members play important roles in controlling focal adhesion complex formation and cytoskeleton contraction, activities with consequences for cell growth, adhesion, migration, and differentiation. To examine the role(s) played by RAC1 protein in cell-matrix interactions and enamel matrix biomineralization, we used the Cre/loxP binary recombination system to characterize the expression of enamel matrix proteins and enamel formation in Rac1 knockout mice (Rac1(-/-)). Mating between mice bearing the floxed Rac1 allele and mice bearing a cytokeratin 14-Cre transgene generated mice in which Rac1 was absent from epithelial organs. Enamel of the Rac1 conditional knockout mouse was characterized by light microscopy, backscattered electron imaging in the scanning electron microscope, microcomputed tomography, and histochemistry. Enamel matrix protein expression was analyzed by western blotting. Major findings showed that the Tomes' processes of Rac1(-/-) ameloblasts lose contact with the forming enamel matrix in unerupted teeth, the amounts of amelogenin and ameloblastin are reduced in Rac1(-/-) ameloblasts, and after eruption, the enamel from Rac1(-/-) mice displays severe structural defects with a complete loss of enamel. These results support an essential role for RAC1 in the dental epithelium involving cell-matrix interactions and matrix biomineralization.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Identification of active sequences in the L4a domain of laminin α5 promoting neurite elongation

Laminin α5 is an extracellular matrix protein containing multiple domains implicated in various biological processes, such as embryogenesis and renal function. In this study, we used recombinant proteins and synthetic peptides to identify amino acid residues within the short arm region of α5 that were critical for neurite outgrowth activity. The short arm of α5 contains three globular domains (LN, L4a, and L4b) and three rodlike elements (LEa, LEb, and LEc). Recombinant proteins comprised of the α5 short arm fused with a Fc tag produced in 293 cells were assayed for PC12 (pheochromocytoma) cell adhesion and neurite outgrowth activities. Although it did not have cell attachment activity, neurite outgrowth was promoted by the recombinant protein. To narrow the region involved in neurite outgrowth activity, two truncated recombinant proteins were produced in 293 cells. A recombinant protein lacking L4a and LEb lost activity. Furthermore, we synthesized 78 partially overlapping peptides representing most of the amino acid sequences of L4a and LEb. Of the peptides, A5-76 [mouse laminin α5 928-939 (TSPDLFRLVFRY) in L4a] exhibited neurite outgrowth activity. Mutagenesis studies showed that Phe(933) and Arg(934) were involved in neurite outgrowth activity. Moreover, inhibition assays using anti-integrin monoclonal antibodies showed that neurite outgrowth on the α5 short arm was partially mediated by integrin α1β1. However, the antibodies to integrin α1 and β1 did not inhibit neurite elongation on the A5-76 peptide. These results suggest that in addition to cellular interactions with the active site in the L4a domain, the binding of integrin α1β1 seems to modulate neurite elongation on the short arm of α5.