Abstract
BackgroundScorpions like other venomous animals posses a highly specialized organ that produces, secretes and disposes the venom components. In these animals, the last postabdominal segment, named telson, contains a pair of venomous glands connected to the stinger. The isolation of numerous scorpion toxins, along with cDNA-based gene cloning and, more recently, proteomic analyses have provided us with a large collection of venom components sequences. However, all of them are secreted, or at least are predicted to be secretable gene products. Therefore very little is known about the cellular processes that normally take place inside the glands for production of the venom mixture. To gain insights into the scorpion venom gland biology, we have decided to perform a transcriptomic analysis by constructing a cDNA library and conducting a random sequencing screening of the transcripts.ResultsFrom the cDNA library prepared from a single venom gland of the scorpion Hadrurus gertschi, 160 expressed sequence tags (ESTs) were analyzed. These transcripts were further clustered into 68 unique sequences (20 contigs and 48 singlets), with an average length of 919 bp. Half of the ESTs can be confidentially assigned as homologues of annotated gene products. Annotation of these ESTs, with the aid of Gene Ontology terms and homology to eukaryotic orthologous groups, reveals some cellular processes important for venom gland function; including high protein synthesis, tuned posttranslational processing and trafficking. Nonetheless, the main group of the identified gene products includes ESTs similar to known scorpion toxins or other previously characterized scorpion venom components, which account for nearly 60% of the identified proteins.ConclusionTo the best of our knowledge this report contains the first transcriptome analysis of genes transcribed by the venomous gland of a scorpion. The data were obtained for the species Hadrurus gertschi, belonging to the family Caraboctonidae. One hundred and sixty ESTs were analyzed, showing enrichment in genes that encode for products similar to known venom components, but also provides the first sketch of cellular components, molecular functions, biological processes and some unique sequences of the scorpion venom gland.
Highlights
Scorpions like other venomous animals posses a highly specialized organ that produces, secretes and disposes the venom components
Results cDNA library and expressed sequence tags (ESTs) analysis The H. gertschi venom gland library constructed was not amplified (2.8 × 105 cfu/mL with 99% recombinant clones); the cluster size might reflect the relative abundance of the corresponding mRNA population
160 electropherograms were submitted to bioinformatics analysis to remove vector and poor quality sequences, resulting in 147 high-quality ESTs which were used to analyze gene expression profile in the H. gertschi venom glands
Summary
Scorpions like other venomous animals posses a highly specialized organ that produces, secretes and disposes the venom components. The most prominent components of scorpion venoms are the peptides responsible for the neurotoxic effects associated with their sting, for which more than 350 different have been described (extensive databases can be found in Tox-Prot [1] and SCORPION [2]) Most of these toxins are structurally related disulphide-rich short proteins (23–75 amino acid residues long), which affect cellular communication by modulating Na+ or K+ ion-channels permeability [3]. Due to their importance in scorpion envenomation and their usefulness as molecular and pharmacological probes for studying ion-channels, most of the work performed to date are focused at these neurotoxins, with relative few other components ever described; among which are heterodimeric phospholipases A2 These numbers contrast heavily with the known universe of protein components (near four hundreds) described to exist in scorpion venoms, from which only about 12% are not classified within the known scorpion toxin families
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