The circadian transcriptome of marine fish (Sparus aurata) larvae: synchrony matters

Trabajo presentado en el 18th International Symposium on Fish Nutrition and Feeding (ISFNF. 40 years of research in fish nutrition), celebrado en Las Palmas de Gran Canaria del 3 al 7 de junio de 2018.Growth and health in farmed fish may rely on the synchronization among endogenous rhythms, which are affected by feeding and other clues imposed by production practices. It is known that activity of nutrient-sensitive clock proteins impacts nutrient and energy utilization in other animals. Thus, we hypothesized that the metabolism of fish larvae has a synchronized time-based organization to allow timely nutrient metabolism and fast growth. To test this hypothesis, a high-density oligonucleotide microarray was used to examine the daily expression of 13,939 unique genes in whole gilthead sea bream (Sparus aurata) larvae kept under a light/dark cycle with continuous feed availability. Up to 2,229 genes were differentially expressed, and the first two components of Principal Component Analysis explained more than 81% of the total variance. Clustering analysis of differentially expressed genes identified 4 major clusters that were triggered sequentially, with a maximum expression at 0 h, 3 h, 9-15 h and 18-21 h zeitgeber time. Various core clock genes (per1, per2, per3, bmal1, cry1, cry2, clock) were identified in clusters 1-3, and their expression was correlated with several genes in each cluster. Functional analysis of these clusters revealed a consecutive activation of molecular pathways related to phototransduction, intermediary metabolism, development, chromatin remodeling, and cell cycle regulation. This circadian synchrony of key biological processes in fish larvae can be used as an indicator of larvae quality. This can be the basis of new molecular tools for evaluating larvae rearing protocols, the efficacy of nutritional interventions and for larvae batches certification. As several sampling points are not practical under aquaculture operations, we propose the use of a single sampling point to assess the expression of subsets of genes from antiphase clusters to find algorithm indicators of synchrony. Alternatively, expression ratios of candidate genes at two different times may be informative about the scope of processes such as neuromuscular development and oxidative capacity, which are also considered highly informative of larval growth and later performance of juvenile fish. Such approaches can contribute to improve the quality of farmed fish providing new criteria and insights for fish quality certification.N