Developmental regulation of gastric pepsin and pancreatic serine protease in larvae of the euryhaline teleost, Oreochromis mossambicus

Most recent research on teleost digestive enzymes has focused on the immunohistochemistry of flounder and catfish, fewer studies have been done of gene expression. The present study is made an attempt to clarify the expression of digestive enzymes in tilapia (Oreochromis mossambicus) during larval development. This work was done by cloning the digestive enzymes, semi-quantifying the expression of genes by RT-PCR-Southern blot, detecting the expression of proteins (western blot) and investigating enzymatic activity. Under microscopic observation, the mouths of tilapia larvae were seen to open on the third day after hatching and on the fifth day after hatching, the actinotrichia were reabsorbed and the larvae began feeding. The partial nucleotide sequences of pepsinogen, trypsinogen and chymotrypsinogen were obtained. After RT-PCR and southern blotting analysis, the expressing pattern of pepsinogen mRNA appeared on day 2 after hatching, while mRNAs of trypsinogen and chymotrypsinogen were both detected 1 day after hatching. The proteins of larval pepsin, trypsin and chymotrypsin appeared 1 day after hatching, and specific activities of these enzymes were detectable on day 3 (for pepsin) and day 5 (for trypsin and chymotrypsin) after hatching. The transcription of the genes for these three digestive enzymes gradually increased after hatching and that all protein detected on day 1, suggesting that all proteins may result from maternal sources.