Species Specificity in Major Urinary Proteins by Parallel Evolution

Abstract

Species-specific chemosignals, pheromones, regulate social behaviors such as aggression, mating, pup-suckling, territory establishment, and dominance. The identity of these cues remains mostly undetermined and few mammalian pheromones have been identified. Genetically-encoded pheromones are expected to exhibit several different mechanisms for coding 1) diversity, to enable the signaling of multiple behaviors, 2) dynamic regulation, to indicate age and dominance, and 3) species-specificity. Recently, the major urinary proteins (Mups) have been shown to function themselves as genetically-encoded pheromones to regulate species-specific behavior. Mups are multiple highly related proteins expressed in combinatorial patterns that differ between individuals, gender, and age; which are sufficient to fulfill the first two criteria. We have now characterized and fully annotated the mouse Mup gene content in detail. This has enabled us to further analyze the extent of Mup coding diversity and determine their potential to encode species-specific cues.Our results show that the mouse Mup gene cluster is composed of two subgroups: an older, more divergent class of genes and pseudogenes, and a second class with high sequence identity formed by recent sequential duplications of a single gene/pseudogene pair. Previous work suggests that truncated Mup pseudogenes may encode a family of functional hexapeptides with the potential for pheromone activity. Sequence comparison, however, reveals that they have limited coding potential. Similar analyses of nine other completed genomes find Mup gene expansions in divergent lineages, including those of rat, horse and grey mouse lemur, occurring independently from a single ancestral Mup present in other placental mammals. Our findings illustrate that increasing genomic complexity of the Mup gene family is not evolutionarily isolated, but is instead a recurring mechanism of generating coding diversity consistent with a species-specific function in mammals.

Reintroducing domesticated wild mice to sociality induces adaptive transgenerational effects on MUP expression

“…Because MUPs represent substantial investment in excreted protein, we hypothesized that increased mating success and decreased survival in promiscuous-line males could be associated with up-regulated MUP expression. Urine collected from fourth-generation, individually housed adult males following the testosterone assay revealed that promiscuous-line males had higher MUP expression than monogamous-line males ( To identify specific up-regulated Mup loci in promiscuous-line males, we used reverse transcription quantitative qPCR (rt-qPCR) with nine primer sets from published studies that amplify most Mup transcripts (19,29) (Table S1). Because of extremely high sequence identity, some primer pairs were able to discriminate only subsets of paralogous Mup loci (29).…”

“…Urine collected from fourth-generation, individually housed adult males following the testosterone assay revealed that promiscuous-line males had higher MUP expression than monogamous-line males ( To identify specific up-regulated Mup loci in promiscuous-line males, we used reverse transcription quantitative qPCR (rt-qPCR) with nine primer sets from published studies that amplify most Mup transcripts (19,29) (Table S1). Because of extremely high sequence identity, some primer pairs were able to discriminate only subsets of paralogous Mup loci (29). Total sequence identity of the Mup locus in our congenic wild mice with that of reference strains (C57 and BALB/c) is unknown; however, sequence analysis of PCR products confirmed amplification of similar Mups in our mice.…”

“…Mups in house mice cover an approximately 2 megabase region of chromosome four and are interspersed with many endogenous retrotransposons (29,50). Epigenetic gene regulation often involves interactions with the silencing of neighboring transposable elements and includes response to environmental stressors (51) and transgenerational inheritance (8).…”

Mouse urinary peptides provide a molecular basis for genotype discrimination by nasal sensory neurons

“…We have identified a novel family of MHC-independent peptides that differ in strains by single aminoacid exchanges, and we show for the first time (see Supplementary Note 1) that a bona fide MHC peptide ligand exists in urine in an MHC-dependent manner at biologically relevant concentrations. Hence, the emerging picture is a complex scenario in which multiple peptide families together with previously characterized MUPs 35,49,50 , formylated and maternally inherited peptides (not yet shown to exist in urine) 25 and possibly other yet undiscovered ligand families link the genotype of an individual with nasal chemoreception mechanisms. Future research should examine the contribution of these peptides to genotype discrimination in diverse behavioural contexts, but it will be essential to select urine samples for such experiments with care.…”

The existence of species rests on a metastable equilibrium between inbreeding and outbreeding

“…Furthermore, in an extremely recent paper, the group of Jane Hurst actually characterises Darcin, an invariant urinary protein found in the urine of male mice, which behaves as a pheromone by inducing contact-dependent imprinting of females to prefer the males harbouring the other smells found in that urine [98]. The observation that diverse MUP complexes undergo parallel evolution in different species suggests that polymorphic MUPs, as well as other polymorphic factors [99], may play an important role in regulating the mating behaviour in many species [100], which may call for revisiting some of the results obtained regarding the pivotal role of the MHC in regulating the degree of inbreeding between individuals in vertebrate species, including fish.…”