Hagfish Cartilage

Summary

Morphological, biochemical, molecular biological and biomechanical analysis of cartilages from the Atlantic hagfish, Myxine glutinosa, reveal they are unusual tissues. At least three different cartilages designated Types 1, 2 and 3 have been identified.

Type 1 appears superficially to resemble other vertebrate cartilages; however, ultra-structural analysis reveals that the extracellular matrix (ECM) is non-collagenous. Type 2 bears no morphological resemblance to any known vertebrate cartilage, Type 3 is similar in appearance to Type 1; however, biochemical analysis of Types 1 and 3 cartilages reveal that each is composed primarily of a cyanogen bromide (CNBr) insoluble protein of unique composition. Myxinin, the principle structural protein of Type 1 cartilage, is similar but not identical to lamprin, the main structural protein of lamprey annular cartilage. The major structural protein of Type 3 cartilage has a composition very different from myxinin and as yet has not been named. The CNBr insoluble material from Type 2 cartilage is a minor component with a composition different from myxinin, Type 3 cartilage and lamprin.

Molecular biological studies suggest no homology between hagfish and lamprey cartilages. Comparative biomechanical studies indicate that the modulus of elasticity of hagfish cartilage is about one order of magnitude higher than lamprey and bovine cartilages.

The morphological and biochemical differences between hagfish and lamprey cartilages support the concept that these two agnathans followed long independent evolutionary histories.