Alternative mRNA Splicing in Three Venom Families Underlying a Possible Production of Divergent Venom Proteins of the Habu Snake, Protobothrops flavoviridis

Abstract

Snake venoms are complex mixtures of toxic proteins encoded by various gene families that function synergistically to incapacitate prey. A huge repertoire of snake venom genes and proteins have been reported, and alternative splicing is suggested to be involved in the production of divergent gene transcripts. However, a genome-wide survey of the transcript repertoire and the extent of alternative splicing still remains to be determined. In this study, the comprehensive analysis of transcriptomes in the venom gland was achieved by using PacBio sequencing. Extensive alternative splicing was observed in three venom protein gene families, metalloproteinase (MP), serine protease (SP), and vascular endothelial growth factors (VEGF). Eleven MP and SP genes and a VEGF gene are expressed as a total of 81, 61, and 8 transcript variants, respectively. In the MP gene family, individual genes are transcribed into different classes of MPs by alternative splicing. We also observed trans-splicing among the clustered SP genes. No other venom genes as well as non-venom counterpart genes exhibited alternative splicing. Our results thus indicate a potential contribution of mRNA alternative and trans-splicing in the production of highly variable transcripts of venom genes in the habu snake.

The origin and diversification of a novel protein family in venomous snakes

“…Similarly, amplification of a minor activity or escape from adaptive conflict between the cysteine-rich, disintegrin, or metalloproteinase domains could explain the evolution of P-II and P-I genes. It has recently been reported that alternative splicing of the SVMP genes in the habu snake (an Asian viper) can generate transcripts which encode different combinations of domains (48). Gene deletions that reduce the proteins from three to two domains (mdc to mad) or two to one domain (mad to mpo) would relieve potential conflict among isoforms and allow for optimization of minor activities.…”

Causes and Consequences of Snake Venom Variation

“…Recent studies have also highlighted the role of alternative-and trans-splicing in generating snake venom diversity (Figure 1). Genome-wide surveys of the transcriptional repertoire have led to the identification of alternative splicing in genes that encode SVMPs, snake venom serine proteases (SVSP) and vascular endothelial growth factors (VEGF), and trans-splicing in SVSP genes [42,46]. Rapid evolution under positive selection has been widely documented to facilitate adaptations in the natural world.…”

Optimization of the de novo assembly of the transcriptome of the venom gland of Pamphobeteus verdolaga, prospecting novel bioactive peptides

“…All the smaller P. verdolagas' ORFs are hypothesized to be then smaller isoforms of the best score homolog proteins, as the Augustus prediction algorithm identi ed them as complete transcripts and the global identity was above 20% (51). The varying lengths of these ORFs, which represent 7 to 27% of the best score homolog proteins primary structure, could be indicators of splicing events within the venom gland of spiders, as it has been described before in other venomous species (53,54), and therefore could also imply similar biological function. On the other hand, ORFs with the smallest global identity show between 58 and 164% of the best homolog protein's length, implying enough variability within the primary structure as to assume probable different biological activities to those of their homologs (51).…”