RNA-Seq and Rattlesnakes

Animal toxins represent a valuable source of pharmacologically active macromolecules, a unique system for studying molecular adaptation, and a powerful framework for examining structure-function relationships in proteins. Snake venoms in particular represent a tremendous opportunity to study a large, integrated system of proteins that contribute to a single, well-defined, ecologically critical phenotypic trait. As these proteins and peptides are produced in dedicated glands, transcriptome sequencing has proven to be an effective approach to identifying the expressed toxin genes.

Researchers at Florida State University set out to study molecular evolutionary patterns in all of the genes that contribute to a single, defined, evolutionarily critical phenotype, the ability to produce venom. So they generated a venom-gland transcriptome for the Eastern Diamondback Rattlesnake (Crotalus adamanteus) using Roche 454 sequencing technology.

They identified 40 unique toxin transcripts, 30 of which have full-length coding sequences, and 10 have only partial coding sequences. They found toxins from 11 previously described families of snake-venom toxins and have discovered two putative, previously undescribed toxin classes. The most diverse and highly expressed toxin classes are the serine proteinases, metalloproteinases, and C-type lectins. The serine proteinases are the most abundant class, accounting for 35% of the toxin sequencing reads.

Rokyta DR, Wray KP, Lemmon AR, Lemmon EM, Caudle SB. (2011) A high-throughput venom-gland transcriptome for the Eastern Diamondback Rattlesnake (Crotalus adamanteus) and evidence for pervasive positive selection across toxin classes. Toxicon [Epub ahead of print]. [abstract]