Expression patterns of tyrosinase, peroxidase and alkaline phosphatase genes during larval shell formation of the mollusk Haliotis discus hannai

To elucidate the mechanisms underlying larval shell development, this study examined the morphological traits of shell field in the Pacific abalone Haliotis discus hannai using scanning electron microscopy and assessed the expression profiles of five candidate genes related to shell formation, including tyrosinases gene (Hdi-Tyr1, Hdi-Tyr2), peroxidases gene (Hdi-Prx1, Hdi-Prx2), and alkaline phosphatase gene (Hdi-Alp). The results revealed that the shell field consisted of at least three distinct cell populations displaying a characteristic "rosette" pattern. Expression of the Hdi-Tyr1 and Hdi-Tyr2 displayed U-shaped patterns in the shell field of trochophore larvae, and their mRNA were identified in columnar cells at the mantle edge of veliger larvae. However, Hdi-Alp, Hdi-Prx1 and Hdi-Prx2 were exclusively expressed in the prototroch and head of the larvae and showed no detectable expression in the shell field. These findings indicate that Hdi-Tyr1 and Hdi-Tyr2 may be involved in the larval shell formation of H. discus hannai, whereas Hdi-Prx1, Hdi-Prx2 and Hdi-Alp are not involved in this process. These insights provide a foundation for subsequent research into the shell development mechanisms and genetic improvement of shell-related traits in mollusks.