A truncated form of fibronectin is expressed in fish and mammals.

Fibronectin is a highly conserved and well-characterized extracellular matrix protein that plays a crucial role in many cellular processes. In amphibians, birds and mammals, multiple isoforms of fibronectin are generated by differential RNA splicing at three exons. Previously, we identified a novel form of fibronectin (FN2) in zebrafish that possesses a truncated structure and is generated by a unique RNA splicing pattern. Unlike other fibronectins, FN2 exists as a monomer and localizes on the cell surface. Here we show that this novel fibronectin is evolutionarily conserved, found in multiple species of fish and in mice and humans. The unusual structure, unique cellular distribution and conserved pattern of expression indicate that FN2 may have a novel function in normal cellular processes.