Origin and evolution of toxin gene families in Dipsadidae snakes

Abstract

Advanced snakes developed a specialized toxin-producing maxillary gland, enabling them to inoculate toxins into their preys. This gave them an advantage over other predators and allowed for their trophic niche diversification. Among the wide spectrum of snake diversity in the neotropics, the family Dipsadidae harbors the highest amount of species. Among them, we found venomous and non-venomous groups that possess astonishingly diverse ecologies. However, few are the works that have tackled the compositional and structural features of venom and toxins within this family, due to its low medical relevance. Interestingly, the few species that have been thoroughly analyzed have unveiled a wide array of enzymatic and non-enzymatic toxins, resembling venom of vipers and elapids, and even containing new toxin scaffolds, that are in some cases unique to Dipsadidae species. This is the case of svMMPs a recently described toxin family that was independently recruited in three separate tribes of the family. These proteolytic toxins evolved toward a simplified structure paralleling what is observed in SVMPs, the dominant proteolytic enzymes in most snake groups. Nevertheless, the processes and mechanisms that shaped the evolutionary trajectories of snake venom toxins have been greatly biased towards the medical relevant species of the Viperidae and Elapidae families, leaving behind the vast majority of snake diversity. Therefore, we intend to de novo assemble high quality genomes from three species from different tribes of the Dipsadidae family (Philodryadini, Tachymenini e Xenodontini) which have already been sequenced in the laboratory but not yet analyzed, and then annotate the toxin loci in order to understand their structural organization. With this information, we hope to provide a comprehensive view on how the genes of the main toxin families in snakes evolved within the Dipsadidae family and how it related to what is observed in venomous families of Elapidae and Viperidae, in a similar approach to what we previously did for B. jararaca genome (Almeida et al. PNAS 2021 Vol. 118 No. 20 e2015159118). We hope to determine which events allowed for the recruitment of the new/exclusive families we observe in this group, which is the case of svMMPs. (AU)