Transcriptome analysis of the venom gland of the Mexican scorpion Hadrurus gertschi (Arachnida: Scorpiones)

BMC Genomics BioMed Central Open Access Research article Transcriptome analysis of the venom gland of the Mexican scorpion Hadrurus gertschi (Arachnida: Scorpiones) Elisabeth F Schwartz1,2, Elia Diego-Garcia1, Ricardo C Rodríguez de la Vega1 and Lourival D Possani*1 Address: 1Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001 Cuernavaca 62210, Mexico and 2Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF, 70910-900, Brasil Email: Elisabeth F Schwartz - ; Elia Diego-Garcia - ; Ricardo C Rodríguez de la Vega - ; Lourival D Possani* - * Corresponding author Published: 16 May 2007 BMC Genomics 2007, 8:119 doi:10.1186/1471-2164-8-119 Received: 17 March 2007 Accepted: 16 May 2007 This article is available from: http://www.biomedcentral.com/1471-2164/8/119 © 2007 Schwartz et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Scorpions 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. Results: From 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. Conclusion: To 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. Page 1 of 12 (page number not for citation purposes) BMC Genomics 2007, 8:119 Background Scorpion venoms are very complex mixtures with hundreds of different components produced by the highly specialized venom glands. 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 (v.gr. [4-6]), non-disulphide short peptides with cytolytic activity and a few other functions [7,8]. Recent proteomic analyses [9-16] have documented the overall composition for nine scorpion species, all of them from the family Buthidae and most of them belonging to the Tityus genus. These analyses confirmed the gross estimation of an average of one hundred different proteins in each one of the venoms [17]. Approximately half of them comprehend components with molecular masses in the range of commonly found scorpion toxins (2,000–8,000 Da). 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. Further insights into scorpion venom compositions have been achieved by gene cloning by PCR-based methods conducted with cDNA libraries. For example, almost one hundred toxin precursors have been sequenced from venom gland libraries of the buthid scorpion Mesobuthus martensii (v.gr. [18-20]). Unfortunately the spectrum of sequences obtained through PCR-based approach is limited by the specificity of the PCR primers used. It is worth noticing that although PCR-based methods along with the abundant isolation and characterization of scorpion toxins and, more recently, proteomic profiling of whole venoms, have provided us with a large number of sequences, all these components are secreted from the venom glands. Little is known about the biological processes that are taking place inside the venom gland cells. Therefore, we elected to use a transcriptome approach to improve the understanding of the composition of Hadrurus gertschi venom gland. The scorpion H. gertschi Soleglad (1976) belongs to the family Caraboctonidae [21] and is considered no dangerous to humans. H. gertschi is endemic to Mexico, occurring exclusively in the State of Guerrero, and lives http://www.biomedcentral.com/1471-2164/8/119 underground in tunnels excavated in the soil. From the venom of this scorpion few components have been isolated and studied: hadrurin, an antimicrobial and cytolytic peptide [22]; HgeTx1, a K+ channel blocker [23]; hadrucalcine, a peptide capable of activating skeletal Ryanodine receptors [Schwartz et al., in preparation], and; the precursors HgeScplp and HgeβKTx, which encode for long-chain peptides similar to Scorpine and βKTx's, respectively [24]. Although hadrurin w (...truncated)