Analysis Of Scorpion Toxin Diversity And Its Genetic Basis

Scorpions have successfully survived for over400million years on earth, and widely spread all over the world, which is mainly owing to their powerful venom systems. Scorpions use their venoms srecreted by glands to prey and defense. Proteins and peptides, called "scorpion toxin", are the major bioactive components in venoms, and have been widely studied as a rich source for drug design and development. Scorpion venom components are highly diversified among different genera, species, individuals, especially different families. However, most researches were focused on a few scorpion species from the family buthidae so far. Actually, there are a large number of new toxins in the vast non-buthidae scorpion species, which are worthy of mining and developing. By the venom gland transcriptome analyses of the chaerilidae scorpions(Chaerilus tryznai and Chaerilus tricostatus) and the euscorpiidae scorpion (Euscorpiops validus), we discovered large number of new toxin molecules from their venoms. Based on comparative transcriptome analysis, we found the molecular diversity of scorpion toxins between different families or genera,, Evolutionary analysis revealed the dynamic evolution of scorpion venom components from Buthidae to non-Buthidae. At the same time, there were no studies focused on the genetic basis of the molecular diversity of scorpion toxins on genomic level due to the absence of scorpion genomic data. This study utilized the whole genomic data of Mesobuthus martensii to identifiy all the toxin genes of M. martensii on the genome level, and analysed the organization and structure of its neurotoxin and defensin genes. The origin and evolution of M. martensii neurotoxin genes was deduced, and the genetic basis of the molecular diversity of M. martensii neurotoxins was also discussed.Firstly, we performed the venom gland transcriptome analyses of C. tryznai, C. tricostatus and E. validus, and identified a total of284novel toxins. Among them,159toxins belong to the known toxin types, including NaTx (toxins specific for sodium channels), a-KTx (a subfamily of toxins specific for potassium channels), β-KTx (β subfamily of toxins specific for potassium channels), calcine (toxins specific for ryanodine receptors), cytolytic peptides, bpp like peptides, scorpine like peptides, scamp (small cationtic antimicrobial peptides), glycine-rich peptides, lcamp (long cationic antimicrobial peptides), anionic peptides, Lal-like peptides, LVP (lipolysis activating peptides),8C-toxin, tibetanin, TIL (trypsin inhibitor like peptides), SPSV (serineprotease from scorpion venom), lysozyme, PLA2and salivary protein. In addition,125atypical toxin molecules were discovered, including two types specific to chaerilidae scorpions (called Chaertoxinl and Chaertoxin2) and one type specific to euscorpiidae scorpion (called Euscortoxinl). These results show the extreme diversity of scorpion toxins, and provide a rich source for drug design and development.Secondly, comparing the toxin types and abundance of Buthidae, Chaerilidae and other non-Buthidae families, we discovered four toxins (NaTx, P-KTx, scamp and bpp-like peptides) from the venoms of Chaerilidae, which were specific to Buthidae scorpions previously, while the abundance of AMPs in Chaerilidae was more similar to that in non-Buthidae families. The results indicate that Chaerilidae scorpions not only contain the toxin types that were previously observed exclusively in buthids but also contain highly expressed toxin types previously characterized in non-buthids. Chaerilidae scorpions appear to have a specific venom arsenal that is intermediate between Buthidae and non-Buthidae families. Based on phylogenetic analysis, we speculated that both NaTx,(3-KTx and bpp-like genes were recruited into venom before the lineage split between Buthidae and non-Buthidae. By comparative transcriptome analyses of the euscorpiidae scorpion E. validus and S. jendeki, we discovered that although the toxin types of the two scorpions had no difference, the toxin abundance of the two scorpions was different each other, which displayed the molecular diversity of the venom components within the family Euscorpiidae. All these data enriched and enhanced our knowledge on the diversity of scorpion toxins.Finally, we utilized the whole genomic data of M. martensii to analyze the diversity of scorpion toxin genes on the genome level and its genetic basis. A total of198toxin genes were characterized from the genome of M. martensii, including116neurotoxin genes (61NaTx,46KTx,5C1Tx and4CaTx),14LVP genes,8AMPs genes,19PLA2genes,2hyaluronidase genes,15metalloprotease genes and24other toxin-like peptides genes. Analyzing the organization and structure of116neurotoxin genes, we found the majority of neurotoxin genes had a common gene structure, constituted by a phase-I intron and two exons. Moreover, half of neurotoxin genes were found to exist in cluster on the M. martensii genome, which revealed that a larger number of neurotoxin genes had duplicated in genome. By comparing the organizational structures of neurotoxin and defensin genes, we discovered that neurotoxin and defensin shared similar gene organization and structure, which confirmed that they had a common origin. Based on phylogenetic analysis, we deduced the origin and evolution of neurotoxin genes:NaTx genes firstly diverged from the ancestral gene, and then C1Tx genes, KTx genes and defensin genes were differentiated.Overall, our work performed a comprehensive investigation on the toxin diversities of C. tryznai, C. tricostatus and E. validus at the transcriptome level. A total of284novel toxins have been characterized, which could provide numerous candidate molecules for drug design and development. Comparative transcriptome analysis revealed the diversity of scorpion toxins between different families or genera. Evolutionary analysis clued the dynamic evolution of scorpion venom components from Buthidae to non-Buthidae.198toxin genes were characterized from the genome of M. martensii. Then the analyses of organizational structure, origin and evolution of the neurotoxin genes shed insights into the genetic basis of the diversity of scorpion toxins.