Extracellular Matrix Composition Is Altered Alongside Dysmorphology in the Developing Palate

Abstract

Normal morphogenesis of the primary palate involves directed outgrowth of the facial primordia until they meet and fuse. Gradients of cellular proliferation induced by growth factors are the current paradigm for directed outgrowth, but active cellular migration and physical force propagated through the extracellular matrix (ECM) likely also direct growth. Previously we showed that two of the main components of the ECM, collagen IV and laminin, are thinner in regions of the frontonasal process (FNP) undergoing growth, suggesting tissue stiffness may passively constrain growth in certain directions. We have also shown that increasing Fibroblast growth factor (FGF) signaling in the FNP of chick embryos prior to palate fusion caused overgrowth and disrupted cellular organization. Since cells form and modify the ECM, and since the ECM is required for cellular organization and movement, the effects of FGF signaling on morphogenesis may be due in part to active feedback between ECM and cells. Our goal was to examine the changes to the ECM in the FNP following alteration of FGF signaling. Blocking FGF signaling with SU5402 caused hypoplasia of the FNP and increased the concentration of collagen IV and laminin in regions of expected outgrowth. Conversely, increasing FGF signaling with exogenous FGF2 caused overgrowth of the FNP and decreased concentration of the ECM components. Analysis using transmission electron microscopy of the FGF2 treated samples suggests increasing FGF signaling also decreases the thickness of the epithelium and basement membrane. These results provide preliminary evidence that ECM may play an important role in facial morphogenesis, and that FGF signaling may affect an active biomechanical feedback system between cells and ECM. In the future I will further characterize ECM composition and compliance across the FNP using Fourier transform infrared spectroscopy and atomic force microscopy to generate 3-dimensional maps of biomechanical properties in the face. I will also use confocal microscopy to map cellular organization across the face. I will overlay these maps onto representative reconstructions of the face to correlate regional variation in biomechanical properties and cellular organization with dysmorphologies that occur following exogenous modulation of FGF signaling.