High Expression Levels of the Genes cyclin-A2 and glucocorticoid receptor Are Associated with High-Quality Embryos in Gilthead Sea Bream (Sparus aurata L.)

Abstract

Identifying early egg-quality predictors is a major challenge in finfish hatcheries, and relevant research is now focused on the development of molecular markers. In our study, we examined whether fertilization rates and early morphological abnormalities in sea bream egg batches of high (HQ) and low quality (LQ) are associated with mRNA levels of cathepsin D, cathepsin Z, cyclin-A2, and glucocorticoid receptor. Additionally, we examined whether these early quality descriptors were associated with the development of skeletal abnormalities during the larval period. HQ egg batches were characterized by significantly higher rates of normal embryos (95.8 ± 2.3%) and lower rates of unfertilized (2.8 ± 1.0%) and abnormal eggs (1.3 ± 1.4%), compared to LQ (84.2 ± 0.8% normal embryos, 12.3 ± 12.3 unfertilized eggs, and 3.5 ± 1.4% abnormal eggs) (p < 0.05, Mann–Whitney U test). Relative expression of cyclin-A2 and glucocorticoid receptor was found to be significantly higher in HQ embryos compared to those of LQ (respectively, p < 0.01 and p < 0.05, Mann–Whitney U test). No statistically significant differences were observed in the mRNA transcripts of cathepsin D and cathepsin Z (p > 0.05, Mann–Whitney U test). Differences in the rate of skeletal abnormalities between the two quality groups of larvae were not significant (p > 0.05, G-test), indicating that cyclin-A2 and glucocorticoid receptor may serve as reliable molecular markers for early prediction of fish egg quality but not for later larval stages.