Downstream Branches of the Fibroblast Growth Factor Signaling Pathway Act Interdependently to Shape the Face

• Published in: The FASEB journal 2022-05, Vol.36 (S1), p.n/a
• Main Authors: Hanne, Nicholas J., Hu, Diane, Allen, Charlie, Shakir, Bilal, Liu, Wei, Hallgrímsson, Benedikt, Marcucio, Ralph
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2022.36.S1.L7907

The musculoskeletal tissues of the head develop from primordia, composed of neural crest cells, that evaginate and fuse to form the structures of the face. This occurs through a complex process controlled not only by regional differences in cellular proliferation, apoptosis, and differentiation, but also directed cellular migration and oriented cellular behavior. Disruption of normal development of the facial primordia can either prevent apposition and fusion of craniofacial primordia, leading to malformations such as cleft lip and/or palate. Previously, we found that stimulating signaling by fibroblast growth factor (FGF) in neural crest cells of chick embryos slowed proximodistal expansion of the facial primordia and widened the midface. Activation of the FGF pathway decreased cell proliferation in the frontonasal process (FNP) and disrupted cellular orientation, which were correlated with shape of the FNP. Blocking FGF signaling with a chemical inhibitor caused severe truncation of the FNP and decreased proliferation. Our previous results confirm that FGF signaling affects craniofacial morphogenesis, seemingly by altering multiple cellular functions. FGF receptors are receptor tyrosine kinases which utilize many common downstream signaling cascades that direct cellular proliferation, apoptosis, differentiation, migration, and oriented cell behaviors, but it is not clear which downstream pathway explains our previous results. In this study we used chemical inhibitors to block three pathways downstream of FGF receptor activation to determine their effect on facial morphology and cellular activity in the FNP of the chick embryo. Blocking MAPK, PLCγ, and PI3K pathways individually caused similar mild truncations of proximo‐distal growth in the FNP over 24 and 72 hours, and similar reductions in cellular proliferation. Cellular orientation was not significantly affected by any treatment. Blocking all three downstream pathways together caused a more severe proximo‐distal truncation of growth of the FNP, but not as severe as blocking Fgf signaling entirely. These results suggest that the downstream branches of the FGF pathway act inter‐dependently and in a non‐linear fashion to shape the face. Soon we will measure cellular orientation in the inhibitor cocktail treated FNPs and quantify the changes in FNP shape using three‐dimensional geometric morphometrics.