Molecular cloning and genetic ontogeny of some key lipolytic enzymes in large yellow croaker larvae (Larimichthys crocea R.)

Abstract

This study was conducted to investigate the genetic ontogeny of some key lipolytic enzymes in large yellow croaker Larimichthys crocea larvae. Partial cDNA sequences of bile activated lipase (BAL) and pancreatic enzyme secretory phospholipase A2 group IB (sPLA2 IB) were cloned and characterized. Real-time quantitative PCR (RT q-PCR) was conducted from 1 day after hatching (DAH) to 40 DAH in larvae fed the following sequence: rotifers, Artemia nauplii, copepods and then frozen copepods. In this study, 1181 bp and 205 bp partial cDNA sequences were cloned for BAL and sPLA2 IB respectively. The mRNA of all lipolytic enzymes were already present before mouth opening. The mRNA expression of BAL and sPLA2 IB during larval development showed a similar pattern: both of them increased gradually from 1 DAH to 25 DAH, followed by a slight decrease up to 40 DAH. The mRNA expression of lipoprotein lipase (LPL) also increased first and then decreased, peaked at 20 DAH. However, the mRNA expression of hepatic lipase (HL) increased constantly up to 40 DAH. These results suggest that the transcript levels of these enzymes were mainly regulated by age in early stage and by the exogenous diet in late stage of large yellow croaker larvae. Energy available for fish larvae, originating from lipid oxidation, may have been reduced as indicated by decreasing expression of LPL due to lower lipid levels in frozen copepods compared to fresh copepods. Besides, lipid hydrolysis for utilization in the liver of large yellow croaker larvae from chylomicron-remnant, very low density lipoprotein (VLDL)-remnant and high density lipoprotein increased along larval development of large yellow croaker which was reflected by the increasing concentration of HL mRNA.