Genome Sequencing, Comparative Genomics And Insulin Signaling Pathway Analyses Of Taenia Saginata And Taenia Asiatica

Taenia saginata and Taenia asiatica are zoonotic parasites of great medical and economic importance. They shared very similar external features, leading to controversy about their evolutionary relationship in history. Due to the lack of fundamental researches on these paprasites, limited knowledge is known about mechanisms of their evolution, regulation on growth and development, adaption to paratism, host-parasite interaction, and immune evasion; studies on disease control and treatments for them are partly stcuked. Therefore, in this study we sequenced the genomes and transcriptomes of the two parasites and achieved assembliies and annatitions of their draft genomes; some genomic features between them were comprehensively compared and potential drug targets coupled with secreted proteins were also identified from a genome-wide scale; emphases were also placed on the phylogenomic analysis and its optimized strategies for the sequenced cestodes, as well as positive selection analysis on the two parasites. Moreover, putative genes encoding insulin-like peptides(ILP) and other components of the signaling pathway were identified and analysed in the tapeworms for the first time. The results in this study:1. The genomes of T.saganita and T. asiatica were sequenced at about 95-fold coverage, and assembled into about 170 Megabase(Mb) draft genomes, of which the scaffolds N50 are 568 kilobases(kb) and 342 kb respectively.2. Repeat sequences, protein coding genes and non-coding genes were identified from both the two genomes and annoated for their functions, Gene Ontology(GO) and KEGG pathways; a bimodal intron length distribution and GC usage basis for short introns were found for the gene structures of both the two tapeworms.3. The transcriptomes of pre- and post- bile-activated T. saginata larvae stages and T. asiatica adult stage were sequenced and assmblied into gene transcripts with alternative splicing and expression information.4. Comparative genomic analyses revealed that T. saginata and T. asiatica shared features of high genome synteny, low sequence divergence and similar gene family evolution, implying greatly close evolutionary releationship between them;some gene families were found to evolute accordingly with their adaptation to parasitism.5. Potential drug target sequences including G protein-coupled receptors, proteases, kinases and ion channels were identified from the two tapeworms’ genomes and compared with the known sequences from drug target databases; secreted proteins were also identified and discussed for their possible functions.6. Phylogenomic analysis confirmed the phylogenetic releationships of T. saginata, T. asiatica and T.solium, as well as other platyhelminths; a new strategy based on calculation of correlation between the genetic distances was proposed to reduce the random errors from the phylogenetic marker selection, in order to improve phylogenetic analysis result for Taenia tapeworms; this strategy can also be applied in molecular epidemiology analyses, like genotyping for some viruses.7. Positive selection analysis along each lineage revealed a strong signal of adaptation associated with host changes; in T. asiatica genome, the genes related to its host shift and tissue tropism were also included in the positively selected genes.8. ILP genes were identified from the tapeworms’ genomes for the first time, which confuted the hypothesis that taprworms probably employ host-derived insulin signal to regulate their growth and development due to the lack of endogenous ILPs; the ILPs of parasitic platyhelminths were typical with insulin family features and conserved gene structure; the m RNA expression and immunochemistry analyses showed that tapeworms’ ILPs were predominantly located in the ovarian tissue of mature proglottid, implying functions related to reproduction.