A family of non-collagen-based cartilages in the skeleton of the sea lamprey, Petromyzon marinus

Cartilage structures of the sea lamprey, Petromyzon marimus, have previously been reported to stain by the Verhoeff method for elastin and to have a morphology similar to that of elastic cartilage of higher vertebrates. Earlier we showed that lamprin, the major matrix protein of lamprey annular cartilage, although not identical to elastin, cross-reacted with antibodies to elastin and shared significant sequence and structural similarities. Here we demonstrate that the majority of the skeletal cartilage of the lamprey is noncollagenous in character, remaining intact after treatment of the tissues with cyanogen bromide. However, unlike annular and neurocranial cartilages, which consist mainly of lamprin, evidence from amino acid compositions, immunohistochemistry, and western and northern blotting indicates that the major matrix protein of branchial and pericardial cartilage is not lamprin, but a second cyanogen bromide-insoluble protein or group of proteins with similarities to elastin. These results suggest that the skeletal cartilage of lower vertebrates consists of a family of noncollagenous, elastin-like proteins. The relationships among members of this family of cartilaginous proteins and between these proteins and vertebrate elastins, and the implications of these relationships for understanding the evolutionary lineage of elastin will await further characterization of these proteins. (C) 1997 Elsevier Science Inc.