Lysophosphatidic acid cooperates with EGF in inducing branching morphogenesis of embryonic mouse salivary epithelium

Comparative transcriptome analysis reveals conserved branching morphogenesis related genes involved in chamber formation of catfish swimbladder

The swimbladder is an internal gas-filled organ in teleosts. Its major function is to regulate buoyancy. The swimbladder exhibits great variation in size, shape, and number of compartments or chambers among teleosts. However, genomic control of swimbladder variation is unknown. Channel catfish ( Ictalurus punctatus), blue catfish ( Ictalurus furcatus), and their F1 hybrids of female channel catfish × male blue catfish (C × B hybrid catfish) provide a good model in which to investigate the swimbladder morphology, because channel catfish possess a single-chambered swimbladder, whereas blue catfish possess a bichambered swimbladder; C × B hybrid catfish possess a bichambered swimbladder but with a significantly reduced posterior chamber. Here we determined the transcriptional profiles of swimbladder from channel catfish, blue catfish, and C × B hybrid catfish. We examined their transcriptomes at both the fingerling and adult stages. Through comparative transcriptome analysis, ~4,000 differentially expressed genes (DEGs) were identified. Among these DEGs, members of the Wnt signaling pathway ( wnt1, wnt2, nfatc1, rac2), Hedgehog signaling pathway ( shh), and growth factors ( fgf10, igf-1) were identified. As these genes were known to be important for branching morphogenesis of mammalian lung and of mammary glands, their association with budding of the posterior chamber primordium and progressive development of bichambered swimbladder in fish suggest that these branching morphogenesis-related genes and their functions in branching are evolutionarily conserved across a broad spectrum of species.

The contribution of specific cell subpopulations to submandibular salivary gland branching morphogenesis

Branching morphogenesis is the developmental program responsible for generating a large surface to volume ratio in many secretory and absorptive organs. To accomplish branching morphogenesis, spatiotemporal regulation of specific cell subpopulations is required. Here, we review recent studies that define the contributions of distinct cell subpopulations to specific cellular processes during branching morphogenesis in the mammalian submandibular salivary gland, including the initiation of the gland, the coordination of cleft formation, and the contribution of stem/progenitor cells to morphogenesis. In conclusion, we provide an overview of technological advances that have opened opportunities to further probe the contributions of specific cell subpopulations and to define the integration of events required for branching morphogenesis.

Role of LPA and the Hippo pathway on apoptosis in salivary gland epithelial cells

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid involved in numerous physiological responses. However, the expression of LPA receptors and the role of the Hippo signaling pathway in epithelial cells have remained elusive. In this experiment, we studied the functional expression of LPA receptors and the associated signaling pathway using reverse transcriptase–PCR, microspectrofluorimetry, western blotting and immunocytochemistry in salivary gland epithelial cells. We found that LPA receptors are functionally expressed and involved in activating the Hippo pathway mediated by YAP/TAZ through Lats/Mob1 and RhoA/ROCK. Upregulation of YAP/TAZ-dependent target genes, including CTGF, ANKRD1 and CYR61, has also been observed in LPA-treated cells. In addition, based on data suggesting that tumor necrosis factor (TNF)-α induces cell apoptosis, LPA upregulates TNF-induced caspase-3 and cleaved Poly(ADP-ribose)polymerase (PARP). However, small interfering RNA treatment to Yes-associated protein (YAP) or transcriptional co-activator with a PDZ-binding motif (TAZ) significantly decreased TNF-α- and LPA-induced apoptosis, suggesting that YAP and TAZ modulate the apoptotic pathway in salivary epithelial cells.

COMPARISON OF PLGA, PCL, AND CHITOSAN IN SALIVARY GLAND BRANCHING MORPHOGENESIS

Branching morphogenesis is a fundamental morphogenetic process in generating glandular tissues. Although the mechanism of branching morphogenesis has been well-explored in the salivary gland development, its interaction with different biodegradable materials has never been investigated. For the purpose of salivary gland regeneration, recapitulation of morphogenetic processes on biodegradable materials might be requisite. Toward this aim, biodegradable biomaterials including poly-lactic-co-glycolic acid (PLGA), poly-epsilon-caprolactone (PCL), and chitosan were examined in the submandibular gland (SMG) culture systems to elucidate their possible impact on salivary morphogenesis. It was found that when SMG explants were cultured on PLGA and PCL, the explants failed to form well-developed branching phenotypes with limited cell migration (5.6 ± 8.8 μm; 10.0 ± 14.1 μm) and decreasing cell viability (56.9% ± 12.5%; 50.3% ± 8.1%). On the contrary, explants cultured on chitosan showed well-developed branches, which were superior in number to those on the control substrata, without any alteration of the morphogenetic phenotypes. Furthermore, the increased cell migration (267.8 ± 45.2 μm) and explants viability (146.8% ± 18.4%) along with the greater deposition of type III collagen, altogether account for better SMG morphogenesis on chitosan. According to the results, it was found that branching morphogenesis of SMG was affected by different biodegradable materials. Chitosan might be an appropriate biodegradable material for salivary morphogenesis, and has applicable potential in the regeneration of salivary tissue.

Astrocytes treated by lysophosphatidic acid induce axonal outgrowth of cortical progenitors through extracellular matrix protein and epidermal growth factor signaling pathway

Lysophosphatidic acid (LPA) plays important roles in many biological processes, such as brain development, oncogenesis and immune functions, via its specific receptors. We previously demonstrated that LPA-primed astrocytes induce neuronal commitment of cerebral cortical progenitors (Spohr et al. 2008). In the present study, we analyzed neurite outgrowth induced by LPA-treated astrocytes and the molecular mechanism underlying this event. LPA-primed astrocytes increase neuronal differentiation, arborization and neurite outgrowth of developing cortical neurons. Treatment of astrocytes with epidermal growth factor (EGF) ligands yielded similar results, suggesting that members of the EGF family might mediate LPA-induced neuritogenesis. Furthermore, treatment of astrocytes with LPA or EGF ligands led to an increase in the levels of the extracellular matrix molecule, laminin (LN), thus enhancing astrocyte permissiveness to neurite outgrowth. This event was reversed by pharmacological inhibitors of the MAPK signaling pathway and of the EGF receptor. Our data reveal an important role of astrocytes and EGF receptor ligands pathway as mediators of bioactive lipids action in brain development, and implicate the LN and MAPK pathway in this process.

Chitin-based materials in tissue engineering: applications in soft tissue and epithelial organ

Chitin-based materials and their derivatives are receiving increased attention in tissue engineering because of their unique and appealing biological properties. In this review, we summarize the biomedical potential of chitin-based materials, specifically focusing on chitosan, in tissue engineering approaches for epithelial and soft tissues. Both types of tissues play an important role in supporting anatomical structures and physiological functions. Because of the attractive features of chitin-based materials, many characteristics beneficial to tissue regeneration including the preservation of cellular phenotype, binding and enhancement of bioactive factors, control of gene expression, and synthesis and deposition of tissue-specific extracellular matrix are well-regulated by chitin-based scaffolds. These scaffolds can be used in repairing body surface linings, reconstructing tissue structures, regenerating connective tissue, and supporting nerve and vascular growth and connection. The novel use of these scaffolds in promoting the regeneration of various tissues originating from the epithelium and soft tissue demonstrates that these chitin-based materials have versatile properties and functionality and serve as promising substrates for a great number of future applications.

Evidence of interlobular repulsion during branching morphogenesis in mouse salivary glands

We developed a culture method for detecting repulsion among epithelial lobules during branching morphogenesis in mouse submandibular glands. Three epithelia were placed at each vertex of an imaginary triangle apart but near enough to meet with one another if each of them expands radially during the culture period. No repulsion was observed following cultivation with neuregulin 1 and lysophosphatidic acid; the epithelia actively branched and nearly contacted one another in the triangle's center. In contrast, strong repulsion was observed among the epithelia cultured with fibroblast growth factor 1 (FGF1), which exhibited less branching and moved away from the center. The localization of DiI- (1,1', di-octadecyl-3,3,3',3',-tetramethylindo-carbocyanine perchlorate) and BrdU- (5-bromodeoxyuridine) labeled cells in the cultures exposed to FGF1 indicated that the cells were unable to move and proliferate in the center. SB431542, an inhibitor of transforming growth factor-beta (TGFbeta) signaling, was unable to abolish this repulsion, suggesting that TGFbetas will not probably act as repellants in this case.

Oligodendrocyte-spinal cord explant co-culture: an in vitro model for the study of myelination

The in vitro models developed to investigate the growth and myelination of axons, such as dorsal root ganglion (DRG)-Schwann cell co-culture, DRG-oligodendrocyte co-culture and central nervous system (CNS) neuron-oligodendrocyte co-culture, have provided an effective way to reveal the mechanisms that underlie the interaction between neurons and myelin-forming cells. In order to better understand the complex process of myelination during CNS development and spinal cord repair, we established a rat spinal cord neuron-oligodendrocyte co-culture model. In this co-culture system, the spinal cord explants were used as the source of neurons, and the oligodendrocytes were induced from GFP-oligodendrocyte precursor cells (GFP-OPCs). The results showed that the GFP-oligodendrocytes that differentiated from GFP-OPCs in co-culture attached to the neurites growing out from the spinal cord explants and formed myelin structures. As the oligodendrocytes expressed GFP, and the neuron somas remained in the explants, the interaction between oligodendrocytes and neurites in co-culture were observed clearly and dynamically without immunostaining.

Small-molecule antagonist of macrophage migration inhibitory factor enhances migratory response of mesenchymal stem cells to bronchial epithelial cells

Human mesenchymal stem cells (MSCs) from bone marrow stroma can home to and repair injured tissue, but the rate of engraftment is generally low. Regulating migration-related signaling of MSCs may be a powerful strategy to enhance this process. To gain insight into the molecular mechanisms governing homing, we identified negative factors affecting MSC migration using an in vitro model of injured lung. Heat-labile factors in bovine pituitary extract, a component of serum-free epithelial medium, inhibited more than 97% of MSC migration. This was partly due to a dose-dependent response to macrophage migration inhibitory factor (MIF). Eighty-five ng/mL recombinant MIF, the concentration found in the epithelial medium, inhibited about 50% of MSC migration. Media conditioning by uninjured or bleomycin-injured bronchial epithelial cells partially attenuated this suppressive effect. Additionally, the anti-inflammatory agent ISO-1, a small-molecule MIF antagonist, further increased MSC migration by nearly fourfold in conditioned epithelial media. This is the first report of the effect of MIF and ISO-1 on MSC migration, and the data suggest that MIF and its antagonists may have therapeutic applications in controlling MSC homing during repair of injured lung and in other clinically relevant systems.

Chitosan cooperates with mesenchyme-derived factors in regulating salivary gland epithelial morphogenesis

Chitosan is a widely used biocompatible biomaterial in the tissue regeneration, but its utility and application in the tissue morphogenesis of salivary gland remains unclear. The study aimed to explore the effects of chitosan on the epithelial morphogenesis of submandibular gland (SMG). With chitosan, the branching morphogenesis of the whole SMG explant was facilitated, and the morphogenetic-promoting effects of mesenchymal tissue on SMG were further enhanced. Furthermore, chitosan was competent to induce recombined SMG epithelium to form branches in the serum-free condition independently. In the presence of chitosan, the morphogenetic efficacy of mesenchyme-derived growth factors responsible for epithelial morphogenesis including fibroblast growth factors 7, fibroblast growth factor 10 and hepatocyte growth factor increased. The specific epithelial phenotype induced by individual growth factor, which was required for the accomplishment of salivary epithelial morphogenesis, was promoted by chitosan. Moreover, the proliferative and the chemotactic properties of these growth factors towards the SMG epithelia were also reinforced by chitosan. Therefore, in orchestrating and intensifying the essential mesenchyme-derived growth factors, chitosan is versatile in mediating SMG epithelium to form a predetermined phenotype more efficiently and comprehensively. This study suggested that chitosan is a morphogenetic-regulating biomaterial for salivary tissue, which might be useful for the future salivary gland investigation and regeneration.

FGF alters epithelial competence for EGF at the initiation of branching morphogenesis of mouse submandibular gland

Embryonic day 13 mouse submandibular gland (E13-SMG) rudiments with two to four clefts have been commonly used in culture experiments to show that growth factors, such as epidermal growth factor (EGF) -family and fibroblast growth factor (FGF) -family ligands, are involved in branching morphogenesis. In the present study, we focused on E12 rudiments and attempted to elucidate the roles of EGF- and FGF-family ligands in SMG development from E12 to E13. In mesenchyme-free, Matrigel-embedded cultures, EGF + lysophosphatidic acid (LPA) induced branching in E13 epithelium, whereas E12 epithelium remained spherical and no branching occurred under the same culture conditions; however, both E12 and E13 epithelia elongated in response to FGF10. Reverse transcriptase-polymerase chain reaction studies showed that the expression of ErbB1 among four EGF receptors and Lpa3 among three LPA receptors was lower in E12 than in E13 epithelia. Fgf10, Fgf7, and their major receptor Fgfr2b were highly and equally expressed in E12 and E13 rudiments. After 24 hr of mesenchyme-free culture with FGF10 or FGF7, E12 epithelium was primed to initiate branching morphogenesis in response to EGF + LPA coincident with ErbB1 and Lpa3 up-regulation. These results suggest that the EGF-family ligand-receptor system is undeveloped at E12 and that it becomes primed on E13 by the FGF ligand-receptor system to play an important role in the induction of branching morphogenesis.

Molecular analysis of endoderm regionalization

We have engaged in a number of studies in our laboratory that have focused on the molecular mechanisms underlying gut formation, with particular attention being paid to the establishment of regional differences found in the entire gut and within each digestive organ. We have found from our analyses that the presumptive fate of the endoderm in the embryos of vertebrates is determined quite early during development, but the realization of this fate often requires molecular cues from the neighboring tissues such as the lateral plate mesoderm and the mesenchyme derived from it. The mesenchyme seems often to exert instructive or supportive induction effects and, in some cases, a completely inhibitory role during the differentiation of the endodermal epithelium. In addition, many reports on the formation of the stomach, intestine, liver and salivary gland in vertebrates, and of Drosophila gut, all indicate that the morphogenesis and cytodifferentiation of these organs are regulated by the regulated expression of genes encoding growth factors and transcription factors. We have further shown that the epithelium can regulate the differentiation of the mesenchyme into the connective tissue and the smooth muscle layers, thus demonstrating the occurrence of literally interactive processes in the development of the digestive organs.