Ctenophore mesoglea: building a mucus-like body
Ctenophora are one of the earliest, if not the earliest branching animal, making them crucial for insight into the early events of metazoan evolution. Ctenophores are largely composed of an extracellular mesoglea, but they lack homologs for the fibrous collagens that form a typical metazoan extracellular matrix (ECM). Therefore, the nature of this body-dominating material and its physiological role remains unknown. We found that ctenophore mesoglea is dominated by mucin-related proteins and novel sulfated polysaccharides. Mucus-like material that functions as an internal skeleton rather than as an external secretion indicates fundamental differences in epithelial function and ECM physiology between ctenophores and other Metazoa, suggesting an early period of biochemical and biomechanical diversity prior to the innovation of elastic connective tissue.