Cephalopods (squids, octopuses and cuttlefishes) comprise over 800 species, possess advanced nervous, cardiovascular and visual systems, and are masters of camouflage. Sepiadariidae, one family of benthic squids, possess specialized systems of secretion, secreting a viscous slime from their underside. It is believed that these secretions are involved in defending the species, and exhibit unique biochemical and biophysical properties including dramatic volume expansion, adhesion, and antimicrobial defence.
In order to further understand the mechanisms behind the secretion of the slime and the proteins strictly involved in it, six tissues from four individuals of the striped pyjama squid (Sepioloidea lineolata), underwent label free quantitation. The proteomic results were combined with a de novo transcriptome and analysed using computational bioinformatics methods, including a proteogenomic pipeline developed in Galaxy.
Seventy-eight proteins were highly differentially expressed within the slime and glands of S. lineolata, which included ten completely novel proteins. Gene Ontology term enrichment analysis also indicated a number of extracellular proteins involved in immune defence, catalytic peptidase activity, and protein binding. The identified proteins may have further implications for biomimetics such as the design of new pharmaceuticals and creation of non-toxic glues. A comparison of the proteins in the slime and glands found on the ventral epithelium of S. lineolata reveal that the slime does originate from these glands.
While traditionally quantitative proteomics is not used to analyse complete proteomes on non-model organisms, our work illustrates that the combination of de novo assembled transcriptomes and comprehensive bioinformatic analysis can provide rapid and informative investigation into species, which have high potential for biological applications without the need for a full genome. Our work incorporates the first label-free quantification analysis of a cephalopod and its secretion, and is also the first recording of the origin of the slime of Sepiadariidae from the secretion of specialised glands.