Variation in selection constraints on teleost TLRs with emphasis on their repertoire in the Walking catfish, Clarias batrachus

Abstract

The high degree of conservation of toll-like receptors (TLRs), and yet their subtle variations for better adaptation of species in the host–pathogen arms race make them worthy candidates for understanding evolution. We have attempted to track the trend of TLR evolution in the most diverse vertebrate group—teleosts, where Clarias batrachus was given emphasis, considering its traits for terrestrial adaptation. Eleven C. batrachus TLRs (TLR1, 2, 3, 5, 7, 8 9, 13, 22, 25, 26) were identified in this study which clustered in proximity to its Siluriformes relative orthologues in the phylogenetic analysis of 228 TLRs from 25 teleosts. Ten TLRs (TLR1, 2, 3, 5, 7, 8 9, 13, 21, 22) with at least 15 member orthologues for each alignment were processed for selection pressure and coevolutionary analysis. TLR1, 7, 8 and 9 were found to be under positive selection in the alignment-wide test. TLR1 also showed maximum episodic diversification in its clades while the teleost group Eupercaria showed the maximum divergence in their TLR repertoire. Episodic diversification was evident in C. batrachus TLR1 and 7 alignments. These results present a strong evidence of a divergent TLR repertoire in teleosts which may be contributing towards species-specific variation in TLR functions.

Genome-wide investigation and expression analysis of TLR gene family reveals its immune role in Vibrio tolerance challenge of Manila clam

“…TLR4, TLR5, TLR7, TLR13 genes are generally highly expressed in individuals with resistance to V. anguillarum infection. Diversity of TLR genes has also been reported in teleosts, comparative genomics studies have attributed this trend of divergence in teleost lineage to enhanced molecular evolutionary rates of nucleotide and protein coding sequences and higher rate of gain and loss of cis-regulatory elements that consequently alters morphology or function [ 50 , 51 ]. For the different antibacterial effects of TLR family members, the study of mice deficient in each TLR have demonstrated that each TLR has a distinct function in terms of PAMP recognition and immune responses [11] .…”

Riding the wave of innovation: immunoinformatics in fish disease control

“…Recent studies on fish TLRs have concentrated on identifying individual TLR members in diverse teleost fish species such as TLR7 and TLR8 in Barbel chub ( Squaliobarbus curriculus ) ( Jin et al, 2018 ), TLR21, TLR22, and TLR25 in Dabry’s sturgeon ( Acipenser dabryanus ) ( Qi et al, 2018 ), TLR1-TLR3, TLR5, TLR7-TLR9. TLR13, TLR22, TLR25, and TLR26 in Walking catfish ( Clarias batrachus ) ( Priyam et al, 2020 ). Furthermore, researchers have also examined what occurs when a pathogenic bacterium, virus, or ligand is used as a stimulator, with regard to expression profiles and signalling cascade genes ( Jiang et al, 2020 ; Muduli et al, 2021 ; Wang et al, 2021 ).…”