Divergent Selection of Pattern Recognition Receptors in Mammals with Different Ecological Characteristics

Abstract

Pattern recognition receptors (PRRs) are specialized receptors that represent a key component of the host innate immune system. Whether molecular evolutionary history of different PRR classes have involved different genetic mechanisms underlying diverse pathogen environment in mammals, and whether distinct ecology of mammals may have imposed divergent selective pressures on the evolution of the PRRs, remained unknown. To test these hypotheses, we investigated the characterization of 20 genes belonging to four PRR classes in mammals. Evidence of positive selection was found in most (17 of 20) PRR genes examined, and most positively selected sites (84%) undergoing radical changes were found to fall in important functional regions, consistent with the co-evolutionary dynamics between the hosts and their microbial counterparts. We found different evolutionary patterns in different PRR classes, with the highest level of positive selection in C-type lectin receptor (CLR) family, suggesting that the capability of CLRs in response to a wide variety of ligands might explain their malleability to selection pressures. Tests using branch models that partitioned the data along habitat and social behavior found significant evidence of divergent selective pressures of PRRs among mammalian groups. Interestingly, species-specific evolution was detected on RIG-I-like helicase genes (RLRs) in cetaceans, suggesting that RLRs might play a critical role in the defense against widespread marine RNA viruses during their divergence and radiation into marine habitats. This study provides a comprehensive look at the evolutionary patterns and implications of mammalian PRRs, and highlights the importance of ecological influences in molecular adaptation.

Impact of Historic Migrations and Evolutionary Processes on Human Immunity

“…The human genome presents more than 5000 genetic loci with traces of selective pressure [2]. This group includes more than 300 immune-related genes with functional variations between populations, which are probably behind the variability of responses to immune-related diseases reported nowadays [3,4]. Besides natural selection, other evolutionary mechanisms, such as genetic drift, greatly influence the frequencies of the genetic variants found within diverse populations throughout the world [5] (Box 1 and Figure 1).…”

Divergent Evolution of TRC Genes in Mammalian Niche Adaptation

“…Both of these two mechanisms were important for the fitness of mammals in their specific habitat and sociality. Evidences of habitat transition driving the evolution of immune-related genes have been identified on many innate immunity genes (2, 51). Particularly, most researches on the immune-related genes were carried out to explore the potential mechanism for the immunity adaption of cetaceans during their habitat transition (3, 52).…”

“…There was a view that innate immune systems were the key line of defense in their coexistence with viruses (5). Many pattern recognition receptor genes (TLRs and RLRs) that constitute the first line of defense of organisms were subjected to positive selection in bats, indicating their enhancement of capacity in inflammasome assembly during viral infections (2). Specially, antiviral defenses by constitutively expressed IFN-α and expanded and diversified numerous antiviral loci provided them the ability to coexist with viruses (65, 66).…”

“…Studies on the relationships between ecological factors and variations of immune genes have emerged in recent years. Recently, molecular adaptations in pattern recognition receptors (PRRs) were highlighted among mammals with diverse niches (habitat, diet, and living pattern) (2). Cetaceans are good models to assess the evolutionary changes of habitat transitions from land to water.…”

Recent Advances In Nutritional Sciences: An Overview Of Glycans And MiRNAs

“…The innate immune system is the first line of host defence of both humans and animals and is present in the gut [224]. The function of the innate immune is to recognize pathogen-associated molecular patterns (PAMPs) or microbial-associated molecular patterns (MAMPs) [228], using a variety of host receptors called pattern recognition receptors (PRRs) [229,230]. Interestingly, many of the PRRs are lectins [120,122] and interact with foreign or endogenous glycans.…”