Chemical Senses最新文献

Across the animal kingdom, a remarkable diversity of chemoreceptors has evolved, reflecting the ecological and evolutionary pressures that shape species-specific sensory demands. Insects, the most biodiverse class of animals, play crucial roles in ecosystems and have an extensive chemosensory repertoire. At the heart of insect gustation lie the gustatory receptors (GRs), a large and remarkably diverse family of proteins characterized by their seven-transmembrane domain structure and tetrameric stoichiometry. These receptors are phylogenetically distinct from the taste receptors present in most other animal groups, including mammals. Functionally, GRs operate as ligand-gated cation channels. Upon binding to specific chemical compounds (tastants), these receptors undergo conformational changes that lead to the opening of ion-conducting channels in the neuronal membrane, ultimately triggering neuronal activation and initiating the perception of taste. Recent advancements in structural biology, particularly the use of cryo-electron microscopy, have enabled the visualization of the three-dimensional structure of several insect GRs that detect sugars. These structures, in unbound and ligand-bound states, have begun to reveal the principles of sugar recognition and discrimination. Here, we highlight recent advances in our understanding of insect GRs.

Lyncodon patagonicus (Patagonian weasel), Galictis cuja (lesser grison), and Galictis vittata (greater grison) are the only extant species of Lyncodontini, a relatively poorly known Neotropical tribe of the mustelid subfamily Ictonychinae within the mammalian order Carnivora. Here, we report molecular evidence indicating that the TAS1R1-TAS1R3 umami (savory) taste receptor lost its function in the Lyncodontini's stem lineage (∼3 to 9.5 million years ago) and is therefore nonfunctional in all crown Lyncodontini. This finding is unexpected and intriguing because all extant Lyncodontini apparently need this receptor (they are terrestrial carnivores with diets high in umami-eliciting compounds, including purine 5'-monophosphate ribonucleotides, the main agonists of TAS1R1-TAS1R3 in carnivorans). We argue that the common ancestor of extant Lyncodontini that first lost TAS1R1-TAS1R3 function was semiaquatic and predated mainly on fish and/or aquatic invertebrates (tissues of living or recently dead fish and aquatic invertebrates are low in purine 5'-monophosphate ribonucleotides). This hypothesis is consistent with the idea that loss of taste receptor function is caused by feeding specializations that restrict access to the compounds that a particular receptor detects. Our hypothesis effectively suggests a prolonged semiaquatic episode in the evolutionary history of the Lyncodontini's stem lineage because loss of TAS1R1-TAS1R3 function is achieved by a stochastic process continuing over evolutionary time. Whether the extant Lyncodontini evolved a mechanism to compensate for the loss of TAS1R1-TAS1R3 function is currently unknown and requires further research.

Congenital blindness affects olfactory function depending on the developmental stage. However, when studying the ontogeny of olfactory abilities, not all behaviors are expressed at every age making the longitudinal comparisons difficult. Odor-evoked respiratory responses, which are unlearned and do not require complex motor coordination, may serve as sensitive measures of olfactory abilities throughout ontogeny. Using a noninvasive measure of respiration in an olfactory perceptual paradigm, we assessed odor-evoked respiratory responses in a model of congenital blindness at 3 ages, infant, juvenile, and adult, in the same mice and in both males and females. We demonstrated the differential outcome of 2 respiratory parameters (i.e. frequency and amplitude) in a mouse model of congenital blindness. We showed that blind mice have similar olfactory abilities than sighted mice throughout ontogeny but display enhanced sniffing frequency and amplitude, starting at the juvenile age for the latter one, that may help them better explore their environment. We also demonstrated that respiratory frequency is a robust index of age and of olfactory detection, habituation, and discrimination at all ages. On the other side, the respiratory amplitude does not provide a proxy of olfactory performance at all ages, however, it does highlight differences between sexes and phenotypes associated with visual deprivation. To conclude, our data highlight that respiratory parameters can be used as a complementary approach to assess olfactory performance throughout development and provide an index of olfactory plasticity.