Quantification of gene transcription and enzyme activity for functionally important proteolytic enzymes during early...

Gene transcripts and enzyme activities were quantified for a selection of functionally important aminopeptidases at 2-day intervals throughout the first 72 days of development in the Pacific oyster Crassostrea gigas. Leucine aminopeptidase (LAP) and cathepsin B (CathB) gene transcripts were quantified using fluorogenic ('real time') PCR. LAP and CathB gene transcripts were detected at all time points. The proportion of CathB transcripts remained essentially constant and low throughout development (Ct<35). The proportion of LAP transcripts was often similar (Ct<30), but with a distinct peak in transcript abundance at day 19 (Ct approximately 23). CathB and cathepsin D (CathD) enzyme activities were measured biochemically. Whilst CathD activity peaked at day 19, LAP and CathB activities both peaked at day 24. The closely coupled increase in transcript and enzyme activity for LAP indicates regulation at the transcriptional level. Alternatively, the peak in enzyme activity for CathB without enhanced transcriptional activity suggests post-transcriptional regulation. Similar mechanisms of regulation for LAP and CathB have been observed in both plants and mammals, indicating widespread conservation.