Stage-Specific Expression of Lens-Associated Structural Genes During Early Embryogenesis in European Seabass (Dicentrarchus labrax)

Background/Objectives: Lens development is an essential component of visual-system development during fish embryogenesis, yet its transcriptional timing remains poorly characterized in European seabass (Dicentrarchus labrax). This study aimed to provide a stage-resolved transcriptomic characterization of lens-associated gene expression in D. labrax embryos and to relate these patterns to classical embryological stages. Methods: Publicly available RNA-seq data from embryos at the mid-gastrula, late somitogenesis, and hatching stages were analyzed. A targeted lens-associated gene set was defined using Gene Ontology annotations, with emphasis on genes assigned to the structural constituent of the eye lens category. Expression patterns were examined using normalized counts, variance-stabilized data, principal component analysis, and pairwise differential expression analysis. Results: Lens-associated genes displayed clear stage-dependent expression dynamics. Principal component analysis separated samples primarily by developmental stage, with the first two components explaining 89.3% of the total variance. The strongest biological shift occurred between mid-gastrula and late somitogenesis, when transcripts encoding β-crystallins and lens-fiber architecture components increased markedly. Among the most pronounced changes were the induction of crybb1l3 and cryba4, along with increased expression of membrane and cytoskeletal genes, such as the lim2 paralogs and bfsp1. By hatching, this structural-gene expression pattern was partly maintained, while specific crystallin-related loci, including crybg1a, showed further stage-associated increases. Conclusions: These findings define stage-specific patterns of lens-associated gene expression in D. labrax embryos and indicate that lens-associated structural gene expression is most pronounced during late somitogenesis among the stages analyzed. This work provides a useful reference for future studies of visual development in European seabass and for aquaculture-oriented investigations of early sensory ontogeny.