Identification Of A Myeloid Differentiation Factor 88 In Oncomelania Hupensis And Characterization Against Schistosoma Japonicum Infection

Background Myeloid differentiation factor 88(MyD88),an important link protein between Toll-like receptors(TLR)and protein kinase,could transfer signals to activate the transcription of nuclear factors and produce immunoactive substances from the upstream Toll-like receptors except TLR3.MyD88s have been proved to play an essential role in the innate immune response of some vertebrates and invertebrates,but not studied yet in Oncomelania hupensis(O.Hupensis).Objective To identify a myeloid differentiation factor 88-1(MyD88-1)in O.Hupensis,and characterize the role of MyD88-1 against Schistosoma japonicum(S.japonicum)infection.Methods The complete cDNA of MyD88-1 in O.hupensis was obtained using RACE-PCR,the structure of MyD88-1 was predicted and homologues sequences and conserved domains were aligned.A phylogenetic tree of MyD88s was further constructed with other species.In addition,the mRNA expression level of O.hupensis MyD88-1 before and after S.japonicum infection was investigated by Real-time PCR and In situ hybridization.Results The complete cDNA of O.hupensis MyD88-1 consists of 1406 bp open reading frame(ORF),encoding 468 amino acid residues which contains a death domain and a Toll/interlrukin-1 receptor(TIR)domain,the typical features of MyD88 family proteins.The predicted amino acid sequence of O.hupensis MyD88-1 shared 38%-52%identity with other mollusc.O.hupensis MyD88-1 was phylogenetically closest to Biomphalaria glabrata MyD88.Through Real-time PCR,the O.hupensis MyD88-1 existed in all inverstigated tissues and expressed highly in hemocytes,up-regulated in all tissues after S.japanicum infection except head-foot,with highest expression in hemocytes.The ISH assay revealed that there’s a weak MyD88-1 positive singal presenting in normal snail ’s glands and the positive signals became stronger at 6 h,12 h,96 h after S.japonicum infection,while not presented in head-foot’s muscles before and after S.japonicum infection.Conclusion MyD88-dependent signaling pathway is present in O.hupensis and plays an important role in hemocytes’s defense against S.japanicum infection.