Identification of FGF10 Targets in the Embryonic Lung Epithelium during Bud Morphogenesis

Abstract

Genetic studies implicate Fgf10-Fgfr2 signaling as a critical regulator of bud morphogenesis in the embryo. However, little is known about the transcriptional targets of Fgf10 during this process. Here we identified global changes in gene expression in lung epithelial explants undergoing FGF10-mediated budding in the absence of other growth factors and mesenchyme. Targets were confirmed by their localization at sites where endogenous Fgf10 signaling is active in embryonic lungs and by demonstrating their induction in intact lungs in response to local application of FGF10 protein. We show that the initial stages of budding are characterized by marked up-regulation of genes associated with cell rearrangement and cell migration, inflammatory process, and lipid metabolism but not cell proliferation. We also found that some genes implicated in tumor invasion and metastatic behavior are epithelial targets of Fgf10 in the lung and other developing organs that depend on Fgf10-Fgfr2 signaling to properly form. Our approach identifies Fgf10 targets that are common to multiple biological processes and provides insights into potential mechanisms by which Fgf signaling regulates epithelial cell behavior.Signaling by fibroblast growth factor 10 (Fgf10) 1 and its receptor Fgfr2b is critical for bud morphogenesis in many developing structures. During organogenesis, Fgf10 is expressed by the mesoderm from where it diffuses to activate Fgfr2b in adjacent endodermal or ectodermal-derived cells and induce budding (1). Disruption of Fgf10-Fgfr2b signaling is lethal at birth and results in multiple organ defects. Abnormalities in Fgf10-or Fgfr2b-deficient mice include agenesis of the anterior pituitary gland, lung, thyroid, salivary gland, and limb and dysgenesis of inner ear, teeth, skin, pancreas, kidney, palate, and hair follicles (2-5). Fgf10 expression is also required for adipocyte differentiation and wound healing (6 -8).In the developing respiratory tract of the mouse, Fgf10 is first detected at embryonic (E) day 9.5 during primary bud formation. Subsequently, during branching morphogenesis (E10.5-16.5), Fgf10 is dynamically expressed in the distal lung mesenchyme at the prospective sites of budding (9, 10). The spatial and temporal distribution of Fgf10 is essential for patterning of lung epithelial tubules.Bud morphogenesis involves major changes in cytoskeletal organization, cell adhesion, migration, invasion, and proliferation among other activities. Little is known about the targets of Fgf10-Fgfr2b signaling in the lung epithelium when buds are forming. Although gene expression in the developing lung has been characterized by several reports, most studies were performed in the intact organ. Using whole lungs to identify targets that result primarily from Fgf10-Fgfr2b activation is difficult, because in the mesoderm, Fgf10 is present with several other endogenous signals such as Wnts, hepatocyte growth factor, or epidermal growth factor.Previous studies have shown that recombinant FGF10 is able to support bud morphogenesi...

Localized Fgf10 expression is not required for lung branching morphogenesis but prevents differentiation of epithelial progenitors

“…Fgf10 has been shown to regulate epithelial β-catenin signaling during lung development as well as in the adult lung (Lü et al, 2005;Ramasamy et al, 2007;Volckaert et al, 2011). We therefore examined the status of epithelial Wnt/β-catenin signaling in lungs overexpressing Fgf10.…”

“…β-Catenin is not only a downstream transcriptional target of epithelial Fgf10 signaling (Lü et al, 2005), but increasing data also indicate that Fgf10 is able to increase nuclear β-catenin directly, via phosphorylation of β-catenin on Ser552 and inhibition of Gsk3β, through the PI3K/AKT pathway (He et al, 2007;Ramasamy et al, 2007;Volckaert et al, 2011). In addition, FGF signaling via Erk/MAPK phosphorylates the Wnt co-receptor Lrp6 on Ser1490 and Thr1572 and phosphorylates β-catenin directly on Tyr142, thereby releasing it from cadherin complexes (Krejci et al, 2012).…”

Generation of multiciliated cells in functional airway epithelia from human induced pluripotent stem cells

“…BMP4 and fibroblast growth factor (FGF) are known to act downstream of Wnt3a and are involved in the differentiation and maintenance of the distal lung epithelium (13). FGF10 is expressed in the lung mesenchyme and is a critical regulator of endoderm proliferation and lung bud morphogenesis (14,15). FGF7 [also known as keratinocyte growth factor (KGF)] can also be detected early in lung development and is known to interact with other factors to regulate epithelial branching and epithelial proliferation (16,17).…”

Fgf10-positive cells represent a progenitor cell population during lung development and postnatally

“…During early lung development, Fgf10 is expressed in the distal (submesothelial) mesenchyme and it acts on the opposite epithelium expressing Fgfr2b to maintain the epithelial cells in a progenitor-like state and induce branching and migration (Bellusci et al, 1997;Lü et al, 2005;Park et al, 1998). Gain of function of Fgf10 during Fgf10-positive cells represent a progenitor cell population during lung development and postnatally development leads to epithelial progenitor state arrest and distalization of the lung (Nyeng et al, 2008;Volckaert et al, 2013), whereas loss of function of Fgf10 results in branching simplification and decreased numbers of epithelial progenitors.…”