Differential Evolution of Complement Genes in Crocodilians

SALLY R ISBERG; SEBASTIÁN DUCHÊNE; ELIZABETH JONES; VICTORIA M LEE; PABLO SIROSKI; AMANDA CHONG1; CAROL LEE; CHRISTINE KEO; JAIME GONGORA; SIMON Y. W. HO; QAIS ALRAWAHI1; YI WEI; MARÍA SOLEDAD MOLEÓN

Santa Fe

Congreso; 25th Working Meeting of the Crocodile Specialist Group; 2018

The complement system plays an important role in the innate immune response in vertebrate and invertebrate taxa. It consists of about thirty proteins grouped in five major gene families. These encode for distinct plasma proteins that react with each other forming three activation cascades (alternative, lectin and classical) which converge in a single terminal pathway. Research of this system in crocodilians has focused on detecting serum activity but there is a knowledge gap about what genes are present and what evolutionary mechanism maintain the diversity in these taxa. To address this, we identified and investigated 20 complement system genes in the genomes of three crocodilian species (Alligator mississippiensis, Crocodylus porosus, and Gavialis gangeticus). We evaluated what gene evolved faster than the rest of complement genes. Individual and concatenated alignments were generated using ClustalW and Maximum likelihood method. Also, total tree length (TL) were calculated. For comparative purposes, we retrieve other immune loci from the three crocodilian genomes which include cytokines type I (INFA, INFE, INFK), Viperin and MHC class II genes. In addition, 15 exons representing 6 genes were selected and survey the diversity from additional 20 species of Alligatoridae and Crocodylidae. Phylogenetic analyses of the key complement components genes have shown a considerable level of sequence conservation among species. C1s and C3 had the highest TL, 0.26 and 0.13 respectively. Genetic distances between groups and within groups show that alligators have more variation than crocodiles. Finally, from orthologous clusters observed that crocodilian complement genes grouped within the five gene families, indicating that they have evolved independently from each other after speciation. Overall, our results suggest that crocodilians have the necessary gene repertoire for the potential activation of the three complement system pathways and there is some level of genetic diversity across species. This provides the foundations to conduct future studies on the diversity innate immune system of wild and captive populations to understand the immune response to diseases and inform management and conservation programs.