SCARS OF THE MOLECULAR EVOLUTION OF SNAKE TOXINS REVEALED BY TRANSCRIPTOMIC STUDIES

JUNQUEIRA-DE-AZEVEDO I. L. M. (1,2,3); CHING, A. T. C. (1,2); LEÃO, L. I. (1,3); HO, P. L. (1,2,3)

(1) Centro de Biotecnologia, Instituto Butantan, São Paulo, SP, Brazil. (2) Interunidades em Biotecnologia and (3) Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.

Snake toxins are largely known to undergo various evolutionary processes, such as gene duplication, intense paralogy, accelerated evolution, multiple recruitments of important scaffolds, simplification of multidomain structures and others. In the last years, a huge amount of transcriptomic data from snake venom glands, mainly provided by ESTs (Expressed Sequence Tags) initiatives, were made available. Besides profiling the toxin expression in such tissues and describing new toxins unlikely to be found by venom based analysis, these approaches also reveal unusual toxin variants and cellular transcripts, opening windows for the investigation of toxin and venom gland evolution and physiology. Analyzing the whole amount of data, publicly available and those from our databases generated from Viperidae, Elapidae and Colubridae species, we found some interesting features of toxin and non-toxin cDNAs that are discussed here. For instance, the metalloprotease sequences reveal scars of several kinds of evolutionary process, from gene duplication by a retrotransposon-like insert to the loss of domains by stop codon mutations and segment exchanges. In accordance, retrotransposon sequences are found in the untranslated regions of some toxin genes, and curiously, somatically transcribed at high levels in the venom glands. Old scaffolds of some very known toxins, such as the carbohydrate binding domains (CRD) of C-type lectins, appear to be recruited more than once in the venom evolution, and others, like the three-finger domain (3FTx) of alpha-neurotoxins, may be widespread in unlikely venoms, such as from a Viperidae. These and other observations reinforce the idea of a rapid evolution of the venom system and provide the evidences of the involved mechanisms.

KEY WORDS: transcriptome, venom, molecular evolution, retrotransposon.

FINANCIAL SUPPORT: FAPESP, Fundação Butantan

CORRESPONDENCE TO: Av. Vital Brasil, 1500, Instituto Butantan, 05503-900, São Paulo-SP, Brazil, Centro de Biotecnologia +55 11 37267222 ext 2244 email: ijuncaze@butantan.gov.br