MOLECULAR CLONING OF TRYPSIN AND THE EFFECT OF DIETARY PROTEIN LEVELS AND STARVATION ON TRYPSIN mRNA EXPRESSION AND ENZYME ACTIVITY IN JUVENILE CHINESE SUCKER (MYXOCYPRINUS ASIATICUS BLEEKER)

The effect of dietary protein and starvation on the expression of trypsin was evaluated in the Chinese sucker (Myxocyprinus asiaticus Bleeker). The complete trypsin cDNA was cloned from juvenile Chinese sucker pancreatic tissue by using RACE and PCR methods. We used semi-quantitative RT-PCR and enzymatic activity measurements to quantify mRNA expression and trypsin activity in fish that were either starved or fed differing levels of dietary casein (35%, 45% and 55%). The results showed that the Chinese sucker trypsin cDNA sequence was 912 bp in length. Trypsin activity and mRNA levels were higher in fish that were fed moderate (45% casein) levels of protein than those that were fed high or low levels. Starvation significantly decreased mRNA expression level and trypsin activity. The changes in trypsin activity tended to lag behind the changes in mRNA levels. There was no direct relationship between the trypsin activity and mRNA level. Given this, the trypsin synthesis is a complex process regulated by a balance of several factors in the Chinese sucker.