Characterization of silk gland expression across two caddisfly species using long-read sequencing technology

Trichoptera, the most diverse order of aquatic insects, modify their environment using aquatic silk production. They use silk in a wide variety of ways, including fixed retreats, capture nets, silk cases, and pupal cocoons. The suborder Annulipalpia includes the fixed retreat-makers, which mostly construct capture nets and fixed retreats using silk. Members of the suborder Integripalpia predominantly construct portable cases or are free-living, often integrating various materials from aquatic environments. Trichoptera silk is synthesized in modified salivary glands through the expression of several genes. Among the genes linked to silk production, Heavy- and Light-chain (H- and L-) fibroin constitute most of the silk fiber core. Most studies examining Trichoptera silk have primarily focused on H-fibroin, but a complete understanding of silk diversity requires identifying the majority of genes involved in its production. Isoform sequencing presents an opportunity to obtain full-length or near-full length transcripts of genes expressed in the silk organ and to examine transcript diversity. We collected late-instar larvae of Arctopsyche grandis, a fixed-retreat maker, and Rhyacophila brunneai, a cocoon-maker, in mountain streams in north-central Utah, USA. Their silk glands were dissected, and RNA was extracted using a Trizol method and sequenced using IsoSeq sequencing on a PacBio Revio instrument. Iso-Seq raw reads were pre-processed and non-redundant transcripts were annotated to characterize gene expression in the silk glands across the two caddisfly species.