Sour Ageusia in Two Individuals Implicates Ion Channels of the ASIC and PKD Families in Human Sour Taste Perception at the Anterior Tongue

BACKGROUND:The perception of sour taste in humans is incompletely understood at the receptor cell level. We report here on two patients with an acquired sour ageusia. Each patient was unresponsive to sour stimuli, but both showed normal responses to bitter, sweet, and salty stimuli. METHODS AND FINDINGS:Lingual fungiform papillae, containing taste cells, were obtained by biopsy from the two patients, and from three sour-normal individuals, and analyzed by RT-PCR. The following transcripts were undetectable in the patients, even after 50 cycles of amplification, but readily detectable in the sour-normal subjects: acid sensing ion channels (ASICs) 1a, 1beta, 2a, 2b, and 3; and polycystic kidney disease (PKD) channels PKD1L3 and PKD2L1. Patients and sour-normals expressed the taste-related phospholipase C-beta2, the delta-subunit of epithelial sodium channel (ENaC) and the bitter receptor T2R14, as well as beta-actin. Genomic analysis of one patient, using buccal tissue, did not show absence of the genes for ASIC1a and PKD2L1. Immunohistochemistry of fungiform papillae from sour-normal subjects revealed labeling of taste bud cells by antibodies to ASICs 1a and 1beta, PKD2L1, phospholipase C-beta2, and delta-ENaC. An antibody to PKD1L3 labeled tissue outside taste bud cells. CONCLUSIONS:These data suggest a role for ASICs and PKDs in human sour perception. This is the first report of sour ageusia in humans, and the very existence of such individuals ("natural knockouts") suggests a cell lineage for sour that is independent of the other taste modalities

The importance of the altricial – precocial spectrum for social complexity in mammals and birds:A review

Various types of long-term stable relationships that individuals uphold, including cooperation and competition between group members, define social complexity in vertebrates. Numerous life history, physiological and cognitive traits have been shown to affect, or to be affected by, such social relationships. As such, differences in developmental modes, i.e. the ‘altricial-precocial’ spectrum, may play an important role in understanding the interspecific variation in occurrence of social interactions, but to what extent this is the case is unclear because the role of the developmental mode has not been studied directly in across-species studies of sociality. In other words, although there are studies on the effects of developmental mode on brain size, on the effects of brain size on cognition, and on the effects of cognition on social complexity, there are no studies directly investigating the link between developmental mode and social complexity. This is surprising because developmental differences play a significant role in the evolution of, for example, brain size, which is in turn considered an essential building block with respect to social complexity. Here, we compiled an overview of studies on various aspects of the complexity of social systems in altricial and precocial mammals and birds. Although systematic studies are scarce and do not allow for a quantitative comparison, we show that several forms of social relationships and cognitive abilities occur in species along the entire developmental spectrum. Based on the existing evidence it seems that differences in developmental modes play a minor role in whether or not individuals or species are able to meet the cognitive capabilities and requirements for maintaining complex social relationships. Given the scarcity of comparative studies and potential subtle differences, however, we suggest that future studies should consider developmental differences to determine whether our finding is general or whether some of the vast variation in social complexity across species can be explained by developmental mode. This would allow a more detailed assessment of the relative importance of developmental mode in the evolution of vertebrate social systems

RT-PCR and genomic analysis of acid sensing ion channel (ASIC) gene expression for sour-ageusic Patient 8689.

<p>The patient expresses housekeeping and taste-related genes but ASIC transcripts are undetectable even after 50 cycles of amplification, and for ASICs 1a and 1β this is not the result of a loss of the <i>ASIC1</i> gene. Lane identifications: (A) 100 bp DNA marker with the brightest band being 500 bp; (B) Transcript of β-actin; (C–G) Transcripts of, respectively, ASICs 1a, 1β, 2a, 2b and 3; (H) Transcript of δ-ENaC; (I) 1 kb DNA marker; (J) ASIC1a, full coding sequence; (K) genomic DNA amplified with primer pair ASICMCF1 and ASICMCR1 (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007347#pone-0007347-t001" target="_blank">Table 1</a>); and (L) genomic DNA amplified with primer pair HASIC3 and HASIC4 (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007347#pone-0007347-t001" target="_blank">Table 1</a>). RT-PCR was performed with cDNA from fungiform papillae (B–H and J), but only the data for the tubes containing reverse transcriptase are presented. No products were detected in the tubes lacking reverse transcriptase. Genomic analysis (K, L) was performed using buccal tissue. Individual amplification reactions were performed for each named molecular target and the data are shown in collated form. Identities of all amplification products were confirmed by sequencing.</p