High-Throughput Identification and Analysis of Novel Conotoxins from Three Vermivorous Cone Snails by Transcriptome Sequencing

The venom of each Conus species consists of a diverse array of neurophysiologically active peptides, which are mostly unique to the examined species. In this study, we performed high-throughput transcriptome sequencing to extract and analyze putative conotoxin transcripts from the venom ducts of 3 vermivorous cone snails (C. caracteristicus, C. generalis, and C. quercinus), which are resident in offshore waters of the South China Sea. In total, 118, 61, and 48 putative conotoxins (across 22 superfamilies) were identified from the 3 Conus species, respectively; most of them are novel, and some possess new cysteine patterns. Interestingly, a series of 45 unassigned conotoxins presented with a new framework of C-C-C-C-C-C, and their mature regions were sufficiently distinct from any other known conotoxins, most likely representing a new superfamily. O- and M-superfamily conotoxins were the most abundant in transcript number and transcription level, suggesting their critical roles in the venom functions of these vermivorous cone snails. In addition, we identified numerous functional proteins with potential involvement in the biosynthesis, modification, and delivery process of conotoxins, which may shed light on the fundamental mechanisms for the generation of these important conotoxins within the venom duct of cone snails.

Conus Envenomation of Humans: In Fact and Fiction

Prominent hallmarks of the widely distributed, mainly tropical marine snail genus Conus are: (1) its unusually high species diversity; it is the largest genus of animals in the sea, with more than 800 recognized species; and (2) its specialized feeding behavior of overcoming prey by injection with potent neurotoxic, paralytic venoms, and swallowing the victim whole. Including the first report of a human fatality from a Conus sting nearly 350 years ago, at least 141 human envenomations have been recorded, of which 36 were fatal. Most Conus species are quite specialized predators that can be classified in one of three major feeding guilds: they prey exclusively or nearly so on worms, primarily polychaete annelids, other gastropods, sometimes including other Conus species, or fishes. These differences are shown to relate to the severity of human envenomations, with the danger increasing generally in the order listed above and a strong likelihood that all of the known human fatalities may be attributable solely to the single piscivorous species C. geographus.

Discovery Methodology of Novel Conotoxins from Conus Species

Cone snail venoms provide an ideal resource for neuropharmacological tools and drug candidates discovery, which have become a research hotspot in neuroscience and new drug development. More than 1,000,000 natural peptides are produced by cone snails, but less than 0.1% of the estimated conotoxins has been characterized to date. Hence, the discovery of novel conotoxins from the huge conotoxin resources with high-throughput and sensitive methods becomes a crucial key for the conotoxin-based drug development. In this review, we introduce the discovery methodology of new conotoxins from various Conus species. It focuses on obtaining full N- to C-terminal sequences, regardless of disulfide bond connectivity through crude venom purification, conotoxin precusor gene cloning, venom duct transcriptomics, venom proteomics and multi-omic methods. The protocols, advantages, disadvantages, and developments of different approaches during the last decade are summarized and the promising prospects are discussed as well.

Integrative taxonomy reveals that all the phenotype variations are not underpinned by genome in Conidae (Gastropoda, Mollusca)

The cone snails are hyper diverse group of marine gastropods and the shell morphology is the base of primary species identification. Among the Conidae, homoplasy and plasticity of morphological characters are common. Since speciation is positively correlated with peptide complexity in Conidae family, the present study was carried out to ascertain the genetic status of drastically varying phenotypes observed among the targeted Conus species of different environments and to detect cryptic species using mitochondrial and nuclear markers. Morphological parameters were recorded for the phenotypes of the species. Specific differences were observed for shell coloration. Three mitochondrial genes, COI (658bp), 16s rRNA (550bp), 12s rRNA (450bp) and Nuclear H3 gene (350bp) were amplified in five specimens each of varying phenotypes of targeted species. The analysis revealed that the phenotypic variations in C. inscriptus C.amadis and C.malacanus in different environments are not underpinned by the genome, The present study generated species-specific molecular signatures from varying phenotypes of conidae Since speciation is positively correlated with the complexity of conopeptides of the species, the findings provide confirmation of phenotypic variation and will be used for bioprospecting research on the species and also conservation and management of the species in Indian waters.

Integrative taxonomy reveals that all the phenotype variations are not underpinned by genome in Conidae (Gastropoda, Mollusca)

The cone snails are hyper diverse group of marine gastropods and the shell morphology is the base of primary species identification. Among the Conidae, homoplasy and plasticity of morphological characters are common. Since speciation is positively correlated with peptide complexity in Conidae family, the present study was carried out to ascertain the genetic status of drastically varying phenotypes observed among the targeted Conus species of different environments and to detect cryptic species using mitochondrial and nuclear markers. Morphological parameters were recorded for the phenotypes of the species. Specific differences were observed for shell coloration. Three mitochondrial genes, COI (658bp), 16s rRNA (550bp), 12s rRNA (450bp) and Nuclear H3 gene (350bp) were amplified in five specimens each of varying phenotypes of targeted species. The analysis revealed that the phenotypic variations in C. inscriptus C.amadis and C.malacanus in different environments are not underpinned by the genome, The present study generated species-specific molecular signatures from varying phenotypes of conidae Since speciation is positively correlated with the complexity of conopeptides of the species, the findings provide confirmation of phenotypic variation and will be used for bioprospecting research on the species and also conservation and management of the species in Indian waters.

Four new records of Conidae (Mollusca: Caenogastropoda) from the Andaman Islands, India

The Andaman and Nicobar archipelago comprises 572 islands spread over an area of 8,249 sq. km. These islands are within the 'Indo-Malayan region' and near the 'faunistic centre' from which other Indo-West Pacific regions recruit their tropical marine fauna (Ekman, 1953). The topographically complex nature of the nearshore environments of these islands creates a plethora of niches that support a rich and diverse molluscan fauna. Many of the Conus species (e.g., C. geographus Linnaeus, 1758; C. miles Linnaeus, 1758; and C. striatus Linnaeus, 1758) that occupy these islands are broadly distributed throughout the Indo-West Pacific. However, a few Indo-West Pacific species (e.g., Conus andamanensis Smith, 1878; and C. araneosus nicobaricus Hwass in Bruguière, 1792) are restricted to small geographic regions (Röckel et. al. 1995). Early oceanographic expeditions of the Andaman and Nicobar Islands that began in 1788 report only 10 Conus species from these islands (Smith, 1878; Melvill & Sykes, 1898; Preston, 1908). More recently, Subba Rao (1980) of the Zoological Survey of India (ZSI) reports a total of 51 Conus species from this region. In the past two decades, the Conus fauna has not been studied extensively due to lack of focused studies in the Andaman andNicobar Islands. Several recent surveys conducted by the Andaman and Nicobar Centre for Ocean Science and Technology investigated the intertidal and subtidal macrobenthic fauna of theAndaman Islands.