Accumulation of collagen III at the cleft points of developing mouse submandibular epithelium

Increased type III/I collagen and alpha 1(I)/alpha 2(I) chain in a bronchopulmonary dysplastic lung

The type ratio of collagen III/I and molecule ratio of alpha 1(I)/alpha 2(I) were analysed in lungs from five infants with bronchopulmonary dysplasia (BPD) and seven control infants. All five BPD lungs showed typical characteristics, with pulmonary fibrosis and irregular cystic formation at postmortem examination. A pepsin digestion technique followed by interrupted gel electrophoresis was performed for the determination and molecular analysis of collagens III and I. The ratio of collagen types III and I were significantly increased in BPD lung (P < 0.005). The ratio of alpha 1(I) and alpha 2(I) were also significantly increased in BPD lung (P < 0.05). It is likely that collagen III is predominantly increased and that the alpha 1(I) trimer is formed in the active stage of BPD lungs.

An extracellular matrix infrastructure provides support for murine secondary palatal shelf remodelling

A crucial part of secondary palate morphogenesis is the movement of the palatal shelves from an initial vertical position on either side of the tongue to a final horizontal one above it to achieve palate closure. The immunocytochemical localization of extracellular matrix (ECM) molecules in the palatal shelf during this remodelling and reorientation revealed the existence of an ECM infrastructure within the mesenchyme. The major components of this infrastructure were collagen III, fibronectin, and hyaluronate (HA). With remodelling, HA's domain within the mesenchyme was expanded, whereas those of fibronectin and collagen III became more circumscribed. The expansion of an HA-rich matrix within the mesenchyme is thought to be crucial for palatal reorientation. The results of this study suggest that, as this expansion occurs, it is modulated by collagen and fibronectin components of the ECM infrastructure. Prior to shelf remodelling, this infrastructure may be anchored by a specialized region of the midoral epithelial-mesenchymal interface and the subjacent mesenchyme which is characterized by the unique distribution of collagen III, fibronectin, and tenascin. The midoral palatal epithelium also may play a role in directing shelf expansion. This epithelial region undergoes changes in cell packing and epithelial cell layering that correlate with shelf remodelling. These changes occur concomitantly with changes in the expression of collagen III, collagen IV, and laminin within the underlying basement membrane. The localization and patterning of tenascin within the developing palate suggests that it not only contributes to the postulated anchoring structure of the midoral epithelial-mesenchymal region, but also plays a role in the determining the fate of the medial edge epithelial cells during the final stage of palate closure.

Localization of extracellular matrix components in developing mouse salivary glands by confocal microscopy

The importance of the extracellular matrix (ECM) in epithelial-mesenchymal interactions in developing organisms is well established. Proteoglycans and interstitial collagens are required for the growth, morphogenesis, and differentiation of epithelial organs and the distribution of these molecules has been described. However, much less is known about other ECM macromolecules in developing epithelial organs. We used confocal microscopy to examine the distribution of laminin, heparan sulfate (BM-1) proteoglycan, fibronectin, and collagen types I, IV, and V, in mouse embryonic salivary glands. Organ rudiments were isolated from gestational day 13 mouse embryos and cultured for 24, 48, or 72 hours. Whole mounts were stained by indirect immunofluorescence and then examined using a Zeiss Laser Scan Microscope. We found that each ECM component examined had a distinct distribution and that the distribution of some molecules varied with culture time. Laminin was mainly restricted to the basement membrane. BM-1 proteoglycan was concentrated in the basement membrane and also formed a fine network throughout the mesenchyme. Type IV collagen was mainly located in the basement membrane of the epithelium, but it was also present throughout the mesenchyme. Type V collagen was distributed throughout the mesenchyme at 24 hours, but at 48 hours was principally located in the basement membrane. Type I collagen was distributed throughout the mesenchyme at all culture times, and accumulated in the clefts and particularly at the epithelial-mesenchymal interface as time in culture increased. Fibronectin was observed throughout the mesenchyme at all times.

Growth and branching morphogenesis of rat collecting duct anlagen in the absence of metanephrogenic mesenchyme

The growth and differentiation of the epithelium in many tissues is mediated by interactions with the adjacent mesenchyme, but the mechanisms responsible remain undefined. To identify the factors involved in the growth and branching morphogenesis of ureteric bud, which is the collecting duct anlagen, buds from 13-gestation-day rat embryos were separated from the metanephrogenic mesenchyme and explanted to culture dishes coated with gelled type I collagen in a defined medium. Under these conditions buds attached to the substrate and grew out without indication of cell senescence. When buds were instead suspended in gelled type I collagen, branching morphogenesis was observed despite the absence of mesenchyme although it was not as extensive as in vivo. Since growth occurred much more slowly in culture than expected, culture conditions were varied in attempts to accelerate the process. Despite extensive screening of matrices and growth factors, only epidermal and endothelial cell growth factors stimulated growth to a significant extent. Transforming growth factor-beta, on the other hand, was a potent inhibitor of growth. Homogenates from tumors that caricature metanephrogenic mesenchyme were highly mitogenic for bud cells and, thus, will be a source of material for characterizing regulatory factors involved in renal growth. These studies show that growth and branching morphogenesis of the ureteric bud can occur without direct cell-cell interactions with the metanephrogenic mesenchyme and that matrices and factors secreted by the mesenchyme may mediated these activities in vivo.

Epithelial-mesenchymal interactions in the development of salivary glands

The full expression of both morphogenesis and secretory cell differentiation in salivary glands is modulated or controlled, at least in part, by interactions between the salivary epithelium and the surrounding mesenchyme. Salivary gland morphogenesis and cytodifferentiation are partially linked but independently regulated processes. This presentation reviews the information that establishes the role of various extracellular matrix molecules and direct epithelial-mesenchymal interactions in the induction, control, and maintenance of morphogenesis and secretory cell differentiation in salivary glands.

The role of extracellular matrix in the morphogenesis and differentiation of salivary glands

The processes of morphogenesis and cytodifferentiation are partially linked, independently regulated processes. The full expression of both processes is modulated or controlled, at least in part, by components of the extracellular matrix. This paper reviews the body of work that demonstrates a role for epithelial-mesenchymal interactions and various extracellular matrix molecules in the induction, control, and maintenance of salivary gland morphogenesis and cytodifferentiation. In addition, new, preliminary information which further elucidates the role of laminin and type IV collagen in the processes of morphogenesis and cytodifferentiation is presented. With regard to the role of extracellular matrix molecules in the regulation of salivary gland morphogenesis and cytodifferentiation, it appears that types I, III, and IV collagen, laminin, and chondroitin sulfate proteoglycan play roles in the control of glandular morphogenesis. With the exception of type IV collagen, these molecules do not appear to be involved in the regulation of cytodifferentiation of salivary gland secretory cells. On the other hand, of the extracellular matrix molecules tested so far, only type IV collagen appears to play a role in the regulation of salivary gland secretory cell differentiation.

Transforming growth factor betas in mammalian embryogenesis

Type beta transforming growth factors (TGF beta s) are members of a large superfamily of related proteins, each of which plays a pivotal role in embryonic processes. The TGF beta s per se are at least five in number, though only three isoforms have been identified in mammals. Here we will review the evidence, taken from in vitro studies on bioactivity and histochemical localization of RNAs and encoded proteins in vivo, that TGF beta 1, beta 2 and beta 3 are involved in several mammalian developmental processes, including control of growth, differentiation, tissue inductions and morphogenesis.

Epithelial shape change in mouse embryonic submandibular gland: modulation by extracellular matrix components

Early morphogenesis of mouse submandibular gland provides an excellent model for the formation of epithelial lobules as a consequence of epithelial-mesenchymal interactions. Both proteoglycans and a glycosaminoglycan, high molecular weight components which contain amino-sugars and hexuronic acids, seem to be important in maintaining the lobular structure through the formation of epithelial basal lamina. Collagen also appears to play a crucial role in this morphogenesis. By visualizing the distribution of collagen fibrils and by changing the concentration of collagen in the gland, we have developed a new hypothesis which emphasizes the mechanical role of mesenchyme in epithelial cleft formation. Precise mechanisms for the involvement of these molecules have not been elucidated, yet it is now clear that knowledge of the function of the extracellular matrix components is a prerequisite for understanding the epithelial-mesenchymal interactions.