FGF7 signals are relayed to autocrine EGF family growth factors to induce branching morphogenesis of mouse salivary epithelium

Abstract

Background: The Matrigel-embedded epithelium of the mouse submandibular gland undergoes branching morphogenesis when cultured in medium supplemented with fibroblast growth factor 7 (FGF7) and lysophosphatidic acid (LPA), whereas it elongates a stalk with limited branching in medium with only FGF7. Because LPA is a well-known activator of epidermal growth factor (EGF) signaling, we hypothesized the involvement of autocrine EGF family growth factors in the branching morphogenesis. Results: Reverse transcriptase polymerase chain reaction studies showed that three members, Tgfa, Hbegf,and Nrg1 of the EGF family were expressed in the epithelium cultured with FGF7 1 LPA as well as in the epithelium freshly isolated from the rudiments. All the growth factors induced extensive branching morphogenesis in the Matrigel-embedded epithelium in the presence of LPA. Tyrphostin AG112, an inhibitor of EGF signaling, severely impaired branching morphogenesis induced by FGF7 1 LPA without exogenous addition of EGF family growth factors to the culture medium. The shaking cultures, which were expected to decrease the concentration of autocrine growth factors near the epithelium by promoting their diffusion, significantly reduced branching morphogenesis induced by FGF7 1 LPA. Conclusions: Autocrine EGF family growth factors are involved in epithelial branching morphogenesis induced by FGF7 1 LPA. Developmental Dynamics 243:552-559,

Submandibular Parasympathetic Gangliogenesis Requires Sprouty-Dependent Wnt Signals from Epithelial Progenitors

“…Interestingly, inhibition of EGFR or PI3K decreased Wnt4 , Wnt5b , Wnt7b and Wnt10a suggesting that Wnt expression is positively regulated by PI3K downstream of erbB signaling (Figure 4C). To investigate the erbB regulation of Wnt expression in the epithelium, isolated epithelia were treated with FGF10, and three erbB ligands that are involved in SMG epithelial development (Kera et al, 2014; Miyazaki et al, 2004). Addition of HBEGF, Tgfα or Nrg1 alone shows that that they rapidly increase Wnt4 , Wnt5b and Wnt10a expression within 4 h (Figure 4D).…”

Regulatory mechanisms of branching morphogenesis in mouse submandibular gland rudiments

“…The same research group also showed that EGF supports branching morphogenesis of SMG rudiments, especially cleft formation, and that fibroblast growth factor 7 (FGF7) is needed for stalk elongation of SMG epithelium [22] . The EGF system, including members of its ligand family such as EGF, TGF-α, HB-EGF and neureglin-1 (NRG1), and members of its receptor family such as EGFR (ErbB1), ErbB2 and ErbB3 [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , is one of the important regulators of branching morphogenesis of SMG rudiments. Moreover, the ligand family members activate and phosphorylate the ErbB receptor family proteins in the plasma membrane.…”

The contribution of specific cell subpopulations to submandibular salivary gland branching morphogenesis

“…The mechanisms through which clefts initiate remain unclear but mesenchymally-induced activation of autocrine EGF signaling in the epithelium appears to promote cleft initiation [26], and lysophosphatidic acid (LPA) can synergize with EGF [27] (Figure 2). Semaphorin 3A/3C acting through the neuropilin receptor 1 (Nrp1) [28] may also be involved.…”

“…Recent studies are revealing a complex cross-talk between the molecular effectors. For example, mesenchymal FGFs and LPA cooperatively promote SMG epithelial branching via FGF-driven autocrine EGF signaling [26] (Figure 3). Upstream of FGFs, platelet-derived growth factors (PDGFs) have been implicated in the regulation of FGF signaling in salivary gland branching, and PDGF AA and BB regulate FGF expression by the neural crest-derived mesenchyme [61].…”