Characterization of the full-length transcriptome of female Eucoleus annulatus and comparative transcriptomic analysis of its head, middle, and tail body sections

BACKGROUND: Eucoleus annulatus is a parasitic nematode that inhabits the upper digestive tract of avian hosts, posing significant threats to avian health and poultry production. However, the gene information and gene expression characteristics underlying its physiological specialization and parasitic adaptation remain poorly understood. METHODS: In this study, we applied an integrated transcriptomic approach to generate a high-quality full-length transcriptome of E. annulatus using PacBio Iso-Seq and to characterize body section-specific gene expression patterns using Illumina RNA sequencing (RNA-Seq). Differentially expressed transcripts (DETs) among its head, middle, and tail sections were identified, and their functional annotations were assessed through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. RESULTS: PacBio Iso-Seq generated 21,951 high-confidence, non-redundant full-length transcript isoforms, among which 6921 were annotated in the Nr, Pfam, COG, KEGG, and GO databases. Comparative RNA-Seq analysis revealed pronounced section-specific transcriptional divergence, with 1570, 1533, and 1600 DETs enriched in the head, middle, and tail sections, respectively. DETs in the head were significantly enriched in pathways related to amino acid metabolism, RNA processing, and ion transport, while the DETs in the middle body section were primarily associated with glycolysis, oxidative phosphorylation, and transcriptional regulation, indicating elevated metabolic and transcriptional activity. DETs in the tail were significantly enriched in processes related to protein degradation, structural maintenance, and stress adaptation, suggesting roles in environmental response and physiological resilience. CONCLUSIONS: This study, for the first time, reports the first full-length transcriptome of E. annulatus and reveals distinct gene expression profiles across different body sections. These findings provide valuable molecular insights into the spatial organization of gene expression in E. annulatus and establish a foundation for studying its biology and host-parasite interactions in the future.