Combined Transcriptomic and Proteomic Analysis of the Posterior Salivary Gland from the Southern Blue-Ringed Octopus and the Southern Sand Octopus

Abstract

This study provides comprehensive proteomic profiles from the venom producing posterior salivary glands of octopus (superorder Octopodiformes) species. A combined transcriptomic and proteomic approach was used to identify 1703 proteins from the posterior salivary gland of the southern blue-ringed octopus, Hapalochlaena maculosa and 1300 proteins from the posterior salivary gland of the southern sand octopus, Octopus kaurna. The two proteomes were broadly similar; clustering of proteins into orthogroups revealed 937 that were shared between species. Serine proteases were particularly diverse and abundant in both species. Other abundant proteins included a large number of secreted proteins, many of which had no known conserved domains, or homology to proteins with known function. On the basis of homology to known venom proteins, 23 putative toxins were identified in H. maculosa and 24 in O. kaurna. These toxins span nine protein families: CAP (cysteine rich secretory proteins, antigen 5, parthenogenesis related), chitinase, carboxylesterase, DNase, hyaluronidase, metalloprotease, phospholipase, serine protease and tachykinin. Serine proteases were responsible for 70.9% and 86.3% of putative toxin expression in H. maculosa and O. kaurna, respectively, as determined using intensity based absolute quantification (iBAQ) measurements. Phylogenetic analysis of the putative toxin serine proteases revealed a similar suite of diverse proteins present in both species. Posterior salivary gland composition of H. maculosa and O. kaurna differ in several key aspects. While O. kaurna expressed the proteinaceous neurotoxin, tachykinin, this was absent from H. maculosa, perhaps reflecting the acquisition of a potent nonproteinaceous neurotoxin, tetrodotoxin (TTX) produced by bacteria in the salivary glands of that species. The dispersal factor, hyaluronidase was particularly abundant in H. maculosa. Chitinase was abundant in both species and is believed to facilitate envenomation in chitinous prey such as crustaceans. Cephalopods represent a largely unexplored source of novel proteins distinct from all other venomous taxa and are of interest for further inquiry, as novel proteinaceous toxins derived from venoms may contribute to pharmaceutical design.

Venomics of Remipede Crustaceans Reveals Novel Peptide Diversity and Illuminates the Venom’s Biological Role

“…Octopus venom proteases specifically target muscle attachment sites in crabs, which allows the octopus to easily extract their muscle tissue [ 43 , 44 , 45 ]. In accordance with this venom role serine protease transcripts are the most highly expressed venom protein transcripts in both octopus and cuttlefish posterior salivary glands [ 35 , 36 , 46 , 47 ]. A similarly high level of PS1 expression in remipede venom glands is compatible with the idea that they too use their venom to detach the soft tissue of their prey from the exoskeleton, helping with prey ingestion and pre-digestion.…”

“…Likewise, PS1 enzymes are represented by the highest transcript diversity of all venom proteins, a result that corresponds closely to our initial study [ 12 ]. Serine peptidases are present in a broad range of venoms, but the extraordinarily high level of expression in remipede venom glands most closely parallels the expression found in the venom glands of some predators such as vipers, helodermatid lizards, and cephalopods [ 35 , 36 , 37 , 38 , 39 ]. PS1s could play a variety of roles in remipede venom.…”

Comparative analyses of glycerotoxin expression unveil a novel structural organization of the bloodworm venom system

“…The cephalopod venom apparatus comprises two pairs of histologically different venom glands, named posterior and anterior venom glands [58]. Whereas analyses on the posterior venom glands in cephalopods revealed toxins that convergently evolved in other venomous animals [59–61], the role of the anterior glands remains poorly investigated. These glands are considered as mucus secreting organs [58] but their contribution to the cephalopod venom cocktail remains unclear, even though it was recently shown that they may also express some toxin transcripts [62].…”

Coupled Genomic Evolutionary Histories as Signatures of Organismal Innovations in Cephalopods

“…Additionally, there are few transcriptomes of cephalopod venom glands that can provide information on expression within the tissue . Despite this, a dynamic evolutionary picture is emerging, for example, a loss of tachykinin expression in the venom gland has been observed in the southern blue‐ringed octopus ( Hapalochlaena maculosa ) . Due to the inclusion of the potent non‐proteinaceous neurotoxin tetrodotoxin (TTX) in H. maculosa , proteinaceous neurotoxins are considered to be redundant.…”