title: A combined proteomic and transcriptomic analysis of slime secreted by the southern bottletail squid, Sepiadarium austrinum (Cephalopoda).
abstract: Sepiadarium austrinum, the southern bottletail squid, is a small squid that inhabits soft sediments along Australia's south-east coast. When provoked, it rapidly secretes large volumes of slime, presumably as a form of chemical defense. We analyzed the proteomic composition of this slime using tandem mass spectrometry and transcriptomics and found that it was remarkably complex with 1735 identified protein groups (FDR:0.01). To investigate the chemical defense hypothesis we performed an Artemia toxicity assay and used sequence analysis to search for toxin-like molecules. Although the slime did not appear to be toxic to Artemia we found 13 proteins in slime with the hallmarks of toxins, namely cysteine richness, short length, a signal peptide and/or homology to known toxins. These included three short (80-130AA) cysteine rich secreted proteins with no homology to proteins on the NCBI or UniProt databases. Other protein families found included, CAP, phospholipase-B, ShKT-like peptides, peptidase S10, Kunitz BPTI and DNase II. Quantitative analysis using intensity based absolute quantification (iBAQ via MaxQuant) revealed 20 highly abundant proteins, accounting for 67% of iBAQ signal, and three of these were toxin-like. No mucin homologues were found suggesting that the structure of the slime gel may be formed by an unknown mechanism.
  
  
  
  This study is the first known instance of a slime secretion from a cephalopod to be analyzed by proteomics methods and is the first investigation of a member of the family Sepiadariidae using proteomic methods. 1735 proteins were identified with 13 of these fitting criteria established for the identification of putative toxins. The slime is dominated by 20 highly abundant proteins with secreted, cysteine rich proteins. The study highlights the importance of 'omics approaches in understanding novel organisms.
authors.affiliation: Department of Ecology, Environment and Evolution, School of Life Sciences, La Trobe University, Melbourne, Vic 3086, Australia. Electronic address: njcaruana@students.latrobe.edu.au.
authors.forename: Nikeisha J
authors.initials: NJ
authors.lastname: Caruana
authors.affiliation: Department of Molecular and Cell Biology, James Cook University, Townsville, Qld 4811, Australia; Department of Biochemistry and Genetics, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, Vic 3086, Australia.
authors.forename: Ira R
authors.initials: IR
authors.lastname: Cooke
authors.affiliation: Department of Biochemistry and Genetics, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, Vic 3086, Australia.
authors.forename: Pierre
authors.initials: P
authors.lastname: Faou
authors.affiliation: Sciences, Museum Victoria, Carlton, Vic 3053, Australia.
authors.forename: Julian
authors.initials: J
authors.lastname: Finn
authors.affiliation: Life Sciences Computation Centre, Victorian Life Sciences Computation Initiative, Carlton, Vic 3053, Australia.
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Hall
authors.affiliation: Sciences, Museum Victoria, Carlton, Vic 3053, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Norman
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, QLD 4072, Australia.
authors.forename: Sandy S
authors.initials: SS
authors.lastname: Pineda
authors.affiliation: Department of Ecology, Environment and Evolution, School of Life Sciences, La Trobe University, Melbourne, Vic 3086, Australia.
authors.forename: Jan M
authors.initials: JM
authors.lastname: Strugnell
mesh_terms: D000818:Animals; D049832:Decapodiformes / Q000737:chemistry* / Q000276:immunology; D005782:Gels / Q000737:chemistry; D020869:Gene Expression Profiling / Q000379:methods*; D011506:Proteins / Q000378:metabolism; D020543:Proteome / Q000032:analysis / Q000633:toxicity; D040901:Proteomics / Q000379:methods*
chemical_list: D005782:Gels; D011506:Proteins; D020543:Proteome
keywords: Cephalopod; Proteogenomics; Proteomics; Slime; Squid; Transcriptomics