Gut-specific expression of cathepsin L and B in amphioxus Branchiostoma belcheri tsingtauense larvae

Cathepsin L and B are involved in yolk processing during oocyte maturation and embryogenesis in most invertebrates and vertebrates. Here we examine the developmental expression of cephalochordate amphioxus cathepsin L (AmphiCL) and cathepsin B (AmphiCB) in the adult and developing embryos and larvae. In situ hybridization of adult amphioxus demonstrated that both AmphiCL and AmphiCB transcripts were strongly expressed in the hepatic caecum and hind-gut besides expression at various levels in other tissues examined. Whole mount in situ hybridization and RT-PCR techniques revealed that AmphiCL and AmphiCB transcripts appeared in the primitive gut in 2-day and 1-day larvae, respectively. However, no signals were detected in the early embryos or larvae. Parallel experiments were performed measuring AmphiCL and AmphiCB activities in the mature oocytes and developing embryos and larvae. Albeit both enzymes were present in the mature oocytes, their roles in yolk protein processing remain to be clarified. In accordance with gene expression patterns, AmphiCL and AmphiCB activities were only detectable in the 2-day larvae, rather than in younger stages, suggesting that both AmphiCL and AmphiCB are implicated in the development of gut, and inferring no roles for yolk processing during embryogenesis in amphioxus Branchiostoma belcheri tsingtauense.