Comparative Analysis of the Integument Transcriptomes between Stick Mutant and Wild-Type Silkworms

Area of Science:

• Entomology
• Molecular Biology
• Biochemistry

Background:

• Insect integument provides structural support and protection.
• Mutations affecting integument properties can alter insect morphology, behavior, and survival.
• The stick (sk) silkworm mutant exhibits a less flexible, stick-like larval body.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the stiff exoskeleton of the stick (sk) silkworm mutant.
• To identify differentially expressed genes and pathways in the sk mutant's integument.
• To analyze the mechanical properties of the sk mutant's cuticle.

Main Methods:

• Mechanical property analysis of larval cuticles.
• Transcriptome sequencing of wild-type and sk mutant larvae.
• Differential gene expression analysis.
• Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses.

Main Results:

• The sk mutant cuticle showed higher storage modulus and lower loss tangent, indicating increased stiffness.
• Transcriptome analysis revealed significant differences in gene expression, with 710 upregulated and 1009 downregulated genes in the sk mutant.
• Upregulated genes included chitin-binding peritrophin A domain genes and a chitinase; downregulated genes included other chitin-binding genes, a trehalase, and antimicrobial peptides.
• KEGG analysis highlighted enrichment in fructose and mannose metabolism and tyrosine metabolism pathways.

Conclusions:

• The stiff exoskeleton of the sk mutant is associated with altered expression of genes involved in chitin metabolism and structural components.
• Changes in metabolic pathways, specifically fructose/mannose and tyrosine metabolism, may contribute to the mutant's phenotype.
• This study provides a molecular basis for understanding the development of a stiffened insect exoskeleton.