Taxonomic Status And Immune Characteristics Of Mannose Receptor Of Sultan Fish(Leptobarbus Hoevenii)

Sultan fish（Leptobarbus hoevenii）,a freshwater fish species that has been introduced form Malaysia into China recently.It belongs to Cypriniformes Order,Cyprinidae Family,Barbinae Subfamily and Leptobarbus Genus.Since Sultan fish was introduced from foreign country,therefore it’s taxonomic status was analyzed basing on morphological features,skeleton structure and the sequences of mitochondrial cytochrome oxidase I（COI）.The results are as follows:The body shape was rhombus looked like grass carp（Ctenopharygodon idellus）.However Sultan fish had two pairs of whiskers.Color in life was silvery,fin tinged with red.The D,III-7;P,I-13-16;V,I-8;A,III-27-32;lateral line scales 34-36;transverse scales5_1/2/1/4_1/2;predorsal scales 13;gill rakers 5-6+9-11,totally 13-17.The Sultan fish skeleton system consists of axil skeleton and appendicular skeleton.Axil skeleton consists of skull,spine and rib.Appendicular skeleton consists of paired fins bone and odd fins bone.Furthermore,the detailed structures of skeleton were described.In addition,the phylogenetic tree of COI gene of Sultan fish and those from other members in Barbinae subfamily showed that Sultan fish was closely related to the members in Barbodes genus.With the expansion of the Sultan fish culture in China,the higher cultural density and deterioration of the water quality etc.have led to the outbreak of various diseases.Flavobacterium columnarium is a common pathogen which can infect Sultan fish and causes columnaris.The knowledge about the fish immune responses during the infection is critical for fish disease prevention.There have been reported that mannose receptor（MR）plays a critical role in innate and adaptive immunity of fish.In order to understand the structural characteristics of MR and its role in anti-infective immune responses in Sultan fish,we cloned and sequenced the MR of Sultan fish.Subsequently,real-time polymerase chain reaction（qRT-PCR）assay was used to measure the expression of the MR in the tissues of Sultan fish with or without F.columnare infection.The results showed that the MR of Sultan fish（LhMR）open reading frame was 4296 bp,encoding 1431 amino acids（aa）.The amino acid sequence and molecular structure of LhMR are highly similar to the MRs from other fish,i.e.,containing an extracellular ricin-likeβ-type clover domain（RICIN）,a fibronectin type II domain（FNII）and eight tandem C Lectin-like domains（CLECTs）,a transmembrane region and a short intracellular region.The mRNA of LhMR was widely expressed in 11 tested tissues,including spleen,kidney,heart,brain,skin,muscle,gills,liver,post intestine,fore intestine and mid intestine,with the highest expression level in the spleen.The mRNA expression of LhMR was significantly increased in the spleen,intestine,kidney and gills of Sultan fish infected with F.columnare measured by qRT-PCR.Furthermore,the protein expression of LhMR was also increased in the spleen,kidney and gill of Sultan fish infected with F.columnare revealed by immunochemistry assay.By Hematoxylin eosin staining,there were various pathological changes observed in the trunk kidney,intestine,liver and gills.In the trunk kidney,there were blood cells infiltrated in the renal tubules with necrosis in epithelial cells.The wall of intestine became thinner with diffused necrosis.Numerous vacuoles were observed in the liver cells.Gill lamella showed swollen,disordered,necrosis and detached.The results revealed that LhMR should play a role in the immune responses of Sultan fish infected with F.columnare.The current study will pave a new way for development prevention and therapy strategies against columnaris in Sultan fish.