The evolutionary history of the SAL1 gene family in eutherian mammals

Abstract

BackgroundSAL1 (salivary lipocalin) is a member of the OBP (Odorant Binding Protein) family and is involved in chemical sexual communication in pig. SAL1 and its relatives may be involved in pheromone and olfactory receptor binding and in pre-mating behaviour. The evolutionary history and the selective pressures acting on SAL1 and its orthologous genes have not yet been exhaustively described. The aim of the present work was to study the evolution of these genes, to elucidate the role of selective pressures in their evolution and the consequences for their functions.ResultsHere, we present the evolutionary history of SAL1 gene and its orthologous genes in mammals. We found that (1) SAL1 and its related genes arose in eutherian mammals with lineage-specific duplications in rodents, horse and cow and are lost in human, mouse lemur, bushbaby and orangutan, (2) the evolution of duplicated genes of horse, rat, mouse and guinea pig is driven by concerted evolution with extensive gene conversion events in mouse and guinea pig and by positive selection mainly acting on paralogous genes in horse and guinea pig, (3) positive selection was detected for amino acids involved in pheromone binding and amino acids putatively involved in olfactory receptor binding, (4) positive selection was also found for lineage, indicating a species-specific strategy for amino acid selection.ConclusionsThis work provides new insights into the evolutionary history of SAL1 and its orthologs. On one hand, some genes are subject to concerted evolution and to an increase in dosage, suggesting the need for homogeneity of sequence and function in certain species. On the other hand, positive selection plays a role in the diversification of the functions of the family and in lineage, suggesting adaptive evolution, with possible consequences for speciation and for the reinforcement of prezygotic barriers.

New genes as drivers of phenotypic evolution

“…For example, INSL4 is involved in placental and fetal growth in catarrhine primates 62 . Other duplication events that have been implicated in mammalian reproduction-related phenotypes include the diversification of fetus-expressed globin genes 63 , the evolution of milk casein proteins 64 and the lineage-specific expansion of SAL1 genes that are involved in pheromone and odorant binding, which is in turn related to the evolution of species-specific mate choice and sexual behaviour 65 . Furthermore, the artificial selection for dogs with various morphologies in recent human history gave rise to an extremely young functional gene in the fibroblast growth factor family, FGF4 , which is responsible for the selected chondrodysplasia morphology 66 .…”

Proteomic Analysis of Pig (Sus scrofa) Olfactory Soluble Proteome Reveals O-Linked-N-Acetylglucosaminylation of Secreted Odorant-Binding Proteins

“…Three VEG and five SAL isoforms were identified in porcine saliva ( 47 ), and four VEG isoforms in human saliva ( 46 ). The human saliva did not contain any SAL isoform, as the encoding gene SAL1 is a pseudogene in this species ( 48 ). But in both cases, these isoforms are not the major proteins (<1% of the total spots).…”

Rapid Evolution of Beta-Keratin Genes Contribute to Phenotypic Differences That Distinguish Turtles and Birds from Other Reptiles

“…Following duplication, genes may be subject to adaptive pressures that reflect species-specific biology, they may be more prone to random genetic drift, or they may be silenced and undergo nonfunctionalization. Among gene duplicates that appear to have been preferentially fixed owing to their novel, beneficial, function are those that encode visual pigments in insects and vertebrates (Yuan et al 2010; Rennison et al 2012), venoms in mollusks (Chang and Duda 2012), olfactory and gustatory receptors in insects (Robertson and Wanner 2006; McBride 2007), reptiles, and mammals (Meslin et al 2011; Jiang et al 2012), leukocyte receptor in human, mouse, and chicken, and the Hox gene family of transcription factors that regulate animal development (Barten et al 2001; Nikolaidis et al 2005; Pearson et al 2005; Laun et al 2006). …”