TLR4 and TLR8 variability in Amazonian and West Indian manatee species from Brazil

Abstract

Amazonian (Trichechus inunguis) and West Indian (Trichechus manatus) manatees are aquatic mammals vulnerable to extinction found in the Amazon basin and the coastal western Atlantic. Toll-like receptors (TLR) play a key role in recognizing pathogen-associated molecular patterns using leucine-rich repeats (LRRs). We described the diversity of TLR4 and TLR8 genes in these two species of manatee. Amazonian manatee showed seven SNPs in TLR4 and the eight in TLR8, while West Indian manatee shared four and six of those SNPs, respectively. In our analysis, TLR4 showed one non-conservative amino acid replacement substitution in LRR7 and LRR8, on the other hand, TLR8 was less variable and showed only conserved amino acid substitutions. Selection analysis showed that only one TLR4 site was subjected to positive selection and none in TLR8. TLR4 in manatees did not show any evidence of convergent evolution compared to species of the cetacean lineage. Differences in TLR4 and TLR8 polymorphism may be related to distinct selection by pathogens, population reduction of West Indian manatees, or an expected consequence of population expansion in Amazonian manatees. Future studies combining pathogen association and TLR polymorphism may clarify possible roles of these genes and be used for conservation purposes of manatee species.

Figure 1 -. Map indicating the respective geographic collection sites of the manatees in North and Northeast regions of Brazil.

Figure 2 -. Identification of SNPs in the structure of the TLR4 gene. In the graph the higher frequency of nucleotides is represented in black with synonymous and non-synonymous occurrences in two populations of manatees. The cartoon structure is represented by exon 1 (red). Rectangles represent LRRs (1-19), LRR-CT, trans-membrane (TM) and intracellular (TM) domains.

Figure 3 -. Identification of SNPs in the structure of the TLR8 gene. In the graph the higher frequency of nucleotides is represented in black with synonymous and non-synonymous occurrences in two populations of manatees. The cartoon structure is represented by exon 1 (red). Rectangles represent LRRs (1-21), LRR-CT, trans-membrane (TM) and intracellular (TM) domains.