Characterization of candidate genes involved in growth of black tiger shrimp Penaeus monodon

The optic lobe of the female-shrimp eyestalk was selected as the target tissue for suppressive subtractive hybridization (SSH) because it is a place for synthesis of many hormones and peptides/enzymes involved in molting and growth. SSH was performed to screen genes differentially expressed in the optic lobe between large female (LF; body weight > 90 percentile of weight distribution curve) and small female (SF; body weight < 10 percentile). A total of 426 recombinant clones were obtained from the two directions. After sequencing and analysis less than 30% of the resulting expressed sequence tag (EST) exhibited high homology to known records at GenBank (BlastX with E-value < 10− 4) indicating little available molecular information on the optic lobe. Among the EST with relatively high homology to GenBank records, 5 candidate ESTs had homology to records for genes involved in cell differentiation/proliferation, cell cycle and hormone processing. These included genes resembling cyclophilin, cyclophilin A, fibrillarin, SPARC and PC2. These candidate ESTs were selected to confirm the reproducibility of the SSH data using semi-quantitative RT-PCR normalized with EF-1α. Pearson's correlation analysis confirmed that the index of relative cyclophilin, SPARC and fibrillarin-like expression was negatively correlated with body weight (p < 0.05) and this supported the SSH data indicating their low relative expression in LF shrimp when compared to SF shrimp. The index of relative cyclophilin-like expression showed the highest correlation coefficient with body weight (r = − 0.678). The relationship could be expressed by inverse fitted equation: body weight (g) = 38.243/(index of relative cyclophilin-like expression). This fitted inverse model could predict the body weight of female shrimp with 91.6 % coefficient of determination (R2) based on the index of relative cyclophilin-like expression in the optic lobe of female P. monodon.