Life stage-specific expression of sericin genes of Actias luna (Lepidoptera: Saturniidae)

Silk proteins from Lepidoptera are gaining interest for various applications such as biomedicine, cosmetics, and textiles. Among these proteins are fibroins and sericins, the two most abundant proteins in Lepidopteran silk. Fibroin is an insoluble protein forming the inner core of the silk fiber, while sericins make up the outer protective coat of the fiber. Specifically, sericins – named after the abundance of serine residues within – function like a soluble protein glue that binds fibroin filaments together, contributing to the structural integrity and protective nature of the cocoon. The expression patterns of sericins were studied extensively in the Domestic Silkworm (Bombyx mori). In this species, different sericins are expressed at different life stages, and these differential expression patterns are linked to different silk properties observed in larval silk and cocoon silk. However, data on the expression of sericins in wild silk moths (Lepidoptera: Saturniidae) is more limited, especially for the iconic Luna Moth (Actias luna). This moth species is distributed across the eastern half of North America, and uses its silk to spin cocoons in its final instar, and generate a pad to anchor its old cuticle during ecdysis in earlier instars. Hence, our study investigated the expression patterns of sericin genes across Luna Moth instars. We designed species-specific primers and conducted qPCR based on RNA extracted from dissected silk glands across larval instars. Our qPCR data represents one of the most in-depth analyses of silk gene expression across life stages, and demonstrates its variable expression across time.