Fibronectin assembly during early embryo development: A versatile communication system between cells and tissues

Background: Fibronectin extracellular matrix is essential for embryogenesis. Its assembly is a cell‐mediated process where secreted fibronectin dimers bind to integrin receptors on receiving cells, which actively assemble fibronectin into a fibrillar matrix. During development, paracrine communication between tissues is crucial for coordinating morphogenesis, typically being mediated by growth factors and their receptors. Recent reports of situations where fibronectin is produced by one tissue and assembled by another, with implications on tissue morphogenesis, suggest that fibronectin assembly may also be a paracrine communication event in certain contexts. Results: Here we addressed which tissues express fibronectin (Fn1) while also localizing assembled fibronectin matrix and determining the mRNA expression and/or protein distribution pattern of integrins α5 and αV, α chains of the major fibronectin assembly receptors, during early chick and mouse development. We found evidence supporting a paracrine system in fibronectin matrix assembly in several tissues, including immature mesenchymal tissues, components of central and peripheral nervous system and developing muscle. Conclusions: Thus, similarly to growth factor signaling, fibronectin matrix assembly during early development can be both autocrine and paracrine. We therefore propose that it be considered a cell–cell communication event at the same level and significance as growth factor signaling during embryogenesis. Developmental Dynamics 245:520–535, 2016. © 2015 Wiley Periodicals, Inc. Key Findings We characterized the dynamics of expression vs. localization of fibronectin and its major assembly receptors. Fibronectin is often expressed in a tissue and assembled by another, thus having a paracrine system of assembly in certain contexts. This paracrine system may be important to coordinate morphogenesis between tissues. This system may also be a way for a tissue to orchestrate the development of another.