Combined Proteomic and Transcriptomic Interrogation of the Venom Gland of Conus geographus Uncovers Novel Components and Functional Compartmentalization*

Cone snails are highly successful marine predators that use complex venoms to capture prey. At any given time, hundreds of toxins (conotoxins) are synthesized in the secretory epithelial cells of the venom gland, a long and convoluted organ that can measure 4 times the length of the snail's body. In recent years a number of studies have begun to unveil the transcriptomic, proteomic and peptidomic complexity of the venom and venom glands of a number of cone snail species. By using a combination of DIGE, bottom-up proteomics and next-generation transcriptome sequencing the present study identifies proteins involved in envenomation and conotoxin maturation, significantly extending the repertoire of known (poly)peptides expressed in the venom gland of these remarkable animals. We interrogate the molecular and proteomic composition of different sections of the venom glands of 3 specimens of the fish hunter Conus geographus and demonstrate regional variations in gene expression and protein abundance. DIGE analysis identified 1204 gel spots of which 157 showed significant regional differences in abundance as determined by biological variation analysis. Proteomic interrogation identified 342 unique proteins including those that exhibited greatest fold change. The majority of these proteins also exhibited significant changes in their mRNA expression levels validating the reliability of the experimental approach. Transcriptome sequencing further revealed a yet unknown genetic diversity of several venom gland components. Interestingly, abundant proteins that potentially form part of the injected venom mixture, such as echotoxins, phospholipase A(2) and con-ikots-ikots, classified into distinct expression clusters with expression peaking in different parts of the gland. Our findings significantly enhance the known repertoire of venom gland polypeptides and provide molecular and biochemical evidence for the compartmentalization of this organ into distinct functional entities.