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

[Role of Fibroblast Growth Factor 7 in Craniomaxillofacial Development]

Craniomaxillofacial development involves a series of highly ordered temporal-spatial cellular differentiation processes in which a variety of cell signaling factors, such as fibroblast growth factors, play important regulatory roles. As a classic fibroblast growth factor, fibroblast growth factor 7 (FGF7) serves a wide range of regulatory functions. Previous studies have demonstrated that FGF7 regulates the proliferation and migration of epithelial cells, protects them, and promotes their repair. Furthermore, recent findings indicate that epithelial cells are not the only ones subjected to the broad and powerful regulatory capacity of FGF7. It has potential effects on skeletal system development as well. In addition, FGF7 plays an important role in the development of craniomaxillofacial organs, such as the palate, the eyes, and the teeth. Nonetheless, the role of FGF7 in oral craniomaxillofacial development needs to be further elucidated. In this paper, we summarized the published research on the role of FGF7 in oral craniomaxillofacial development to demonstrate the overall understanding of FGF7 and its potential functions in oral craniomaxillofacial development.

FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

Septum submucosal glands exhibit aberrant morphology and reduced mucin production in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is characterized by significant accumulation and thickening of mucus in the sinonasal cavities. One contributor of aberrant mucus production and impaired mucociliary clearance (MCC) is altered function of the sinonasal submucosal glands (SMGs), yet contributions of SMGs to upper airway disease initiation and progression remain unknown. The objective of this study was to characterize the morphology and secretory cell identities of the nasal septum SMGs in both healthy and CRS adults.

METHODS

Biopsies from adult participants with CRS without nasal polyps (CRSsNP, n = 4), CRS with nasal polyps (CRSwNP, n = 8), and non-CRS controls (n = 14) were collected from the posterior septum. Glandular morphology and mucus markers were investigated using histological techniques and high-resolution confocal microscopy.

RESULTS

Analysis revealed a significant decrease in gland density in the posterior septum of CRSsNP (28% ± 6.15%) and CRSwNP (23% ± 3.09%) compared to control participants (53% ± 1.59%, p < 0.0001). Further analysis of the CRS SMG secretory function revealed an overall decrease in Mucin 5B+ gland mucus being produced. Dilated and cystic ductal structures filled with inspissated mucus were also common to CRS glands.

CONCLUSION

Here, we describe a significant alteration in SMG structure and function in the adult CRS posterior septum suggesting reduced gland contribution to MCC. The SMGs of both the nose and sinuses may represent targets for future therapeutic approaches.

FGF10 is an essential regulator of tracheal submucosal gland morphogenesis

Mucus secretion and mucociliary clearance are crucial processes required to maintain pulmonary homeostasis. In the trachea and nasal passages, mucus is secreted by submucosal glands (SMGs) that line the airway, with an additional contribution from goblet cells of the surface airway epithelium. The SMG mucus is rich in mucins and antimicrobial enzymes. Defective tracheal SMGs contribute to hyper-secretory respiratory diseases, such as cystic fibrosis, asthma, and chronic obstructive pulmonary disease, however little is known about the signals that regulate their morphogenesis and patterning. Here, we show that Fgf10 is essential for the normal development of murine tracheal SMGs, with gland development arresting at the early bud stage in the absence of FGF10 signalling. As Fgf10 knockout mice are lethal at birth, inducible knockdown of Fgf10 at late embryonic stages was used to follow postnatal gland formation, confirming the essential role of FGF10 in SMG development. In heterozygous Fgf10 mice the tracheal glands formed but with altered morphology and restricted distribution. The reduction in SMG branching in Fgf10 heterozygous mice was not rescued with time and resulted in a reduction in overall tracheal mucus secretion. Fgf10 is therefore a key signal in SMG development, influencing both the number of glands and extent of branching morphogenesis, and is likely, therefore, to play a role in aspects of SMG-dependent respiratory health.

Bones, Glands, Ears and More: The Multiple Roles of FGF10 in Craniofacial Development

Members of the fibroblast growth factor (FGF) family have myriad functions during development of both non-vertebrate and vertebrate organisms. One of these family members, FGF10, is largely expressed in mesenchymal tissues and is essential for postnatal life because of its critical role in development of the craniofacial complex, as well as in lung branching. Here, we review the function of FGF10 in morphogenesis of craniofacial organs. Genetic mouse models have demonstrated that the dysregulation or absence of FGF10 function affects the process of palate closure, and FGF10 is also required for development of salivary and lacrimal glands, the inner ear, eye lids, tongue taste papillae, teeth, and skull bones. Importantly, mutations within the FGF10 locus have been described in connection with craniofacial malformations in humans. A detailed understanding of craniofacial defects caused by dysregulation of FGF10 and the precise mechanisms that underlie them offers new opportunities for development of medical treatments for patients with birth defects and for regenerative approaches for cancer patients with damaged gland tissues.

A six-gene expression toolbox for the glands, epithelium and chondrocytes in the mouse nasal cavity

The nose is the central feature of the amniote face. In adults, the nose is a structurally and functionally complex organ that consists of bone, cartilage, glands and ducts. In an ongoing expression screen in our lab, we found several novel markers for specific tissues in the nasal region. Here, using in situ hybridization expression experiments, we report that Alx1, Ap-2β, Crispld1, Eya4, Moxd1, and Penk have tissue specific expression during murine nasal development. At E11.5, we observed that Alx1, Ap-2β, Crispld1, and Eya4 are expressed in the medial and lateral nasal prominences. We found that Moxd1 and Penk are expressed in the lateral nasal prominences. At E15.5, Alx1 is expressed in nasal septum. Ap-2β and Crispld1 are expressed in nasal glands and cartilages. Eya4 is expressed in olfactory epithelium. Intriguingly at E15.5 Moxd1 is expressed in all the nasal cartilage while the expression of Penk is restricted to chondrocytes contributing to the posterior nasal septum. The expression domains reported here suggest that these genes warrant functional studies to determine their role in nasal capsule morphogenesis.