Transcriptomic analysis reveals that pyruvate kinase potentially plays a key role in the differentiation of Spirometra mansoni proglottids by regulating the glycolysis pathway

Background The differentiation and maturation of proglottids constitute the basis for the growth and development of tapeworms. However, little is known about the molecular mechanisms underlying the differentiation of the proglottids of Spirometra mansoni. Methodology/Principal findings Here, the nanopore sequencing method was used to perform full-length transcriptomic analysis of 3 types of proglottids (scolex-neck-immature proglottids, SNIPs; mature proglottids, MPs; and gravid proglottids, GPs) of S. mansoni. Comparative transcriptomic analysis revealed that pyruvate kinase (PK) is a key gene affecting segmental differentiation. The PK family members of S. mansoni (SmPKs) were subsequently screened and systematically analysed. Moreover, a representative member, SmPK1, was chosen for cloning, expression and functional characterization. A total of 4,486 differentially expressed genes (DEGs) were identified across the 3 proglottid types. GO analysis revealed that the DEGs were enriched mostly in metabolism-related terms. KEGG enrichment analysis and GSEA further revealed that the degree of enrichment of the glycolysis pathway gradually increased as the segments developed and matured. Protein‒protein interaction (PPI) analysis confirmed that PK occupies a central position among energy metabolism-related genes and plays key roles in glycolysis. On the basis of the omics data, 4 SmPKs were identified. Phylogenetic analysis revealed that SmPKs have undergone varying degrees of evolution and exhibit high diversity. The optimal reaction conditions for recombinant SmPK1 (rSmPK1) were 37 °C and pH 8.0, and the addition of K ⁺ /Mg² ⁺ significantly enhanced its catalytic activity. Tannic acid significantly inhibited the activity of SmPK1 in vitro, reduced the production of pyruvate, and forced the organism to compensate for the energy supply through rapid lipolysis and delayed glycogen depletion, thereby affecting energy metabolism in tapeworms. Conclusions This study provides the first comprehensive characterization of gene expression profiles across different proglottids of S. mansoni. PK plays a pivotal role in proglottid differentiation, and this finding lays the foundation for further exploration of the differentiation mechanism of segments in tapeworms.