Transcriptome analysis reveals the gene expression changes in Strongyloides ratti tissue-migrating larvae

Strongyloides ratti is an intestinal nematode commonly found in rats. Unlike other Strongyloides species, the tissue-migrating third-stage larvae in S. ratti follow a unique route of invasion via the nasofrontal region before reaching the gut. Despite its importance in host invasion, the transcriptomic profile of this larval stage has not been characterized. In this study, we performed RNA sequencing (RNA-seq) to examine gene expression in head-derived tissue-migrating third-stage larvae (hL3) and infective third-stage larvae (iL3) of the S. ratti Tokyo strain. hL3 were collected from rat heads at 30 h post-infection. Differential expression analysis revealed 664 upregulated genes in hL3. Functional annotation showed enrichment of genes encoding astacin metalloproteases and sperm-coating protein/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) protein families—both associated with tissue invasion and immune modulation. Quantitative RT-PCR was used to validate selected differentially expressed genes. Seven hL3-specific astacin genes were identified, of which six belonged to the M12A group. One hL3-specific astacin gene showed domain similarity to strongylastacin, a known tissue-penetration protein. Two SCP/TAPS genes were unique to hL3 and were absent from parasitic females, suggesting distinct roles in larval migration. By contrast, G protein-coupled receptor genes, particularly those related to chemosensory functions, were not upregulated in hL3, indicating that these pathways may be less important during this stage. These results provide the first transcriptomic profile of hL3 in S. ratti, and identify potential molecular mechanisms driving larval migration and immune evasion during host infection.