Eccles, L. E. | Search bioRxiv

bioRxiv2025

Evolution of highly repetitive silk genes in the Luna moth, Actias luna

Gene duplications are a major driver of molecular diversification and phenotypic evolution. Arthropod silk genes provide an excellent model for studying these processes due to their highly repetitive sequences and rapid evolutionary rates. In Lepidoptera, the Fibroin heavy chain (fibH) gene encodes the primary structural protein for silk fibers, contributing largely to their mechanical strength. This inner fibroin core is surrounded by an outer coating composed primarily of sericins. Sericins are a group of highly repetitive, serine-rich proteins that modulate silk fiber properties. Although sericins in the Domesticated silkworm (Bombyx mori) have been associated with life stage-specific variation in silk characteristics, their evolution and function across Lepidoptera remain poorly understood. Here, we provide a detailed molecular characterization of sericin genes in the Luna moth (Actias luna), a saturniid species known for forming dense, robust, silk-woven cocoons. We identified eight sericin genes that (1) are frequently arranged into clusters of closely related paralogs, (2) exhibit considerable variation in repeat number and amino acid composition, and (3) display distinct gene expression patterns across life stages. A comparison of sericin genes across Saturniidae and Bombycidae reveals evidence for convergent subfunctionalization. These findings suggest that sericin gene duplications enable dynamic shifts in silk composition both within and between species, potentially reflecting adaptive responses to ecological and functional demands. Significance StatementGene duplications are thought to be a major driver of molecular diversification and phenotypic evolution. Arthropod silk genes, characterized by their repetitive sequences and rapid evolution, provide an ideal model for studying these processes. Sericins, a group of highly repetitive, serine-rich silk proteins, are hypothesized to have contributed to the diversification of silk properties, both within and across lepidopteran species. However, their diversity and evolution is poorly understood. Focusing on the Luna moth (Actias luna), we show that sericin gene duplications across Saturniidae have led to subfunctionalization, enabling changes to silk composition. These modifications may represent adaptative responses to ecological and functional demands.

evolutionary biology↗

bioRxiv2025

Regionalization of gene expression and cell types in the silk gland of the pantry moth Plodia interpunctella

Lepidopteran silk glands include a posterior silk gland (PSG) that secretes core fibers and a middle silk gland (MSG) that secretes adhesive sericins. While well-studied in the silkworm (Bombyx mori), little is known about the gene expression profiles underlying the diversity of lepidopteran silks. Here we characterized the silk gland from the pantry moth Plodia interpunctella using a combination of quantitative and spatial assays. RNA-seq analyses of differential gene expression between the MSG and PSG depict the transcriptomic divergence between these two secretory tissues. In the PSG, high expression of fibroin genes FibL and FibH were detected, whereas MSG samples were dominated by transcripts encoding major sericins-- bioadhesive proteins that form the coating of the silk fiber. Hybridization Chain Reaction (HCR) mRNA profiling revealed sharp cellular boundaries within the silk gland: PSG cells exclusively expressed fibroins, while MSG comprised two compartments each expressing different combinations of sericins. Our findings corroborate the conserved organization of lepidopteran silk glands into specialized secretory subdivisions, and establish Plodia as a promising comparative model for studying silk diversity. This work provides a foundation for future research into the cellular and evolutionary basis of silk production across Lepidoptera.

genomics↗