Histochemical Localization Of Cathepsin L In Sea Cucumber (Stichopus Japonicus) Body Wall

Sea cucumber is a kind of marine animal that has the strong ability of autolysis. It coulddegrade itself when expose to external stimulus. The phenomenon, termed autolysis, will leadto softening of the body, which deteriorates the eating quality and causes economic losses. Inthe present study, the autolysis of sea cucumber（Stichopus japonicus）was induced by UVirradiation. The tissue changes involved with autolysis in sea cucumber were investigatedthrough light microscopic examination of tissues by H&E staining. Meanwhile, anenzyme-histochemical method for localization of cathepsin L in sea cucumber body wall wasestablished by using Z-Phe-Arg-4MβNA·HCl as a substrate. Based on the histochemicalmethod, the tissue distribution of cathepsin L in fresh and autolytic sea cucumber body wallwas investigated. At the same time，the change of activity of cathepsin L was also tested.Through this research, the relationship between autolysis degree and distribution of cathepsinL was revealed, which contributes to further understand the autolysis mechanism and controlautolysis.For fresh sea cucumber, the cuticle was intact, the epithelial cells arranged orderly, andthe connective tissues seemed orderly and uniform. After autolysis, the cuticle was damagedgradually, or even disappeared, the epithelial cells distributed irregularly, the fiber networkstructure of loose layer became thinner, and the fiber network structure of compact layerbecame blurred. In summary, the autolytic phenomenon of compact layer was less obviousthan that of cuticle, epithelium tissue and loose layer.The distribution of cathepsin L in sea cucumber body wall was investigated by usingenzyme-histochemical method. Results showed that distribution of cathepsin L was notuniform. The distribution of cathepsin L was dense in epithelium tissue and loose layer, butwas relatively sparse in compact layer. During autolysis, the staining spots in epitheliumtissue and dermis layer became spread, even disappeared. This maybe because the enzyme hasbeen released from cells or organelles and diffused in tissue, resulted in the low concentration in local tissue.At the beginning of autolysis time, the activity of cathepsin L increased, andthen, it declined, but without big change.In summary, the more dense distribution of cathepsin L, the more obvious autolysisappeared. The positive correlation between them indicated that cathepsin L may take part inthe autolysis. The localization of cathepsin L was concentrated in the tissue before autolysisand released after stimulus, which may result in the degradation of extracellular matrix.