Cuticular chitin synthase and chitinase mRNA of whiteleg shrimp Litopenaeus vannamei during the molting cycle

Cuticular chitin synthase and chitinase mRNA of whiteleg shrimp Litopenaeus vannamei during the molting cycle a b s t r a c t a r t i c l e i n f o Chitin metabolism is of high relevance for shrimp growth because it has to be synthesized and cleaved in each molt. We studied chitin synthase and chitinase mRNAs from whiteleg shrimp Litopenaeus vannamei. For this, cDNA coding for cuticular chitin synthase (LvChS) and chitinase isoenzymes (LvChi1, LvChi2 and LvChi3) was amplified, sequenced and identified. In a qualitative analysis, LvChi1 and LvChi3 were detected only in the he-patopancreas and are probably involved in digestion of food chitin. LvChi2 transcript was found in pleopods, uropods, gills, eyestalk, and digestive tube; LvChi2 is likely to be involved in the hydrolysis of chitin from the exoskeleton and peritrophic membrane, but not in food chitin digestion. LvChS was found widely distributed in the organism, including the hepatopancreas. Thus, it seems to be involved in synthesis of chitin to build the exoskeleton and also the peritrophic membrane. Relative expression of LvChS and LvChi2 genes was evaluated by quantitative RT-PCR in the integument. These transcripts had a varying pattern of abundance during the molt cycle, based on the need of shrimp to synthesize or hydrolyze chitin from exoskeleton. Chitin is a linear homopolymer of β-linked N-acetylglucosamine (NAcGlc) that occurs widely in nature. World annual bioproduction of chitin was estimated at 100 × 10 9 t, being an important source of carbon for heterotrophic bacteria (Cauchie, 2002; Tharanathan and Kittur, 2003). Chitinous structures are found in several taxa as well as the cell wall of fungi (Roncero, 2002), egg shells of nematodes (Brydon et al., 1987) and exoskeleton and peritrophic matrix of insects (Merzendorfer and Zimoch, 2003) and crustaceans (Roer and Dillaman, 1984). Thus, the study of chitin metabolism is of biotechnological, ecological , and physiological relevance. The exoskeleton of crustaceans is a four-layered matrix that confers support, rigidity, and impermeability to the body. Chitin is present in the inner three layers, forming a sclerotized complex with structural proteins and calcium salts (O'Brien et al., 1991). For crustaceans to grow, the rigid exoskeleton has to be discarded by hydrolysis of cuticular components and a new exoskeleton has to be synthesized to match the new body size (Promwikorn et al., 2004). The process of synthesizing a new exoskeleton and discarding the old one (ecdysis or molting) …