Quantification of shape and cell polarity reveals a novel mechanism underlying malformations resulting from related FGF mutations during facial morphogenesis

Abstract

Fibroblast growth factor (FGF) signaling mutations are a frequent contributor to craniofacial malformations includingmidfacialanomaliesandcraniosynostosis. FGFsignalinghasbeenshowntocontrol cellularmechanisms that contribute to facialmorphogenesis and growth such as proliferation, survival,migration and differentiation. We hypothesized that FGF signaling not only controls themagnitude of growth during facialmorphogenesis but also regulates the direction of growth via cell polarity. To test this idea, we infected migrating neural crest cells of chicken embryos with replication-competent avian sarcoma virus expressing either FgfR2C278F, a receptormutation found inCrouzon syndromeor the ligand Fgf8. Treated embryos exhibited craniofacialmalformations resemblingfacialdysmorphologiesincraniosynostosissyndrome. Consistentwithourhypothesis,ectopicactivationof FGF signaling resulted in decreased cellproliferation, increased expression of the Sprouty class ofFGF signaling inhibitors, andrepressedphosphorylationofERK/MAPK. Furthermore,quantificationofcellpolarity in facialmesenchymal cells showed that while orientation of the Golgi body matches the direction of facial prominence outgrowth in normal cells, in FGF-treated embryos this direction is randomized, consistent with aberrant growth thatweobserved. Together, thesedatademonstrate thatFGFsignalingregulates cellproliferationandcellpolarity and that these cell processes contribute to facialmorphogenesis. © The Author 2013.