Morphological and compositional basis of silk fiber function in Actias luna

Abstract

Silk is a highly versatile natural protein fiber with a wide range of uses, yet its diversity in composition and function remains poorly understood across the tree-of-life. This study investigates the silk of the Luna moth, Actias luna (Saturniidae), known to produce high-density cocoons with distinct fiber characteristics. Despite the broad recognition of A. luna as an important species for research and education, its silk production, silk fiber composition, and properties remain under characterized, particularly in comparison to other Saturniidae and model insect species such as Bombyx mori. Building from the recently assembled A. luna genome, this study examines key repeat motifs and the amino acid composition of the silk fibroin heavy chain (FibH) in relation to silk fiber properties across species. We demonstrate that A. luna silk is similar to other saturniid silks, aligning with established trends that link fiber characteristics to structural protein composition. Analyses of fiber characteristics were further expanded to silk fibers produced by A. luna at different developmental stages. The variation in fiber morphology and composition across larval instars suggests that life stage-specific silk fiber uses may stem from differences in protein expression. These findings advance understanding of how evolutionary and developmental shifts influence silk fiber properties, providing a foundation for rational design of protein-based biomaterials with tunable mechanical and structural characteristics for biomedical applications.