Identification of Novel Tissue-specific Proteins in the Suboesophageal Body of the Silkworm, Bombyx mori

抄録

The suboesophageal body (SB) of the silkworm, Bombyx mori, has been known for a long time, but its function has not been clarified. This study demonstrates that SB produces lysozyme, a tissue-specific chymotrypsin inhibitor (SCI-SB) and a P27K ortholog of a glycoprotein known from another moth. The nucleotide sequences of SCI-SB and P27K cDNAs were newly determined and that of the lysozyme was confirmed to be identical to the previous data. The amount of lysozyme in SB is enhanced during molting and rises profoundly in larvae challenged with a bacterial injection. Lysozyme was shown to be released into haemolymph but could not be detected in other tissues. By contrast, the P27K protein, which is 56.5% identical with a haemolymph glycoprotein of Manduca sexta, occurs in B. mori in all analyzed tissues except the silk glands. Its function is unknown. SCI-SB belongs to the Kunitz-type proteinase inhibitors and exhibits 87.1, 85.5 and 85.7% homologies with chymotrypsin inhibitors SCI-I, SCI-II and SCI-III, respectively, which are known from silkworm haemolymph. However, SCI-SB is expressed exclusively in SB. The nature and expression patterns of identified proteins indicate that SB is an immunity-associated organ.