Expression pattern of two collagen type 2 alpha1 genes in the Japanese inshore hagfish (Eptatretus burgeri) with special reference to the evolution of cartilaginous tissue.

Collagen type 2 alpha1 (Col2A1) protein is a major component of the cartilaginous extracellular matrix (ECM) in vertebrates. Over the past two decades, the evolutionary origin of Col2A1 has been studied at the biochemical and molecular levels in extant jawless vertebrates (hagfishes and lampreys). Although these studies have contributed to our understanding of ECM protein evolution, the expression profile of the Col2A1 gene in hagfishes has not been fully described. We have performed molecular cloning and analyzed the gene expression pattern of the Col2A1 gene in the Japanese inshore hagfish (Eptatretus burgeri). We succeeded in isolating two Col2A1 genes, EbCol2A1A and EbCol2A1B, in which EbCol2A1A was expressed in the noncartilaginous connective tissues whereas EbCol2A1B was detected in some cartilaginous elements. Based on these results, we discuss the evolutionary history of Col2A1 genes in early vertebrates.