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

Col4a1 mutations cause progressive retinal neovascular defects and retinopathy

Mutations in collagen, type IV, alpha 1 (COL4A1), a major component of basement membranes, cause multisystem disorders in humans and mice. In the eye, these include anterior segment dysgenesis, optic nerve hypoplasia and retinal vascular tortuosity. Here we investigate the retinal pathology in mice carrying dominant-negative Col4a1 mutations. To this end, we examined retinas longitudinally in vivo using fluorescein angiography, funduscopy and optical coherence tomography. We assessed retinal function by electroretinography and studied the retinal ultrastructural pathology. Retinal examinations revealed serous chorioretinopathy, retinal hemorrhages, fibrosis or signs of pathogenic angiogenesis with chorioretinal anastomosis in up to approximately 90% of Col4a1 mutant eyes depending on age and the specific mutation. To identify the cell-type responsible for pathogenesis we generated a conditional Col4a1 mutation and determined that primary vascular defects underlie Col4a1-associated retinopathy. We also found focal activation of Müller cells and increased expression of pro-angiogenic factors in retinas from Col4a1(+/Δex41)mice. Together, our findings suggest that patients with COL4A1 and COL4A2 mutations may be at elevated risk of retinal hemorrhages and that retinal examinations may be useful for identifying patients with COL4A1 and COL4A2 mutations who are also at elevated risk of hemorrhagic strokes.

Regulatory Mechanisms Driving Salivary Gland Organogenesis

Salivary glands develop as highly branched structures designed to produce and secrete saliva. Advances in mouse genetics, stem cell biology, and regenerative medicine are having a tremendous impact on our understanding of salivary gland organogenesis. Understanding how submandibular gland (SMG) initiation, branching morphogenesis, and cell differentiation occur, as well as defining the progenitor/stem cells and cell and tissue interactions that drive SMG development will help guide regenerative approaches for patients suffering from loss of salivary gland function. This review focuses on recent literature from the past 5 years investigating the regulatory mechanisms driving SMG organogenesis.

Proteases decode the extracellular matrix cryptome

The extracellular matrix is comprised of 1100 core-matrisome and matrisome-associated proteins and of glycosaminoglycans. This structural scaffold contributes to the organization and mechanical properties of tissues and modulates cell behavior. The extracellular matrix is dynamic and undergoes constant remodeling, which leads to diseases if uncontrolled. Bioactive fragments, called matricryptins, are released from the extracellular proteins by limited proteolysis and have biological activities on their own. They regulate numerous physiological and pathological processes such as angiogenesis, cancer, diabetes, wound healing, fibrosis and infectious diseases and either improve or worsen the course of diseases depending on the matricryptins and on the molecular and biological contexts. Several protease families release matricryptins from core-matrisome and matrisome-associated proteins both in vitro and in vivo. The major proteases, which decrypt the extracellular matrix, are zinc metalloproteinases of the metzincin superfamily (matrixins, adamalysins and astacins), cysteine proteinases and serine proteases. Some matricryptins act as enzyme inhibitors, further connecting protease and matricryptin fates and providing intricate regulation of major physiopathological processes such as angiogenesis and tumorigenesis. They strengthen the role of the extracellular matrix as a key player in tissue failure and core-matrisome and matrisome-associated proteins as important therapeutic targets.

Peptide-modified Substrate for Modulating Gland Tissue Growth and Morphology In Vitro

In vitro fabricated biological tissue would be a valuable tool to screen newly synthesized drugs or understand the tissue development process. Several studies have attempted to fabricate biological tissue in vitro. However, controlling the growth and morphology of the fabricated tissue remains a challenge. Therefore, new techniques are required to modulate tissue growth. RGD (arginine-glycine-aspartic acid), which is an integrin-binding domain of fibronectin, has been found to enhance cell adhesion and survival; it has been used to modify substrates for in vitro cell culture studies or used as tissue engineering scaffolds. In addition, this study shows novel functions of the RGD peptide, which enhances tissue growth and modulates tissue morphology in vitro. When an isolated submandibular gland (SMG) was cultured on an RGD-modified alginate hydrogel sheet, SMG growth including bud expansion and cleft formation was dramatically enhanced. Furthermore, we prepared small RGD-modified alginate beads and placed them on the growing SMG tissue. These RGD-modified beads successfully induced cleft formation at the bead position, guiding the desired SMG morphology. Thus, this RGD-modified material might be a promising tool to modulate tissue growth and morphology in vitro for biological tissue fabrication.

Chitosan facilitates structure formation of the salivary gland by regulating the basement membrane components

Tissue structure is important for inherent physiological function and should be recapitulated during tissue engineering for regenerative purposes. The salivary gland is a branched organ that is responsible for saliva secretion and regulation. The salivary glands develop from epithelial-mesenchymal interactions, and depend on the support of the basement membrane (BM). Chitosan-based biomaterials have been demonstrated to be competent in facilitating the formation of salivary gland tissue structure. However, the underlying mechanisms have remained elusive. In the developing submandibular gland (SMG), the chitosan effect was found to diminish when collagen and laminin were removed from cultured SMG explants. Chitosan increased the expression of BM components including collagen, laminin, and heparan sulfate proteoglycan, and also facilitated BM components and the corresponding receptors to be expressed in tissue-specific patterns beneficial for SMG branching. The chitosan effect decreased when either laminin components or receptors were inhibited, as well when the downstream signaling was blocked. Our results revealed that chitosan promotes salivary glands branching through the BM. By regulating BM components and receptors, chitosan efficiently stimulated downstream signaling to facilitate salivary gland branching. The present study revealed the underlying mechanism of the chitosan effect in engineering SMG structure formation.

Salivary gland development and disease

Mammalian salivary glands synthesize and secrete saliva via a vast interconnected network of epithelial tubes attached to secretory end units. The extensive morphogenesis required to establish this organ is dependent on interactions between multiple cell types (epithelial, mesenchymal, endothelial, and neuronal) and the engagement of a wide range of signaling pathways. Here we describe critical regulators of salivary gland development and discuss how mutations in these impact human organogenesis. In particular, we explore the genetic contribution of growth factor pathways, nerve-derived factors and extracellular matrix molecules to salivary gland formation in mice and humans.

Heterotypic control of basement membrane dynamics during branching morphogenesis

Many mammalian organs undergo branching morphogenesis to create highly arborized structures with maximized surface area for specialized organ function. Cooperative cell-cell and cell-matrix adhesions that sculpt the emerging tissue architecture are guided by dynamic basement membranes. Properties of the basement membrane are reciprocally controlled by the interacting epithelial and mesenchymal cell populations. Here we discuss how basement membrane remodeling is required for branching morphogenesis to regulate cell-matrix and cell-cell adhesions that are required for cell patterning during morphogenesis and how basement membrane impacts morphogenesis by stimulation of cell patterning, force generation, and mechanotransduction. We suggest that in addition to creating mature epithelial architecture, remodeling of the epithelial basement membrane during branching morphogenesis is also essential to promote maturation of the stromal mesenchyme to create mature organ structure. Recapitulation of developmental cell-matrix and cell-cell interactions are of critical importance in tissue engineering and regeneration strategies that seek to restore organ function.

Hyaluronan/RHAMM interactions in mesenchymal tumor pathogenesis: role of growth factors

Fibrosarcoma belongs to the sarcoma cancer group, which are spindle cell malignancies of mesenchymal origin, and owe their name to the predominant cell line that is present within the tumor. The extracellular matrix (ECM) is a complicated structure that surrounds and supports cells within tissues. Its main components are proteoglycans, collagens, glycoproteins, hyaluronan (HA), and several matrix-degrading enzymes. During cancer progression, significant changes can be observed in the structural and mechanical properties of ECM components. The ECM provides a physical scaffold to which tumor cells attach and migrate. Thus, it is required for key cellular events such as cell motility, adhesion, proliferation, invasion, and metastasis. Importantly, fibrosarcomas were shown to have a high content and turnover of ECM components including HA, proteoglycans, collagens, fibronectin, and laminin. In this review, we will focus on the HA component of fibrosarcoma ECM and critically discuss its role and involved mechanisms during fibrosarcoma pathogenesis.

Loss of CD147 results in impaired epithelial cell differentiation and malformation of the meibomian gland

Meibomian gland dysfunction is a leading cause of ocular surface disease. However, little is known about the regulatory processes that control the development and maintenance of this sebaceous gland. Here, we identify a novel function for CD147, a transmembrane protein that promotes tissue remodeling through induction of matrix metalloproteinases, in regulating meibocyte differentiation and activity. We found that CD147 localized along basal cells and within discrete membrane domains of differentiated meibocytes in glandular acini containing gelatinolytic activity. Induction of meibocyte differentiation in vitro promoted CD147 clustering and MMP9 secretion, whereas RNAi-mediated abrogation of CD147 impaired MMP9 secretion, concomitant with a reduction in the number of proliferative cells and cytoplasmic lipids. Meibomian glands of CD147 knockout mice had a lower number of acini in both the superior and inferior tarsal plates of the eyelids, and were characterized by loss of lipid-filled meibocytes compared with control mice. Together, our data provide evidence showing that gelatinolytic activity in meibocytes is dependent on CD147, and supports a role for CD147 in maintaining the normal development and function of the meibomian gland.

Membrane-type matrix metalloproteinases: Their functions and regulations

Membrane-type matrix metalloproteinases (MT-MMPs) form a subgroup of the matrix metalloproteinase (MMP) family, and there are 6 MT-MMPs in humans. MT-MMPs are further sub-classified into type I transmembrane-type (MT1, -MT2-, MT3- and MT5-MMPs) and glycosylphosphatidylinositol (GPI)-anchored type (MT4- and MT6-MMPs). In either case MT-MMPs are tethered to the plasma membrane, and this cell surface expression provides those enzymes with unique functionalities affecting various cellular behaviours. Among the 6 MT-MMPs, MT1-MMP is the most investigated enzyme and many of its roles and regulations have been revealed to date, but the potential roles and regulatory mechanisms of other MT-MMPs are gradually getting clearer as well. Further investigations of MT-MMPs are likely to reveal novel pathophysiological mechanisms and potential therapeutic strategies for different diseases in the future.

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.

Manipulating the murine lacrimal gland

The lacrimal gland (LG) secretes aqueous tears necessary for maintaining the structure and function of the cornea, a transparent tissue essential for vision. In the human a single LG resides in the orbit above the lateral end of each eye delivering tears to the ocular surface through 3 - 5 ducts. The mouse has three pairs of major ocular glands, the most studied of which is the exorbital lacrimal gland (LG) located anterior and ventral to the ear. Similar to other glandular organs, the LG develops through the process of epithelial branching morphogenesis in which a single epithelial bud within a condensed mesenchyme undergoes multiple rounds of bud and duct formation to form an intricate interconnected network of secretory acini and ducts. This elaborate process has been well documented in many other epithelial organs such as the pancreas and salivary gland. However, the LG has been much less explored and the mechanisms controlling morphogenesis are poorly understood. We suspect that this under-representation as a model system is a consequence of the difficulties associated with finding, dissecting and culturing the LG. Thus, here we describe dissection techniques for harvesting embryonic and post-natal LG and methods for ex vivo culture of the tissue.

Local and global dynamics of the basement membrane during branching morphogenesis require protease activity and actomyosin contractility

Many epithelial tissues expand rapidly during embryonic development while remaining surrounded by a basement membrane. Remodeling of the basement membrane is assumed to occur during branching morphogenesis to accommodate epithelial growth, but how such remodeling occurs is not yet clear. We report that the basement membrane is highly dynamic during branching of the salivary gland, exhibiting both local and global remodeling. At the tip of the epithelial end bud, the basement membrane becomes perforated by hundreds of well-defined microscopic holes at regions of rapid expansion. Locally, this results in a distensible, mesh-like basement membrane for controlled epithelial expansion while maintaining tissue integrity. Globally, the basement membrane translocates rearward as a whole, accumulating around the forming secondary ducts, helping to stabilize them during branching. Both local and global dynamics of the basement membrane require protease and myosin II activity. Our findings suggest that the basement membrane is rendered distensible by proteolytic degradation to allow it to be moved and remodeled by cells through actomyosin contractility to support branching morphogenesis.

LIM kinase regulation of cytoskeletal dynamics is required for salivary gland branching morphogenesis

LIMK regulation of actin and microtubule dynamics is required for epithelial regulation of early- and late-stage cleft stabilization and progression. LIMK stimulates focal adhesion assembly and integrin β1 activation in cleft regions, causing fibronectin fibrillogenesis and promoting cleft progression during salivary gland branching morphogenesis.

Coordinated actin microfilament and microtubule dynamics is required for salivary gland development, although the mechanisms by which they contribute to branching morphogenesis are not defined. Because LIM kinase (LIMK) regulates both actin and microtubule organization, we investigated the role of LIMK signaling in mouse embryonic submandibular salivary glands using ex vivo organ cultures. Both LIMK 1 and 2 were necessary for branching morphogenesis and functioned to promote epithelial early- and late-stage cleft progression through regulation of both microfilaments and microtubules. LIMK-dependent regulation of these cytoskeletal systems was required to control focal adhesion protein–dependent fibronectin assembly and integrin β1 activation, involving the LIMK effectors cofilin and TPPP/p25, for assembly of the actin- and tubulin-based cytoskeletal systems, respectively. We demonstrate that LIMK regulates the early stages of cleft formation—cleft initiation, stabilization, and progression—via establishment of actin stability. Further, we reveal a novel role for the microtubule assembly factor p25 in regulating stabilization and elongation of late-stage progressing clefts. This study demonstrates the existence of multiple actin- and microtubule-dependent stabilization steps that are controlled by LIMK and are required in cleft progression during branching morphogenesis.

Biocompatible tissue scaffold compliance promotes salivary gland morphogenesis and differentiation

Substrate compliance is reported to alter cell phenotype, but little is known about the effects of compliance on cell development within the context of a complex tissue. In this study, we used 0.48 and 19.66 kPa polyacrylamide gels to test the effects of the substrate modulus on submandibular salivary gland development in culture and found a significant decrease in branching morphogenesis in explants grown on the stiff 19.66 kPa gels relative to those grown on the more physiologically compliant 0.48 kPa gels. While proliferation and apoptosis were not affected by the substrate modulus, tissue architecture and epithelial acinar cell differentiation were profoundly perturbed by aberrant, high stiffness. The glands cultured on 0.48 kPa gels were similar to developing glands in morphology and expression of the differentiation markers smooth muscle alpha-actin (SM α-actin) in developing myoepithelial cells and aquaporin 5 (AQP5) in proacinar cells. At 19.66 kPa, however, tissue morphology and the expression and distribution of SM α-actin and AQP5 were disrupted. Significantly, aberrant gland development at 19.66 kPa could be rescued by both mechanical and chemical stimuli. Transfer of glands from 19.66 to 0.48 kPa gels resulted in substantial recovery of acinar structure and differentiation, and addition of exogenous transforming growth factor beta 1 at 19.66 kPa resulted in a partial rescue of morphology and differentiation within the proacinar buds. These results indicate that environmental compliance is critical for organogenesis, and suggest that both mechanical and chemical stimuli can be exploited to promote organ development in the contexts of tissue engineering and organ regeneration.

Extracellular matrix determinants and the regulation of cancer cell invasion stratagems

During development, wound repair and disease-related processes, such as cancer, normal, or neoplastic cell types traffic through the extracellular matrix (ECM), the complex composite of collagens, elastin, glycoproteins, proteoglycans, and glycosaminoglycans that dictate tissue architecture. Current evidence suggests that tissue-invasive processes may proceed by protease-dependent or protease-independent strategies whose selection is not only governed by the characteristics of the motile cell population, but also by the structural properties of the intervening ECM. Herein, we review the mechanisms by which ECM dimensionality, elasticity, crosslinking, and pore size impact patterns of cell invasion. This summary should prove useful when designing new experimental approaches for interrogating invasion programs as well as identifying potential cellular targets for next-generation therapeutics.

Salivary gland development: a template for regeneration

The mammalian salivary gland develops as a highly branched structure designed to produce and secrete saliva. This review will focus on research on mouse submandibular gland development and the translation of this basic research toward therapy for patients suffering from salivary hypofunction. Here we review the most recent literature that has enabled a better understanding of the mechanisms of salivary gland development. Additionally, we discuss approaches proposed to restore salivary function using gene and cell-based therapy. Increasing our understanding of the developmental mechanisms involved during development is critical to design effective therapies for regeneration and repair of damaged glands.

Lysyl oxidase in colorectal cancer

Colorectal cancer is the third most prevalent form of cancer worldwide and fourth-leading cause of cancer-related mortality, leading to ~600,000 deaths annually, predominantly affecting the developed world. Lysyl oxidase is a secreted, extracellular matrix-modifying enzyme previously suggested to act as a tumor suppressor in colorectal cancer. However, emerging evidence has rapidly implicated lysyl oxidase in promoting metastasis of solid tumors and in particular colorectal cancer at multiple stages, affecting tumor cell proliferation, invasion, and angiogenesis. This emerging research has stimulated significant interest in lysyl oxidase as a strong candidate for developing and deploying inhibitors as functional efficacious cancer therapeutics. In this review, we discuss the rapidly expanding body of knowledge concerning lysyl oxidase in solid tumor progression, highlighting recent advancements in the field of colorectal cancer.

Molecular cues for development and regeneration of salivary glands

The hypofunction of salivary glands caused by Sjögren's Syndrome or radiotherapy for head and neck cancer significantly compromises the quality of life of millions patients. Currently no curative treatment is available for the irreversible hyposalivation, whereas regenerative strategies targeting salivary stem/progenitor cells are promising. However, the success of these strategies is constrained by the lack of insights on the molecular cues of salivary gland regeneration. Recent advances in the molecular controls of salivary gland morphogenesis provided valuable clues for identifying potential regenerative cues. A complicated network of signaling molecules between epithelia, mesenchyme, endothelia, extracellular matrix and innervating nerves orchestrate the salivary gland organogenesis. Here we discuss the roles of several cross-talking intercellular signaling pathways, i.e., FGF, Wnt, Hedgehog, Eda, Notch, Chrm1/HB-EGF and Laminin/Integrin pathways, in the development of salivary glands and their potentials to promote salivary regeneration.

Extracellular metalloproteinases in neural crest development and craniofacial morphogenesis

The neural crest (NC) is a population of migratory stem/progenitor cells that is found in early vertebrate embryos. NC cells are induced during gastrulation, and later migrate to multiple destinations and contribute to many types of cells and tissues, such as craniofacial structures, cardiac tissues, pigment cells and the peripheral nervous system. Recently, accumulating evidence suggests that many extracellular metalloproteinases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAMs with thrombospondin motifs (ADAMTSs), play important roles in various stages of NC development. Interference with metalloproteinase functions often causes defects in craniofacial structures, as well as in other cells and tissues that are contributed by NC cells, in humans and other vertebrates. In this review, we summarize the current state of the field concerning the roles of these three families of metalloproteinases in NC development and related tissue morphogenesis, with a special emphasis on craniofacial morphogenesis.

The roles of hyaluronan/RHAMM/CD44 and their respective interactions along the insidious pathways of fibrosarcoma progression

Fibrosarcomas are rare malignant mesenchymal tumors originating from fibroblasts. Importantly, fibrosarcoma cells were shown to have a high content and turnover of extracellular matrix (ECM) components including hyaluronan (HA), proteoglycans, collagens, fibronectin, and laminin. ECMs are complicated structures that surround and support cells within tissues. During cancer progression, significant changes can be observed in the structural and mechanical properties of the ECM components. Importantly, hyaluronan deposition is usually higher in malignant tumors as compared to benign tissues, predicting tumor progression in some tumor types. Furthermore, activated stromal cells are able to produce tissue structure rich in hyaluronan in order to promote tumor growth. Key biological roles of HA result from its interactions with its specific CD44 and RHAMM (receptor for HA-mediated motility) cell-surface receptors. HA-receptor downstream signaling pathways regulate in turn cellular processes implicated in tumorigenesis. Growth factors, including PDGF-BB, TGFβ2, and FGF-2, enhanced hyaluronan deposition to ECM and modulated HA-receptor expression in fibrosarcoma cells. Indeed, FGF-2 through upregulation of specific HAS isoforms and hyaluronan synthesis regulated secretion and net hyaluronan deposition to the fibrosarcoma pericellular matrix modulating these cells' migration capability. In this paper we discuss the involvement of hyaluronan/RHAMM/CD44 mediated signaling in the insidious pathways of fibrosarcoma progression.

Strategies to increase drug penetration in solid tumors

Despite significant improvement in modalities for treatment of cancer that led to a longer survival period, the death rate of patients with solid tumors has not changed during the last decades. Emerging studies have identified several physical barriers that limit the therapeutic efficacy of cancer therapeutic agents such as monoclonal antibodies, chemotherapeutic agents, anti-tumor immune cells, and gene therapeutics. Most solid tumors are of epithelial origin and, although malignant cells are de-differentiated, they maintain intercellular junctions, a key feature of epithelial cells, both in the primary tumor as well as in metastatic lesions. Furthermore, nests of malignant epithelial tumor cells are shielded by layers of extracellular matrix (ECM) proteins (e.g., collagen, elastin, fibronectin, laminin) whereby tumor vasculature rarely penetrates into the tumor nests. In this chapter, we will review potential strategies to modulate the ECM and epithelial junctions to enhance the intratumoral diffusion and/or to remove physical masking of target receptors on malignant cells. We will focus on peptides that bind to the junction protein desmoglein 2 and trigger intracellular signaling, resulting in the transient opening of intercellular junctions. Intravenous injection of these junction openers increased the efficacy and safety of therapies with monoclonal antibodies, chemotherapeutics, and T cells in mouse tumor models and was safe in non-human primates. Furthermore, we will summarize approaches to transiently degrade ECM proteins or downregulate their expression. Among these approaches is the intratumoral expression of relaxin or decorin after adenovirus- or stem cell-mediated gene transfer. We will provide examples that relaxin-based approaches increase the anti-tumor efficacy of oncolytic viruses, monoclonal antibodies, and T cells.

How integrins control breast biology

This article explores new ideas about how the ECM-integrin axis controls normal and malignant breast biology. We discuss the role of integrins in mammary stem cells, and how cell-matrix interactions regulate ductal and alveolar development and function. We also examine the contribution of integrins to tissue disorganisation and metastasis, and how an altered stromal and ECM tumour microenvironment affects the cancer cell niche both within primary tumours and at distant sites. Finally, we mention novel strategies for integrin-directed breast cancer treatment.

Parasympathetic stimulation improves epithelial organ regeneration

Parasympathetic nerves are a vital component of the progenitor cell niche during development, maintaining a pool of progenitors for organogenesis. Injured adult organs do not regenerate after parasympathectomy, and there are few treatments to improve organ regeneration, particularly after damage by therapeutic irradiation. Here we show that restoring parasympathetic function with the neurotrophic factor neurturin increases epithelial organ regeneration after damage. We use mouse salivary gland explant culture containing fluorescently-labeled progenitors, and injure the tissue with irradiation. The progenitors survive, parasympathetic function is diminished, and epithelial apoptosis reduces expression of neurturin, which increases neuronal apoptosis. Treatment with neurturin reduces neuronal apoptosis, restores parasympathetic function, and increases epithelial regeneration. Furthermore adult human salivary glands damaged by irradiation also have reduced parasympathetic innervation. We propose that neurturin will protect the parasympathetic nerves from damage and improve organ regeneration. This concept may be applicable for other organs where parasympathetic innervation influences their function.

Snai1 is important for avian epicardial cell transformation and motility

BACKGROUND

Formation of the epicardium requires several cellular processes including migration, transformation, invasion, and differentiation in order to give rise to fibroblast, smooth muscle, coronary endothelial and myocyte cell lineages within the developing myocardium. Snai1 is a zinc finger transcription factor that plays an important role in regulating cell survival and fate during embryonic development and under pathological conditions. However, its role in avian epicardial development has not been examined.

RESULTS

Here we show that Snai1 is highly expressed in epicardial cells from as early as the proepicardial cell stage and its expression is maintained as proepicardial cells migrate and spread over the surface of the myocardium and undergo epicardial-to-mesenchymal transformation in the generation of epicardial-derived cells. Using multiple in vitro assays, we show that Snai1 overexpression in chick explants enhances proepicardial cell migration at Hamburger Hamilton Stage (HH St.) 16, and epicardial-to-mesenchymal transformation, cell migration, and invasion at HH St. 24. Further, we demonstrate that Snai1-mediated cell migration requires matrix metalloproteinase activity, and MMP15 is sufficient for this process.

CONCLUSIONS

Together our data provide new insights into the multiple roles that Snai1 has in regulating avian epicardial development.

MT2-MMP expression during early avian morphogenesis

Membrane-type 2 matrix metalloproteinase (MT2-MMP; also called MMP15) is a membrane-bound protease that degrades extracellular matrix and activates proMMPs such as proMMP-2. MMP-2 expression in avian embryos is well documented, but it is not clear how proMMP-2 is activated during avian embryogenesis. Herein, we report that MT2-MMP mRNA is expressed in several tissues including the neural folds and epidermal ectoderm, intermediate mesoderm, pharyngeal arches, limb buds, and dermis. Several, but not all, of these tissues are known to express MMP-2. These observations suggest MT2-MMP may play a role during embryonic development not only through its own proteolytic activity but also by activating proMMP-2.

O-glycosylation modulates integrin and FGF signalling by influencing the secretion of basement membrane components

Extracellular microenvironments have crucial roles in modulating cell interactions during development. Here we discover that a conserved protein modification (O-glycosylation) influences extracellular matrix composition during mammalian organogenesis, affecting integrin signalling and fibroblast growth factor-mediated cell proliferation. Specifically, mice deficient for an enzyme (Galnt1) that adds sugars to proteins during early stages of organogenesis resulted in intracellular accumulation of major basement membrane proteins and endoplasmic reticulum stress, with resultant effects on fibroblast growth factor signalling, epithelial cell proliferation and organ growth. Exogenous addition of basement membrane components rescued fibroblast growth factor signalling and the growth defects in a β1-integrin-dependent manner. Our work demonstrates for the first time that O-glycosylation influences the composition of the extracellular matrix during mammalian organ development, influencing specific aspects of the endoplasmic reticulum stress response, cell signalling, cell proliferation and organ growth. Our work provides insight into the role of this conserved protein modification in both development and disease.

The extracellular matrix: a dynamic niche in cancer progression

The local microenvironment, or niche, of a cancer cell plays important roles in cancer development. A major component of the niche is the extracellular matrix (ECM), a complex network of macromolecules with distinctive physical, biochemical, and biomechanical properties. Although tightly controlled during embryonic development and organ homeostasis, the ECM is commonly deregulated and becomes disorganized in diseases such as cancer. Abnormal ECM affects cancer progression by directly promoting cellular transformation and metastasis. Importantly, however, ECM anomalies also deregulate behavior of stromal cells, facilitate tumor-associated angiogenesis and inflammation, and thus lead to generation of a tumorigenic microenvironment. Understanding how ECM composition and topography are maintained and how their deregulation influences cancer progression may help develop new therapeutic interventions by targeting the tumor niche.

A secreted MMP is required for reepithelialization during wound healing

Matrix metalloproteinases (MMPs) are extracellular proteases highly expressed at wound sites. However, the precise function of MMPs during reepithelialization in vivo has been elusive in mammalian models because of the high level of redundancy among the 24 mammalian MMPs. For this reason we used Drosophila melanogaster, whose genome encodes only two MMPs-one secreted type (Mmp1) and one membrane-anchored type (Mmp2)-to study the function and regulation of the secreted class of MMPs in vivo. In the absence of redundancy, we found that the Drosophila secreted MMP, Mmp1, is required in the epidermis to facilitate reepithelialization by remodeling the basement membrane, promoting cell elongation and actin cytoskeletal reorganization, and activating extracellular signal-regulated kinase signaling. In addition, we report that the jun N-terminal kinase (JNK) pathway upregulates Mmp1 expression after wounding, but that Mmp1 is expressed independent of the JNK pathway in unwounded epidermis. When the JNK pathway is ectopically activated to overexpress Mmp1, the rate of healing is accelerated in an Mmp1-dependent manner. A primary function of Mmp1, under the control of the JNK pathway, is to promote basement membrane repair, which in turn may permit cell migration and the restoration of a continuous tissue.

Normal morphogenesis of epithelial tissues and progression of epithelial tumors

Epithelial cells organize into various tissue architectures that largely maintain their structure throughout the life of an organism. For decades, the morphogenesis of epithelial tissues has fascinated scientists at the interface of cell, developmental, and molecular biology. Systems biology offers ways to combine knowledge from these disciplines by building integrative models that are quantitative and predictive. Can such models be useful for gaining a deeper understanding of epithelial morphogenesis? Here, we take inventory of some recurring themes in epithelial morphogenesis that systems approaches could strive to capture. Predictive understanding of morphogenesis at the systems level would prove especially valuable for diseases such as cancer, where epithelial tissue architecture is profoundly disrupted.

ROCK1-directed basement membrane positioning coordinates epithelial tissue polarity

The basement membrane is crucial for epithelial tissue organization and function. However, the mechanisms by which basement membrane is restricted to the basal periphery of epithelial tissues and the basement membrane-mediated signals that regulate coordinated tissue organization are not well defined. Here, we report that Rho kinase (ROCK) controls coordinated tissue organization by restricting basement membrane to the epithelial basal periphery in developing mouse submandibular salivary glands, and that ROCK inhibition results in accumulation of ectopic basement membrane throughout the epithelial compartment. ROCK-regulated restriction of PAR-1b (MARK2) localization in the outer basal epithelial cell layer is required for basement membrane positioning at the tissue periphery. PAR-1b is specifically required for basement membrane deposition, as inhibition of PAR-1b kinase activity prevents basement membrane deposition and disrupts overall tissue organization, and suppression of PAR-1b together with ROCK inhibition prevents interior accumulations of basement membrane. Conversely, ectopic overexpression of wild-type PAR-1b results in ectopic interior basement membrane deposition. Significantly, culture of salivary epithelial cells on exogenous basement membrane rescues epithelial organization in the presence of ROCK1 or PAR-1b inhibition, and this basement membrane-mediated rescue requires functional integrin β1 to maintain epithelial cell-cell adhesions. Taken together, these studies indicate that ROCK1/PAR-1b-dependent regulation of basement membrane placement is required for the coordination of tissue polarity and the elaboration of tissue structure in the developing submandibular salivary gland.

Extracellular matrix degradation and remodeling in development and disease

The extracellular matrix (ECM) serves diverse functions and is a major component of the cellular microenvironment. The ECM is a highly dynamic structure, constantly undergoing a remodeling process where ECM components are deposited, degraded, or otherwise modified. ECM dynamics are indispensible during restructuring of tissue architecture. ECM remodeling is an important mechanism whereby cell differentiation can be regulated, including processes such as the establishment and maintenance of stem cell niches, branching morphogenesis, angiogenesis, bone remodeling, and wound repair. In contrast, abnormal ECM dynamics lead to deregulated cell proliferation and invasion, failure of cell death, and loss of cell differentiation, resulting in congenital defects and pathological processes including tissue fibrosis and cancer. Understanding the mechanisms of ECM remodeling and its regulation, therefore, is essential for developing new therapeutic interventions for diseases and novel strategies for tissue engineering and regenerative medicine.

miR-200c regulates FGFR-dependent epithelial proliferation via Vldlr during submandibular gland branching morphogenesis

The regulation of epithelial proliferation during organ morphogenesis is crucial for normal development, as dysregulation is associated with tumor formation. Non-coding microRNAs (miRNAs), such as miR-200c, are post-transcriptional regulators of genes involved in cancer. However, the role of miR-200c during normal development is unknown. We screened miRNAs expressed in the mouse developing submandibular gland (SMG) and found that miR-200c accumulates in the epithelial end buds. Using both loss- and gain-of-function, we demonstrated that miR-200c reduces epithelial proliferation during SMG morphogenesis. To identify the mechanism, we predicted miR-200c target genes and confirmed their expression during SMG development. We discovered that miR-200c targets the very low density lipoprotein receptor (Vldlr) and its ligand reelin, which unexpectedly regulate FGFR-dependent epithelial proliferation. Thus, we demonstrate that miR-200c influences FGFR-mediated epithelial proliferation during branching morphogenesis via a Vldlr-dependent mechanism. miR-200c and Vldlr may be novel targets for controlling epithelial morphogenesis during glandular repair or regeneration.

Salivary gland organogenesis

Our understanding of vertebrate salivary gland organogenesis has been largely informed by the study of the developing mouse submandibular gland (SMG), which will be the major focus of this review. The mouse SMG has been historically used as a model system to study epithelial-mesenchymal interactions, growth factor-extracellular matrix (ECM) interactions, and branching morphogenesis. SMG organogenesis involves interactions between a variety of cell types and their stem/progenitor cells, including the epithelial, neuronal, and mesenchymal cells, and their ECM microenvironment, or niche. Here, we will review recent literature that provides conceptual advances in understanding the molecular mechanisms of salivary gland development. We will describe SMG organogenesis, introduce the model systems used to study development, and outline the key signaling pathways and cellular processes involved. We will also review recent research focusing on the identification of stem/progenitor cells in the SMG and how they are directed along a series of cell fate decisions to form a functional gland. The mechanisms that drive SMG organogenesis provide a template to regenerate functional salivary glands in patients who suffer from salivary hypofunction due to irreversible glandular damage after irradiation or removal of tumors. Additionally, these mechanisms may also control growth and development of other organ systems.

Characterization of a non-fibrillar-related collagen in the mollusc Haliotis tuberculata and its biological activity on human dermal fibroblasts

In invertebrates, members of the collagen family have been found in various phyla. Surprisingly, in mollusc, little is known about such molecules. In this study, we characterize the full-length abalone type IV collagen and we analysed its biological effects on human fibroblast in order to gain insights about this molecule in molluscs and particularly clues about its roles. We screened a cDNA library of Haliotis tuberculata hemocytes. The expression pattern of the transcript is determined using real-time polymerase chain reaction and in situ hybridization. The close identity between α1(IV) C-terminal domain and the vertebrate homologue led us to produce, purify and test in vitro a recombinant protein corresponding to this region using human dermal fibroblasts cell culture. The biological effects were evaluated on proliferation and on differentiation. We found that the 5,334-bp open reading frame transcript encodes a protein of 1,777 amino acids, including an interrupted 1,502-residue collagenous domain and a 232-residue C-terminal non-collagenous domain. The expression pattern of this transcript is mainly found in the mantle and hemocytes. The recombinant protein corresponding α1(IV) C-terminal domain increased fibroblast proliferation by 69% and doubled collagen synthesis produced in primary cultures. This work provides the first complete primary structure of a mollusc non-fibrillar collagen chain and the biological effects of its C-terminal domain on human cells. In this study, we prove that the NC1 domain from a molluscan collagen can improve human fibroblast proliferation as well as differentiation.

Barx2 and Fgf10 regulate ocular glands branching morphogenesis by controlling extracellular matrix remodeling

The lacrimal gland (LG) develops through branching morphogenesis and produces secretions, including tears, that lubricate and protect the ocular surface. Despite the prevalence of LG disorders such as dry eye, relatively little is known about the regulation of LG development. In this study, we show that the homeobox transcription factor Barx2 is highly expressed in conjunctival epithelium, eyelids and ocular [lacrimal, harderian (HG), and meibomian (MG)] glands and is necessary for normal ocular gland and eyelid development. Barx2(-/-) mice show defective LG morphogenesis, absence of the HG, and defects in MG and eyelid fusion. Ex vivo antisense assays confirm the requirement for Barx2 in LG bud elongation and branching. Gene expression profiles reveal decreased expression of several adhesion and matrix remodeling molecules in Barx2(-/-) LGs. In culture, Barx2 regulates expression of matrix metalloproteinases (MMPs) and epithelial cell migration through the extracellular matrix. Fibroblast growth factors are crucial regulators of LG development and we show that Barx2 is required for Fgf10-induced LG bud elongation and that both Barx2 and Fgf10 cooperate in the regulation of MMPs. Together, these data suggest a mechanism for the effects of loss of Barx2 on ocular gland development. Intriguingly, salivary glands that also express a high level of Barx2 develop normally in Barx2(-/-) mice and do not show altered levels of MMPs. Thus, the function of Barx2 is specific to ocular gland development. Based on our data, we propose a functional network involving Barx2, Fgf10 and MMPs that plays an essential role in regulating branching morphogenesis of the ocular glands.

Mmp15 is a direct target of Snai1 during endothelial to mesenchymal transformation and endocardial cushion development

Cardiac valves originate from endocardial cushions (EC) formed by endothelial-to-mesenchymal transformation (EMT) during embryogenesis. The zinc-finger transcription factor Snai1 has previously been reported to be important for EMT during organogenesis, yet its role in early valve development has not been directly examined. In this study we show that Snai1 is highly expressed in endothelial, and newly transformed mesenchyme cells during EC development. Mice with targeted snai1 knockdown display hypocellular ECs at E10.5 associated with decreased expression of mesenchyme cell markers and downregulation of the matrix metalloproteinase (mmp) family member, mmp15. Snai1 overexpression studies in atrioventricular canal collagen I gel explants indicate that Snai1 is sufficient to promote mmp15 expression, cell transformation, and mesenchymal cell migration and invasion. However, treatment with the catalytically active form of MMP15 promotes cell motility, and not transformation. Further, we show that Snai1-mediated cell migration requires MMP activity, and caMMP15 treatment rescues attenuated migration defects observed in murine ECs following snai1 knockdown. Together, findings from this study reveal previously unappreciated mechanisms of Snai1 for the direct regulation of MMPs during EC development.

Transcriptional upregulation of MT2-MMP in response to hypoxia is promoted by HIF-1α in cancer cells

Hypoxia is a critical event in solid tumor development, invasion, and metastasis. Cellular adaptation to hypoxic microenvironment is essential for tumor progression and is largely mediated by hypoxia-inducible factor-1α (HIF-1α) through coordinated regulation of hypoxia-responsive genes. In this study, we found that membrane type-2 matrix metalloproteinase (MT2-MMP), one of the matrix metalloproteinase (MMP) family members, was a novel hypoxia-responsive gene and was upregulated by HIF-1α under hypoxia. When cancer cells were subjected to hypoxia (1% O(2) ) treatment, the mRNA and protein levels of MT2-MMP were significantly increased in a time-dependent manner in all three tested cancer cell lines including pancreatic cancer cells (PANC-1), nonsmall cell lung cancer cells (A-549), and cervix cancer cells (HeLa). Further analyses indicated that there were two hypoxia-responsive elements (HREs) in the MT2-MMP promoter, and HRE1 but not HRE2 was essential for MT2-MMP transcriptional activation under hypoxia. HIF-1α specifically and directly bound to MT2-MMP promoter was analyzed by HIF-1α binding/competition and chromatin immunoprecipitation (ChIP) assays. Furthermore, we found that upregulation of MT2-MMP under hypoxia could confer resistance to hypoxia-induced apoptosis and increase invasiveness of cancer cells. These findings provided a new insight into how cancer cells overcome hypoxic stress and trend to survive and invade, demonstrated a new regulatory mechanism of MT2-MMP expression in caner cells, and also revealed that MT2-MMP was a novel hypoxia-responsive gene and was upregulated by HIF-1α under hypoxia. © 2011 Wiley-Liss, Inc.

MT-MMPS as Regulators of Vessel Stability Associated with Angiogenesis

The development of vascular system depends on the coordinated activity of a number of distinct families of molecules including growth factors and their receptors, cell adhesion molecules, extracellular matrix (ECM) molecules, and proteolytic enzymes. Matrix metalloproteases (MMPs) are a family of ECM degrading enzymes required for both physiological and pathological angiogenesis. Increasing evidence, point to a direct role of membrane type-MMPs (MT-MMPs) in vascular system stabilization, maturation, and leakage. Our understanding of the nature of MT-MMP interaction with extracellular and cell surface molecules and their multiple roles in vessel walls and perivascular stroma may provide new insights into mechanisms underlying vascular cell–ECM interactions and cell fate decisions in pathological conditions. Regulation of vascular leakage by MT-MMP interactions with the ECM could also lead to novel targeting opportunities for drug delivery in tumor. This review will shed lights on the emerging roles of MT1-MMP and MT4-MMP in vascular system alterations associated with cancer progression.

Dynamics of salivary gland morphogenesis

Salivary glands form during embryonic development by a complex process that creates compact, highly organized secretory organs with functions essential for oral health. The architecture of these glands is generated by branching morphogenesis, revealed by recent research to involve unexpectedly dynamic cell motility and novel regulatory pathways. Numerous growth factors, extracellular matrix molecules, gene regulatory pathways, and mechanical forces contribute to salivary gland morphogenesis, but local gene regulation and morphological changes appear to play particularly notable roles. Here we review these recent advances and their potential application to salivary gland tissue engineering.

Distribution of α(IV) collagen chains in the ocular anterior segments of adult mice

The distribution of the collagen chains from α1(IV) to α6(IV) could serve as a basis for the characterization of type IV collagen. In this study, immunohistochemistry of the ocular anterior segment of adult mice was performed using specific monoclonal antibodies against each chain in the series from α1(IV) to α6(IV). The results show that the components of type IV collagen in vascular basement membranes are α1(IV) and α2(IV) with or without α5(IV) and α6(IV) chains and those in epithelium and muscle basement membranes are α1(IV), α2(IV), α5(IV), and α6(IV) chains. In corneal endothelium, pigmented epithelium of iris and ciliary body, and trabecular meshwork, α3(IV) and α4(IV) chains are also expressed in addition to α1(IV), α2(IV), α5(IV), and α6(IV) chains. Moreover, we investigated the change in molecular composition in ciliary body during postnatal development. α3(IV) and α4(IV) chains were also expressed in addition to α1(IV), α2(IV), α5(IV), and α6(IV) chains in ciliary pigmented epithelium basement membrane from 7 days after birth. This result suggests that the basement membranes gradually change their biochemical features owing to temporal regulation. Taken together, these findings suggest that the different distribution and the developmental expression of α1(IV) to α6(IV) chains are associated with the tissue-specific function of type IV collagen in basement membranes.

Mesenchymal miR-21 regulates branching morphogenesis in murine submandibular gland in vitro

Branching morphogenesis in murine submandibular glands (SMG) is regulated by growth factors, extracellular matrix (ECM) and many biological processes through interactions between the epithelium and the mesenchyme. MicroRNAs (miRNAs) are a set of small, non-protein-coding RNAs that regulate gene expression at the post-transcriptional level. We hypothesized that branching morphogenesis is partly regulated by miRNAs. Forty-four miRNAs and novel miRNA candidates were detected in SMG at embryonic day 13 by a cloning method combined with Argonaute-2 immunoprecipitation. MicroRNA21 (miR-21) expression in the mesenchyme was up-regulated and accelerated by epidermal growth factor, which is known to enhance branching morphogenesis in vitro. Down-regulation of miR-21 in the mesenchyme by locked nucleic acids was associated with a decrease in the number of epithelial buds. Relative quantification of candidates for target genes of miR-21 indicated that two messenger RNAs (for Reck and Pdcd4) were down-regulated in the mesenchyme, where miR-21 expression levels were up-regulated. These results suggest that branching morphogenesis is regulated by miR-21 through gene expression related to ECM degradation in the mesenchyme.

Branch formation during organ development

Invertebrates and vertebrates use branching morphogenesis to build epithelial trees to maximize the surface area of organs within a given volume. Several molecular regulators of branching have recently been discovered, a number of which are conserved across different organs and species. Signals that control branching at the cellular and tissue levels are also starting to emerge, and are rapidly unveiling the physical nature of branch development. Here we discuss the molecular, cellular, and physical processes that govern branch formation, and highlight the major outstanding questions in the field.

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.

Primary cellular meningeal defects cause neocortical dysplasia and dyslamination

OBJECTIVE

Cortical malformations are important causes of neurological morbidity, but in many cases their etiology is poorly understood. Mice with Foxc1 mutations have cellular defects in meningeal development. We use hypomorphic and null alleles of Foxc1 to study the effect of meningeal defects on neocortical organization.

METHODS

Embryos with loss of Foxc1 activity were generated using the hypomorphic Foxc1(hith) allele and the null Foxc1(lacZ) allele. Immunohistologic analysis was used to assess cerebral basement membrane integrity, marginal zone heterotopia formation, neuronal overmigration, meningeal defects, and changes in basement membrane composition. Dysplasia severity was quantified using 2 measures.

RESULTS

Cortical dysplasia resembling cobblestone cortex, with basement membrane breakdown and lamination defects, is seen in Foxc1 mutants. As Foxc1 activity was reduced, abnormalities in basement membrane integrity, heterotopia formation, neuronal overmigration, and meningeal development appeared earlier in gestation and were more severe. Surprisingly, the basement membrane appeared intact at early stages of development in the face of severe deficits in meningeal development. Prominent defects in basement membrane integrity appeared as development proceeded. Molecular analysis of basement membrane laminin subunits demonstrated that loss of the meninges led to changes in basement membrane composition.

INTERPRETATION

Cortical dysplasia can be caused by cellular defects in the meninges. The meninges are not required for basement membrane establishment but are needed for remodeling as the brain expands. Specific changes in basement membrane composition may contribute to subsequent breakdown. Our study raises the possibility that primary meningeal defects may cortical dysplasia in some cases.

Systems analysis of salivary gland development and disease

Branching morphogenesis is a crucial developmental process in which vertebrate organs generate extensive epithelial surface area while retaining a compact size. In the vertebrate submandibular salivary gland, branching morphogenesis is crucial for the generation of the large surface area necessary to produce sufficient saliva. However, in many salivary gland diseases, saliva-producing acinar cells are destroyed, resulting in dry mouth and secondary health conditions. Systems-based approaches can provide insights into understanding salivary gland development, function, and disease. The traditional approach to understanding these processes is the identification of molecular signals using reductionist approaches; we review current progress with such methods in understanding salivary gland development. Taking a more global approach, multiple groups are currently profiling the transcriptome, the proteome, and other 'omes' in both developing mouse tissues and in human patient samples. Computational methods have been successful in deciphering large data sets, and mathematical models are starting to make predictions regarding the contribution of molecules to the physical processes of morphogenesis and cellular function. A challenge for the future will be to establish comprehensive, publicly accessible salivary gland databases spanning the full range of genes and proteins; plans are underway to provide these resources to researchers in centralized repositories. The greatest challenge for the future will be to develop realistic models that integrate multiple types of data to both describe and predict embryonic development and disease pathogenesis.

Cell-matrix interactions in mammary gland development and breast cancer

The mammary gland is an organ that at once gives life to the young, but at the same time poses one of the greatest threats to the mother. Understanding how the tissue develops and functions is of pressing importance in determining how its control mechanisms break down in breast cancer. Here we argue that the interactions between mammary epithelial cells and their extracellular matrix (ECM) are crucial in the development and function of the tissue. Current strategies for treating breast cancer take advantage of our knowledge of the endocrine regulation of breast development, and the emerging role of stromal-epithelial interactions (Fig. 1). Focusing, in addition, on the microenvironmental influences that arise from cell-matrix interactions will open new opportunities for therapeutic intervention. We suggest that ultimately a three-pronged approach targeting endocrine, growth factor, and cell-matrix interactions will provide the best chance of curing the disease.

Parasympathetic innervation maintains epithelial progenitor cells during salivary organogenesis

The maintenance of a progenitor cell population as a reservoir of undifferentiated cells is required for organ development and regeneration. However, the mechanisms by which epithelial progenitor cells are maintained during organogenesis are poorly understood. We report that removal of the parasympathetic ganglion in mouse explant organ culture decreased the number and morphogenesis of keratin 5-positive epithelial progenitor cells. These effects were rescued with an acetylcholine analog. We demonstrate that acetylcholine signaling, via the muscarinic M1 receptor and epidermal growth factor receptor, increased epithelial morphogenesis and proliferation of the keratin 5-positive progenitor cells. Parasympathetic innervation maintained the epithelial progenitor cell population in an undifferentiated state, which was required for organogenesis. This mechanism for epithelial progenitor cell maintenance may be targeted for organ repair or regeneration.