A Survey of Snake Toxin Genes through a Comparative Transcriptomic Analysis of the Body Organs from B. jararaca

The snake venom gland (VG) is a very specialized organ capable of producing high amounts of proteins that are stocked in the lumen at high concentrations. Despite the large knowledge acquired on certain venoms, there are no systematic high throughput studies aiming at characterizing the toxin related genes expressed in other body tissues. In this study, we sequenced, using 454-Roche technology, mRNAs from different organs (VG, pancreas, brain, lung, heart, liver and kidney) from Bothrops jararaca, Viperidae, to gather some information about those genes related to venom products. This allowed the assembly of a high coverage transcript panorama of the species, represented by about 35.000 unique combined sequences resulting from around 1.2 million long reads. These unigenes were further annotated by similarity and Gene Ontology and the reads mapped back to identify genes and pathways that are VG-specific or differentially expressed. For instance, chaperones and proteins involved in disulfide bonds are extremely highly expressed in the VG. We also compared VG in the 4^th day of venom producing circle from animals treated or not with agonists and antagonists of adrenoreceptors that seem to regulate the venom system. Moreover, sequences related to toxin gene families, such as cobra venom factor, VEGF, cystatin, C-type lectin, among other, were found in other tissues providing invaluable elements for phylogenetic analysis of protein families. This reference transcriptome is also being used to guide a de novo assembly of B. jararaca genome focusing on the identification of key elements in the venom related genes.