Food digestion by cathepsin L and digestion-related rapid cell differentiation in shrimp hepatopancreas

Cathepsin L (CatL) has been readily localized in the large vacuole and in the apical complex of the digestive B-cell of the shrimp hepatopancreas. Immunogold technique revealed the occurrence of CatL in zymogen granule, digestive body and digestive vacuole of the B-cell in the hepatopancreas of Metapenaeus ensis. Coalescences of zymogen granule with sub-apical vacuole, and of two small digestive bodies were observed. This progressive coalescence of CatL vesicles is direct evidence of involvement of CatL in intracellular digestion. Released CatL vesicles and free CatL were found in the lumen of hepatopancreatic tubule. CatL mRNA existed in F-cell, but not in the mature B-cell. This finding supports the previous suggestion that F-cell is the precursor of B-cell. F-cell is a transient form. Transition from F-cell to B-cell is fast. We define F-cell as the transcribing cell, F/B-cell as the enzyme-synthesizing cell and B-cell as the enzyme-secreting cell. For the first time, we suggest that R-cell is the replacing cell for the leaving B-cell. CatL degrades nutrient intracellularly and extracellularly. The most interesting finding is that CatL is transcribed in one type of cell, and the very cell evolves quickly to a morphologically different cell where the enzyme functions.