Early Placenta Insulin-Like Peptide (INSL4) belongs to the insulin family. INSL4 is expressed in the early placental cytotrophoblast and syncytiotrophoblast INSL4 is a secreted protein and a precursor that undergoes post-translational cleavage to produce 3 polypeptide chains, A-C, that form tertiary structures composed of either all three chains, or just the A and B chains. INSL4 plays an important role in the development of trophoblast and in the regulation of bone formation.