A naturally occurring non-coding fusion transcript derived from scorpion venom gland: implication for the regulation of scorpion toxin gene expression

Venom Systems as Models for Studying the Origin and Regulation of Evolutionary Novelties

A central goal in biology is to determine the ways in which evolution repeats itself. One of the most remarkable examples in nature of convergent evolutionary novelty is animal venom. Across diverse animal phyla, various specialized organs and anatomical structures have evolved from disparate developmental tissues to perform the same function, that is, produce and deliver a cocktail of potent molecules to subdue prey or predators. Venomous organisms therefore offer unique opportunities to investigate the evolutionary processes of convergence of key adaptive traits, and the molecular mechanisms underlying the emergence of novel genes, cells, and tissues. Indeed, some venomous species have already proven to be highly amenable as models for developmental studies, and recent work with venom gland organoids provides manipulatable systems for directly testing important evolutionary questions. Here, we provide a synthesis of the current knowledge that could serve as a starting point for the establishment of venom systems as new models for evolutionary and molecular biology. In particular, we highlight the potential of various venomous species for the study of cell differentiation and cell identity, and the regulatory dynamics of rapidly evolving, highly expressed, tissue-specific, gene paralogs. We hope that this review will encourage researchers to look beyond traditional study organisms and consider venom systems as useful tools to explore evolutionary novelties.

Overview of scorpion species from China and their toxins

Scorpions are one of the most ancient groups of terrestrial animals. They have maintained a steady morphology over more than 400 million years of evolution. Their venom arsenals for capturing prey and defending against predators may play a critical role in their ancient and conservative appearance. In the current review, we present the scorpion fauna of China: 53 species covering five families and 12 genera. We also systematically list toxins or genes from Chinese scorpion species, involving eight species covering four families. Furthermore, we review the diverse functions of typical toxins from Chinese scorpion species, involving Na⁺ channel modulators, K⁺ channel blockers, antimicrobial peptides and protease inhibitors. Using scorpion species and their toxins from China as an example, we build the bridge between scorpion species and their toxins, which helps us to understand the molecular and functional diversity of scorpion venom arsenal, the dynamic and functional evolution of scorpion toxins, and the potential relationships of scorpion species and their toxins.

Expression profiling of Drosophila mitochondrial genes via deep mRNA sequencing

Mitochondria play an essential role in several cellular processes. Nevertheless, very little is known about patterns of gene expression of genes encoded by the mitochondrial DNA (mtDNA). In this study, we used next-generation sequencing (NGS) for transcription profiling of genes encoded in the mitochondrial genome of Drosophila melanogaster and D. pseudoobscura. The analysis of males and females in both species indicated that the expression pattern was conserved between the two species, but differed significantly between both sexes. Interestingly, mRNA levels were not only different among genes encoded by separate transcription units, but also showed significant differences among genes located in the same transcription unit. Hence, mRNA abundance of genes encoded by mtDNA seems to be heavily modulated by post-transcriptional regulation. Finally, we also identified several transcripts with a noncanonical structure, suggesting that processing of mitochondrial transcripts may be more complex than previously assumed.

Characterization of a novel cDNA encoding a short venom peptide derived from venom gland of scorpion Buthus martensii Karsch: trans-splicing may play an important role in the diversification of scorpion venom peptides

A novel cDNA clone (named BmKT-u) which is a hybrid molecule of the 5'-terminal region of BmKT' cDNA and the 3'-terminal region of an undocumented cDNA (named BmKu), was isolated from a cDNA library made from the venom gland of scorpion Buthus martensii Karsch. BmKT-u codes for a 30 amino acid residue precursor peptide composed of a 20-residue signal sequence, and a putative 10-residue novel mature peptide. Northern blot hybridization showed BmKT-u cDNA is generated from a transcript. RT-PCR experiments excluded the possibility that BmKT-u cDNA is an artifact generated during reverse transcription. Genomic amplifications performed with three pairs of BmKT-u gene-specific primers showed the BmKT-u gene does not exist in the genome of the scorpion as a single transcriptional unit. Genomic cloning for BmKT' showed that the BmKT' gene contains an intron of 509 bp inserted into the region encoding the C-terminal region of the signal peptide. A sequence alignment comparison of the cDNA of BmKT-u with genomic BmKT' revealed that the junction site of the hybrid molecule is located at the 5'-splicing site of the intron. The data suggest that the BmKT-u transcript is a naturally occurring mature mRNA that is generated by trans-splicing. Trans-splicing may contribute to the diversity of venom peptides from venomous animals.

An overview of toxins and genes from the venom of the Asian scorpion Buthus martensi Karsch

Among the different scorpion species, Buthus martensi Karsch (BmK), a widely distributed scorpion species in Asia, has received a lot of attention. Indeed, over the past decade, more than 70 different peptides, toxins or homologues have been isolated and more peptides are probably still to be revealed. This review is focusing on the many peptides isolated from the venom of this scorpion, their targets, their genes and their structures. The aim is to give both a 'state of the art' view of the research on BmK venom and an illustration of the complexity of this scorpion venom. In the present manuscript, we have listed the different ion channel toxins and homologues isolated from the venom of BmK, either from the literature or from databases. We have described here 51 long-chain peptides related to the Na(+) channel toxins family: 34 related to the alpha-toxin family, four related to the excitatory insect toxin family, 10 related to the depressant insect toxin, one beta-like toxin plus two peptides, BmK AS and AS1, that act on ryanodine receptors. We also listed 18 peptides related to the K(+) channel toxin family: 14 short chain toxins or homologues, two long chain K(+) toxin homologues and two putative K(+) toxin precursors. Additionally, two chlorotoxin like peptides (Bm-12 and 12 b) have been isolated in the venom of BmK. Besides these ion channels toxins, two peptides without disulfide bridges (the bradykinin-potentiating peptide BmK bpp and BmK n1) and three peptides with no known functions have also been discovered in this venom. We have also taken the opportunity of this review to update the classification of scorpion K(+) toxins () which now presents 17 subfamilies instead of the 12 described earlier. The work on the venom of BmK led to the discovery of two new subfamilies, alpha-KT x 14 and alpha-KT x 17.