Detection Of Social Cues Research Articles

Ecological Trait Differences Are Associated with Gene Expression in the Primary Visual Cortex of Primates

Primate species differ drastically from most other mammals in how they visually perceive their environments, which is particularly important for foraging, predator avoidance, and detection of social cues. Background/Objectives: Although it is well established that primates display diversity in color vision and various ecological specializations, it is not understood how visual system characteristics and ecological adaptations may be associated with gene expression levels within the primary visual cortex (V1). Methods: We performed RNA-Seq on V1 tissue samples from 28 individuals, representing 13 species of primates, including hominoids, cercopithecoids, and platyrrhines. We explored trait-dependent differential expression (DE) by contrasting species with differing visual system phenotypes and ecological traits. Results: Between 4–25% of genes were determined to be differentially expressed in primates that varied in type of color vision (trichromatic or polymorphic di/trichromatic), habitat use (arboreal or terrestrial), group size (large or small), and primary diet (frugivorous, folivorous, or omnivorous). Conclusions: Interestingly, our DE analyses revealed that humans and chimpanzees showed the most marked differences between any two species, even though they are only separated by 6–8 million years of independent evolution. These results show a combination of species-specific and trait-dependent differences in the evolution of gene expression in the primate visual cortex.

A New Class of Chemosensory Receptors

Members of a large family of odorant receptors found in olfactory sensory neurons (OSNs) in the main olfactory epithelium detect volatile odorants. Liberles and Buck prepared cDNA and then performed quantitative polymerase chain reaction (qPCR) to search mouse OSNs for G protein-coupled receptors (GPCRs) that had not been implicated previously in taste, odor, or pheromone detection. They identified two members of the trace amine-associated receptor (TAAR) family of GPCRs, which have been hypothesized to act in the brain as receptors for biogenic trace amines, such as tyramine and β-phenylethylamine. Further analysis with qPCR and in situ hybridization indicated that eight of nine mouse taar genes were expressed in olfactory epithelium and that, like odorant receptors, different TAARs are found in different OSNs. TAARs did not appear to be coexpressed with olfactory receptors but were coexpressed with Gα olf , the family of heterotrimeric guanine nucleotide-binding protein (G protein) α subunits through which odorant receptors signal. Individual mouse or human TAARs were coexpressed with an adenosine 3′,5′-monophosphate (cAMP)-dependent reporter gene in HEK293 cells that were cultured with potential ligands. Three mouse TAARs responded to volatile amines present in mouse urine: One detected β-phenylethylamine, which is associated with stress, and two others detected substances present in greater abundance in male than female urine. Thus, the authors propose that the TAARs may represent a family of chemosensory receptors that are functionally distinct from odorant receptors and appear to be associated with the detection of social cues. Ngai discusses implications of the research. S. D. Liberles, L. B. Buck, A second class of chemosensory receptors in the olfactory epithelium. Nature 442 , 645-650 (2006). [PubMed] J. Ngai, An extra dimension to olfaction. Nature 442 , 637-638 (2006). [PubMed]

A second class of chemosensory receptors in the olfactory epithelium

The mammalian olfactory system detects chemicals sensed as odours as well as social cues that stimulate innate responses. Odorants are detected in the nasal olfactory epithelium by the odorant receptor family, whose approximately 1,000 members allow the discrimination of a myriad of odorants. Here we report the discovery of a second family of receptors in the mouse olfactory epithelium. Genes encoding these receptors, called 'trace amine-associated receptors' (TAARs), are present in human, mouse and fish. Like odorant receptors, individual mouse TAARs are expressed in unique subsets of neurons dispersed in the epithelium. Notably, at least three mouse TAARs recognize volatile amines found in urine: one detects a compound linked to stress, whereas the other two detect compounds enriched in male versus female urine-one of which is reportedly a pheromone. The evolutionary conservation of the TAAR family suggests a chemosensory function distinct from odorant receptors. Ligands identified for TAARs thus far suggest a function associated with the detection of social cues.