Determining the Role of Extracellular Matrix Compliance on Facial Morphogenesis

We have previously found that collagen 4 and laminin are thinner in regions of the frontonasal process undergoing growth, suggesting tissue compliance may contribute to regulation of facial morphogenesis. Lysyl oxidase (LOX) initiates enzymatic crosslinking of collagen and elastin. Crosslinking in extracellular matrix fibrils increases tissue stiffness and may constrain growth in certain directions while allowing cells to exert forces required for directional growth. Our goal was to examine the distribution of lysyl oxidase in the frontonasal process (FNP) of chick embryos during growth and fusion of the palate. At Hamburger and Hamilton stage 22, LOX is present in the ectodermal basement membrane along the FNP, but at stage 26 it is present primarily in the basement membrane lining the nasal pits. LOX is also present in the lateral edges of the mesenchyme of the FNP at stage 22, but is more present in the medial and caudal mesenchyme at stage 26. These results mirror the distribution of collagen 4 and laminin, where more crosslinking was observed in regions resisting growth (like the nasal pits) and in regions where cellular forces may be generated to direct growth (ectodermal basement membrane). We next prevented initiation of crosslinking with a small‐molecule from Lathyrus odoratus , beta‐aminoproprionitrile (BAPN), which permanently binds to LOX. Ingestion of L. odoratus causes osteolathyrism, a musculoskeletal degenerative disease, and researchers have found that BAPN administered in high concentrations to embryos causes skeletal and craniofacial deformities. We found that microinjections of BAPN in the caudo‐lateral edge of the FNP at low concentrations (50, 75, and 100 ng/uL) caused mild truncation of the FNP without affecting LOX localization or increasing cell apoptosis (via TUNEL staining). Together, these results provide preliminary evidence that tissue compliance may play an important role in facial morphogenesis. Future work will utilize a LOX RNAi vector to further examine the role of extracellular matrix crosslinking on palate growth and fusion. Support or Funding Information Funding was provided by: CIHR, and NIH, NIDCR R21‐DE028198