Evolution of Collagen and Structural Proteins

Molecular evidence indicates that collagen IV, a structural protein enabling basement membrane formation, emerged in metazoan ancestors approximately 600 million years ago. Collagen IV allowed cells to adhere in organized layers, creating the scaffolding for multicellular epithelial tissues. Studies of ctenophores and sponges reveal that these organisms carry collagen IV genes homologous to those in complex animals, while unicellular sister-groups lack them entirely. This protein innovation enabled the transition from single-celled life to organisms with differentiated tissues and body plans.