The Penaeus monodon Chitinase 1 Gene Is Differentially Expressed in the Hepatopancreas During the Molt Cycle

We have isolated a full-length chitinase complementary DNA from the tiger shrimp Penaeus monodon that encodes a 621 amino acid protein possessing the functional domains of the chitinase protein family. The Penaeus monodon chitinase 1 (PmChi-1) gene product is 81.8% identical to a chitinase 1 protein expressed in the hepatopancreas of Penaeus japonicus. Analysis by reverse transcription-polymerase chain reaction (RT-PCR) indicates that PmChi-1 messenger RNA is detectable in the hepatopancreas and the gut. PmChi-1 expression during the molt cycle fluctuates markedly, with lowest mRNA levels at stages A(1), C, and D(3); there is a dramatic increase in transcript abundance at the D(2) stage. Using the same tissues and molt stages, RT-PCR analyses of genes encoding other digestive enzymes (trypsin, chymotrypsin, and cathepsin L), a muscle structural protein (tropomyosin II), and housekeeping proteins (elongation factor II and GTP-binding protein) indicate that PmChi-1 is expressed in a distinct tissue-specific and stage-specific manner. The other digestive enzyme genes are expressed in a similar spatiotemporal pattern, but none exhibited a dramatic increase in transcript abundance at stage D(2). Increased expression of PmChi-1 at D(2) suggests that hepatopancreas-expressed chitinase is involved in the degradation of endogenous chitin in the gut peritrophic membrane prior to molting.