Characterization of primary structure of the major silk gene,h-fibroin, across caddisfly suborders (Trichoptera)

Abstract

Similar to their sister order Lepidoptera (moths and butterflies), the primarily aquatic larvae of Trichoptera (caddisflies) produce silk, which is used to build a wide variety of underwater architectures, such as cocoons, fixed retreats, and tube-cases. This diverse silk usage allows them to exploit a wide range of aquatic environments. Studies of the long and highly repetitive major silk gene, heavy chain fibroin (h-fibroin), are rare due to difficulties in sequence assembly. Only recently, new long-read sequencing techniques have been used to assemble high-quality, full-length sequences of this gene. Here, we report seven new gene and protein sequences of h-fibroin covering the breadth of the order Trichoptera, including the three major life history strategies characterized by different silk usage (fixed retreat-, cocoon- and tube case-making). When comparing the primary structure of the h-fibroin, we find conserved patterns, but also substantial diversity across groups. The signatures of conservation, such as conservation of N- and C-termini and characteristic repeating structural modules, suggest a common mechanism of silk formation and similar material properties across all three groups. The diversity in the number and order of the repeating modules, as well as the increasing structural complexity of h-fibroin in fixed retreat and tube-case building compared to cocoon-builders, may reflect differences in mechanical properties related to the diversity of silken architectures. This study presents a basis for future research into the role of fibroins in caddisfly silk function as a gauge of the potential of underwater silk in material applications.

Chromosome-scale genome assemblies of Himalopsyche anomala and Eubasilissa splendida (Insecta: Trichoptera)

“…The GC content of H. anomala and E. splendida assemblies was 31.55% and 32.76%, respectively. Notably, the estimated genome size closely matched the assembly size, with the genome assembly size of H. anomala resembling that of other Himalopsyche species 27,28 , whereas the genome size of E. splendida exceeded that of Eubasilissa regina (440.07 Mb) 29 . Genome completeness was assessed using Benchmarking Universal Single-Copy Orthologs (BUSCO) v3.0.2 30 , employing the parameter "-m genome", during each stage of the assembly.…”

Evolution of Opsin Genes in Caddisflies (Insecta: Trichoptera)

“…Presumably, such varied environments and wing colorations require a plastic and diverse visual system. To gain an understanding of opsin evolution in caddisflies, we analyzed the occurrence and phylogenetic relationships of opsin genes across 25 caddisfly genomes, including five newly assembled genomes and 20 publicly available genome assemblies (Frandsen et al, 2019;Frandsen et al, 2023;Heckenhauer et al, 2019;Heckenhauer et al, 2022;Heckenhauer et al, 2023;Kawahara et al, 2022;Luo et al, 2018;Olsen et al, 2021;Ríos-Touma et al, 2021, The Darwin Tree of Life Project Consortium, 2022, representing the major evolutionary lineages within the order.…”