Fibronectin requirement in branching morphogenesis

Abstract

Many organs, including salivary glands, lung and kidney, are formed during embryonic development by epithelial branching. In branching morphogenesis, repetitive epithelial cleft and bud formation create the complex three-dimensional branching structures characteristic of many organs. Although the mechanisms are poorly understood, one might involve the site-specific accumulation of some regulatory protein. Here we show that the extracellular matrix protein fibronectin is essential for cleft formation during the initiation of epithelial branching. Fibronectin messenger RNA and fibrils appeared transiently and focally in forming cleft regions of submandibular salivary-gland epithelia, accompanied by an adjacent loss of cadherin localization. Decreasing the fibronectin concentration by using small interfering RNA and inhibition by anti-fibronectin or anti-integrin antibodies blocked cleft formation and branching. Exogenous fibronectin accelerated cleft formation and branching. Similar effects of fibronectin suppression and augmentation were observed in developing lung and kidney. Mechanistic studies revealed that fibrillar fibronectin can induce cell-matrix adhesions on cultured human salivary epithelial cells with a local loss of cadherins at cell-cell junctions. Thus, fibronectin expression is required for cleft formation in branching morphogenesis associated with the conversion of cell-cell adhesions to cell-matrix adhesions.

Toll‐like receptor signaling inhibits structural development of the distal fetal mouse lung

“…We hypothesized that LPS might disrupt similar processes in the fetal lung during distal development. Fibronectin mediates cell adhesion and spreading and is required for branching morphogenesis in the submandibular gland and during development of proximal conducting airways (Sakai et al, 2003). We, therefore, tested if fibronectin was also required for distal lung branching and if LPS could alter its expression.…”

Efficient ultrafiltration‐based protocol to deplete extracellular vesicles from fetal bovine serum

“…The UF filter used in this study retains proteins larger than 100 kDa, allowing smaller proteins to pass into the filtrate. This is likely to enable cell growth and potentially extracellular matrix production (ECM) by the cells [29,30]. However, it has been reported that the lack of large molecules, such as glycoproteins, may have adverse effects on cell differentiation and proliferation [31].…”

Salivary Gland Branching Morphogenesis — Recent Progress and Future Opportunities

“…The ECM protein fibronectin has also been identified as a putative cleft initiator (Sakai et al , 2003). It accumulates in the clefts and appears to direct its own inward translocation deeper into the cleft as cleft progression occurs (Larsen et al , 2006).…”

“…Consistent with the possibility that E-cadherin functions in place of other junctional proteins to stabilize external epithelial surfaces, the localization of E-cadherin is considerably stronger between cell junctions of outer bud epithelial cells than those between the inner bud cells (Walker et al, 2008). However, when a cleft forms to interrupt this layer of outer epithelial cells, E-cadherin localization and expression diminish as cell shift from cell-cell to cell-matrix adhesion (Sakai et al, 2003). …”