Signaling pathways activated by epidermal growth factor receptor or fibroblast growth factor receptor differentially regulate branching morphogenesis in fetal mouse submandibular glands

Ser252Trp mutation in fibroblast growth factor receptor 2 promotes branching morphogenesis in mouse salivary glands

OBJECTIVES

The purpose of this study was to perform morphological and immunohistochemical (IHC) analysis of the submandibular glands (SMGs) in early development in Apert syndrome model mice (Ap mice).

METHODS

ACTB-Cre homozygous mice were mated with fibroblast growth factor receptor 2 (Fgfr2+/Neo-S252W) mice; ACTB-Cre heterozygous mice (ACTB-Cre mice) at embryonic day (E) 13.5 served as the control group, and Fgfr2+/S252W mice (Ap mice) served as the experimental group. Hematoxylin and eosin (H&E) staining was performed on SMGs; Total SMG area and epithelial area were determined, and the epithelial occupancy ratio was calculated. Immunostaining was performed to assess the localization of FGF signaling-related proteins. Next, bromodeoxyuridine (BrdU)-positive cells were evaluated to assess cell proliferation. Finally, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to assess apoptosis in SMGs.

RESULTS

The epithelial occupancy ratio was significantly higher in SMGs of Ap mice compared with that in SMGs of controls. FGF7 and bone morphogenetic protein 4 (BMP4) exhibited different localizations in SMGs of Ap mice compared with SMGs of controls. Cell proliferation was higher in SMGs of Ap mice compared with that of controls; however, apoptosis did not different significantly between the two groups.

CONCLUSION

Our results suggest that enhanced FGF signaling conferred by missense mutations in FGFR2 promotes branching morphogenesis in SMGs of Ap mice.

Cryopreservation of Biologically Functional Submandibular Gland Rudiments from Fetal Mice

BACKGROUND/AIM

Cryopreservation of cell lines has been widely used in the laboratory; however, cryopreservation of organs is still considered to be difficult. The submandibular gland (SMG) of fetal mice is one of the best-characterized organs. We investigated the conditions for cryopreserving SMG rudiments.

MATERIALS AND METHODS

Embryonic day 13 SMG rudiments were cryopreserved with or without a cryoprotectant. They were thawed and incubated in DMEM/F12 medium. Moreover, the influence of EGF stimulation on the signaling cascade after frozen-thawing the rudiments was analyzed by Western blotting.

RESULTS

When SMG rudiments were cryopreserved without a cryoprotectant, all cells in the rudiments died. However, the SMG rudiments that had been preserved in a cryoprotectant showed branching morphogenesis. Additionally, the responsiveness of signaling cascades to EGF did not differ between frozen with a cryoprotectant and non-frozen rudiments.

CONCLUSION

Cryopreservation might be a useful technology for preserving tissues from small organs, such as fetal SMG rudiments.

Regulatory mechanisms of branching morphogenesis in mouse submandibular gland rudiments

Branching morphogenesis is an important developmental process for many organs, including the salivary glands. Whereas epithelial–mesenchymal interactions, which are cell-to-cell communications, are known to drive branching morphogenesis, the molecular mechanisms responsible for those inductive interactions are still largely unknown. Cell growth factors and integrins are known to be regulators of branching morphogenesis of salivary glands. In addition, functional microRNAs (miRNAs) have recently been reported to be present in the developing submandibular gland. In this review, the authors describe the roles of various cell growth factors, integrins and miRNAs in branching morphogenesis of developmental mouse submandibular glands.

Identification of the protective mechanisms of Lactoferrin in the irradiated salivary gland

Radiotherapy is commonly used in patients with head and neck cancer, and usually results in irreversible salivary glands damage and hypofunction. It is therefore important to manage such irradiation to prevent damage to the salivary glands. A previous study showed that Lactoferrin (LF) has a radioprotective effect, but the mechanism was not determined in salivary glands. In the present study, we investigated the detailed radioprotective effect of LF using both ex vivo submandibular salivary gland organ culture and ICR male mice in vivo. We found that LF had effects on both cell proliferation and CyclinD1-mediated cell-cycle progression which were regulated via the ERK1/2 and AKT signal transduction pathways. In addition, LF affected acinar cell structure and function after irradiation. These findings suggest that LF may be a useful agent to prevent irradiation effects in salivary glands.

FGF and EDA pathways control initiation and branching of distinct subsets of developing nasal glands

Hypertrophy, hyperplasia and altered mucus secretion from the respiratory submucosal glands (SMG) are characteristics of airway diseases such as cystic fibrosis, asthma and chronic bronchitis. More commonly, hyper-secretion of the nasal SMGs contributes to allergic rhinitis and upper airway infection. Considering the role of these glands in disease states, there is a significant dearth in understanding the molecular signals that regulate SMG development and patterning. Due to the imperative role of FGF signalling during the development of other branched structures, we investigated the role of Fgf10 during initiation and branching morphogenesis of murine nasal SMGs. Fgf10 is expressed in the mesenchyme around developing SMGs while expression of its receptor Fgfr2 is seen within glandular epithelial cells. In the Fgf10 null embryo, Steno's gland and the maxillary sinus gland were completely absent while other neighbouring nasal glands showed normal duct elongation but defective branching. Interestingly, the medial nasal glands were present in Fgf10 homozygotes but missing in Fgfr2b mutants, with expression of Fgf7 specifically expressed around these developing glands, indicating that Fgf7 might compensate for loss of Fgf10 in this group of glands. Intriguingly the lateral nasal glands were only mildly affected by loss of FGF signalling, while these glands were missing in Eda mutant mice, where the Steno's and maxillary sinus gland developed as normal. This analysis reveals that regulation of nasal gland development is complex with different subsets of glands being regulated by different signalling pathways. This analysis helps shed light on the nasal gland defects observed in patients with hypohidrotic ectodermal dysplasia (HED) (defect EDA pathway) and LADD syndrome (defect FGFR2b pathway).

Prediction of Growth Factor-Dependent Cleft Formation During Branching Morphogenesis Using A Dynamic Graph-Based Growth Model

This study considers the problem of describing and predicting cleft formation during the early stages of branching morphogenesis in mouse submandibular salivary glands (SMG) under the influence of varied concentrations of epidermal growth factors (EGF). Given a time-lapse video of a growing SMG, first we build a descriptive model that captures the underlying biological process and quantifies the ground truth. Tissue-scale (global) and morphological features related to regions of interest (local features) are used to characterize the biological ground truth. Second, we devise a predictive growth model that simulates EGF-modulated branching morphogenesis using a dynamic graph algorithm, which is driven by biological parameters such as EGF concentration, mitosis rate, and cleft progression rate. Given the initial configuration of the SMG, the evolution of the dynamic graph predicts the cleft formation, while maintaining the local structural characteristics of the SMG. We determined that higher EGF concentrations cause the formation of higher number of buds and comparatively shallow cleft depths. Third, we compared the prediction accuracy of our model to the Glazier-Graner-Hogeweg (GGH) model, an on-lattice Monte-Carlo simulation model, under a specific energy function parameter set that allows new rounds of de novo cleft formation. The results demonstrate that the dynamic graph model yields comparable simulations of gland growth to that of the GGH model with a significantly lower computational complexity. Fourth, we enhanced this model to predict the SMG morphology for an EGF concentration without the assistance of a ground truth time-lapse biological video data; this is a substantial benefit of our model over other similar models that are guided and terminated by information regarding the final SMG morphology. Hence, our model is suitable for testing the impact of different biological parameters involved with the process of branching morphogenesis in silico, while reducing the requirement of in vivo experiments.

Mechanisms of fibroblast growth factor signaling in the ovarian follicle

Fibroblast growth factors (FGFs) have been shown to alter growth and differentiation of reproductive tissues in a variety of species. Within the female reproductive tract, the effects of FGFs have been focused on the ovary, and the most studied one is FGF2, which stimulates granulosa cell proliferation and decreases differentiation (decreased steroidogenesis). Other FGFs have also been implicated in ovarian function, and this review summarizes the effects of members of two subfamilies on ovarian function; the FGF7 subfamily that also contains FGF10, and the FGF8 subfamily that also contains FGF18. There are data to suggest that FGF8 and FGF18 have distinct actions on granulosa cells, despite their apparent similar receptor binding properties. Studies of non-reproductive developmental biology also indicate that FGF8 is distinct from FGF18, and that FGF7 is also distinct from FGF10 despite similar receptor binding properties. In this review, the potential mechanisms of differential action of FGF7/FGF10 and FGF8/FGF18 during organogenesis will be reviewed and placed in the context of follicle development. A model is proposed in which FGF8 and FGF18 differentially activate receptors depending on the properties of the extracellular matrix in the follicle.

Cellular and physical mechanisms of branching morphogenesis

Branching morphogenesis is the developmental program that builds the ramified epithelial trees of various organs, including the airways of the lung, the collecting ducts of the kidney, and the ducts of the mammary and salivary glands. Even though the final geometries of epithelial trees are distinct, the molecular signaling pathways that control branching morphogenesis appear to be conserved across organs and species. However, despite this molecular homology, recent advances in cell lineage analysis and real-time imaging have uncovered surprising differences in the mechanisms that build these diverse tissues. Here, we review these studies and discuss the cellular and physical mechanisms that can contribute to branching morphogenesis.

Cell-based multi-parametric model of cleft progression during submandibular salivary gland branching morphogenesis

Cleft formation during submandibular salivary gland branching morphogenesis is the critical step initiating the growth and development of the complex adult organ. Previous experimental studies indicated requirements for several epithelial cellular processes, such as proliferation, migration, cell-cell adhesion, cell-extracellular matrix (matrix) adhesion, and cellular contraction in cleft formation; however, the relative contribution of each of these processes is not fully understood since it is not possible to experimentally manipulate each factor independently. We present here a comprehensive analysis of several cellular parameters regulating cleft progression during branching morphogenesis in the epithelial tissue of an early embryonic salivary gland at a local scale using an on lattice Monte-Carlo simulation model, the Glazier-Graner-Hogeweg model. We utilized measurements from time-lapse images of mouse submandibular gland organ explants to construct a temporally and spatially relevant cell-based 2D model. Our model simulates the effect of cellular proliferation, actomyosin contractility, cell-cell and cell-matrix adhesions on cleft progression, and it was used to test specific hypotheses regarding the function of these parameters in branching morphogenesis. We use innovative features capturing several aspects of cleft morphology and quantitatively analyze clefts formed during functional modification of the cellular parameters. Our simulations predict that a low epithelial mitosis rate and moderate level of actomyosin contractility in the cleft cells promote cleft progression. Raising or lowering levels of contractility and mitosis rate resulted in non-progressive clefts. We also show that lowered cell-cell adhesion in the cleft region and increased cleft cell-matrix adhesions are required for cleft progression. Using a classifier-based analysis, the relative importance of these four contributing cellular factors for effective cleft progression was determined as follows: cleft cell contractility, cleft region cell-cell adhesion strength, epithelial cell mitosis rate, and cell-matrix adhesion strength.

Branching morphogenesis is a complex and dynamic embryonic process that creates the structure of many adult organs, including the salivary gland. During this process, many cellular changes occur in the epithelial cells, including changes in cell-cell adhesions, cell-extracellular matrix (matrix) adhesions, cell proliferation, and cellular contraction, resulting in formation of clefts in the epithelial cells of the organ. A comprehensive understanding of the relative contributions of these cellular processes has crucial therapeutic implications for organ regeneration and functional restoration of organ structure in diseased salivary glands. Here, we have developed a cell-based model of cleft progression and simulated cleft progression under conditions of altered cell-cell adhesions, cellular contractility, cell-matrix adhesion and cell proliferation to identify the optimum cellular conditions that cause clefts to progress. The model predicts that cleft progression requires a moderate level of cleft cell contractility, a low epithelial proliferation rate, reduced cell-cell adhesion strength in the cleft and high cell-matrix adhesion strength also in the cleft region. The results of our classification analysis demonstrate that cellular contractility in the cleft cells has a significant effect on cleft progression, followed by cell-cell adhesion strength, rate of cell proliferation, and strength of cell-matrix adhesion energies.

MT2-MMP-dependent release of collagen IV NC1 domains regulates submandibular gland branching morphogenesis

Proteolysis is essential during branching morphogenesis, but the roles of MT-MMPs and their proteolytic products are not clearly understood. Here, we discover that decreasing MT-MMP activity during submandibular gland branching morphogenesis decreases proliferation and increases collagen IV and MT-MMP expression. Specifically, reducing epithelial MT2-MMP profoundly decreases proliferation and morphogenesis, increases Col4a2 and intracellular accumulation of collagen IV, and decreases the proteolytic release of collagen IV NC1 domains. Importantly, we demonstrate the presence of collagen IV NC1 domains in developing tissue. Furthermore, recombinant collagen IV NC1 domains rescue branching morphogenesis after MT2-siRNA treatment, increasing MT-MMP and proproliferative gene expression via beta1 integrin and PI3K-AKT signaling. Additionally, HBEGF also rescues MT2-siRNA treatment, increasing NC1 domain release, proliferation, and MT2-MMP and Hbegf expression. Our studies provide mechanistic insight into how MT2-MMP-dependent release of bioactive NC1 domains from collagen IV is critical for integrating collagen IV synthesis and proteolysis with epithelial proliferation during branching morphogenesis.