Ectodysplasin A regulates the development of scale and intermuscular bone in teleosts

Most bony fish are extensively covered by scales, which play crucial roles in locomotion, balance, and sensory perception. However, the molecular mechanisms underlying fish scales development remain poorly understood. In this study, comparative genomic analyses were performed between scaled and scaleless fish species, leading to the identification of key genes (eda, wnt3a, gsk3bb, etc.) involved in scale formation. Phylogenetic and sequence analyses of the eda gene revealed that the Eda protein in Monopterus albus lacks a transmembrane domain, disrupting Eda/Edar binding and potentially driving scale degeneration. Using CRISPR/Cas9 technology, we generated zebrafish eda^-/- mutants, which exhibited a complete absence of scales, fin rays, pharyngeal teeth, and gill rakers. Notably, the intermuscular bones in these mutants showed significantly reduced length, and simplified morphology, indicating impaired growth. Furthermore, quantitative PCR (qPCR) analysis demonstrated that eda deficiency disrupts the Eda/Edar/NF-κB signaling pathway. Our findings provide significant insights into the molecular regulatory mechanisms underlying the development of skin appendages (e.g., scales) and intermuscular bones.