Meeting Abstract
Gene duplication is one of the driving forces of evolution. In the most cases, one of the duplicated genes is subsequently lost, but in some cases, the gene diverges and acquires a new function. The latter phenomenon is called neofunctionalization. At a time of hatching of teleost, the embryos secrete enzyme(s) to digest their egg envelopes. The enzymes are named hatching enzyme. In the evolution of teleost, the hatching was originally performed by a single type of hatching enzyme. The enzyme swells and softens egg envelope, and embryos ruptured the softened egg envelope by their movement. In the early stage of teleost evolution, the gene duplication and neofunctionalization has occurred. The euteleost fishes, the most diverged group of teleost, possess the duplicated two hatching enzymes genes, HCE (high choriolytic enzyme) and LCE (low choriolytic enzyme). HCE has kept the activity of ancestral enzyme, swelling the egg envelope, and LCE acquired new function, solubilization of the swollen egg envelope by cleaving two specific sites on egg envelope proteins. We are interested in the mechanism of neofunctionalization. In this study, we tried to identify the key amino acid residues for neofunctionalization of medaka Oryzias latipes HCE and LCE using mutant recombinant (rec.) hatching enzymes. As the result, the rec. HCE substituted 4 amino acid residues to LCE-type residues acquired the LCE-like cleavage activity, and lost the original HCE activity. Conversely, the rec. LCE with the 4 amino acid substitutions to HCE-type residues acquired the HCE-like cleavage activity, and lost the original LCE activity.
