title: The first mollusk spätzle homolog gene in the clam, Paphia undulate.
abstract: Spätzle, is the only identified endogenous Toll receptor ligand, plays a critical role in initiatinge innate immune responses and controlling dorsal-ventral axis formation in Drosophila. Here we identified the first spätzle gene homolog, Pu-Spz, in the marine mollusk Paphia undulate. The full-length of Pu-Spz cDNA is 1248 bp, including an open reading frame (ORF) of 702 bp, a 5'-untranslated region (UTR) of 26 bp and a 3'-UTR of 203 bp. The ORF encodes a 233-amino-acid protein with conserved domains; it includes a putative signal peptide and a C-terminal cystine-knot. Sequence alignment revealed that the cystine-knot domain of Pu-Spz contains six highly conserved Cys residues, which maintain a molecular conformation suitable for Toll receptor binding. Unlike Spätzle, Pu-Spz lacks a seventh Cys residue, which is essential for forming intermolecular disulfide bridge. Phylogenetic analysis revealed that Pu-Spz is closer to the homologs found in crustaceans than to those in the insect branch. Transcript abundance of Pu-Spz was increased after challenging P. undulate with either heat-killed Listeria monocytogenes or heat-killed Vibrio alginolyticus, suggesting Spätzle is involved in P. undulate host defense. Our results demonstrate convergent evolution of the spätzle-Toll system between the mollusk and arthropod lineages.
authors.affiliation: Engineering Research Center of Marine Biological Resource Comprehensive Utilization, Third Institute of Oceanography, State Oceanic Administration, Xiamen, 361005, China.
authors.forename: Mingjia
authors.initials: M
authors.lastname: Yu
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China.
authors.forename: Yuehuan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Engineering Research Center of Marine Biological Resource Comprehensive Utilization, Third Institute of Oceanography, State Oceanic Administration, Xiamen, 361005, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Tang
authors.affiliation: Department of Surgery, University of Wisconsin-Madison, Madison, WI, 53705, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China. Electronic address: yzhang@scsio.ac.cn.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D049872:Bivalvia / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D007113:Immunity, Innate; D008024:Ligands; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D051193:Toll-Like Receptors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D008024:Ligands; D012333:RNA, Messenger; D051193:Toll-Like Receptors
keywords: Innate immune; Ligand; Paphia undulate; Spätzle; Toll-like receptor