Abstract: Carboxylesterase is a multifunctional superfamily. To determine the function of carboxylesterase in different tissues of Bombyx mori, we cloned a carboxylesterase gene named BmCarE-9 (GenBank accession no. EU523534) from B. mori by using rapid amplification of cDNA ends (RACE) and reverse transcription polymerase chain reaction (RT-PCR) methods. BmCarE-9 contains a 1 680 bp open reading frame (ORF), which encodes 559 amino acids. This cDNA-deduced protein BmCarE-9 has a predicted molecular weight (MW) of 64.2 kD, and isoelectric point (pI) of 7.13. Structure analysis showed that BmCarE-9 has a similar catalytic triad in which two residues have changed. We investigated the developmental expression patterns of BmCarE-9 in different tissues of the Day-3 5th instar larvae and in silk glands of different day-old 5th instar larvae by real-time quantitative PCR. The results showed that BmCarE-9 was expressed specifically in silk glands at high levels, and mainly expressed in the median and posterior silk glands. Furthermore, the expression of BmCarE-9 increased as silk glands developed, and decreased at the end of 5th instar stage. It is so inferred that BmCarE-9 might be involved in the development of silk glands or the synthesis of silk proteins.

Key words: Bombyx mori, BmCarE-9, silk gland, real-time quantitative PCR, tissue expression