Sensing the chemical warnings present in the environment is essential for species survival. In mammals, this form of danger communication occurs via the release of natural predator scents that can involuntarily warn the prey or by the production of alarm pheromones by the stressed prey alerting its conspecifics. Although we previously identified the olfactory Grueneberg ganglion as the sensory organ through which mammalian alarm pheromones signal a threatening situation, the chemical nature of these cues remains elusive. We here identify, through chemical analysis in combination with a series of physiological and behavioral tests, the chemical structure of a mouse alarm pheromone. To successfully recognize the volatile cues that signal danger, we based our selection on their activation of the mouse olfactory Grueneberg ganglion and the concomitant display of innate fear reactions. Interestingly, we found that the chemical structure of the identified mouse alarm pheromone has similar features as the sulfur-containing volatiles that are released by predating carnivores. Our findings thus not only reveal a chemical Leitmotiv that underlies signaling of fear, but also point to a double role for the olfactory Grueneberg ganglion in intraspecies as well as interspecies communication of danger.olfaction | animal communication | behavior | calcium imaging

In response to various pathological stresses, the heart undergoes a pathological remodeling process that is associated with cardiomyocyte hypertrophy. Because cardiac hypertrophy can progress to heart failure, a major cause of lethality worldwide, the intracellular signaling pathways that control cardiomyocyte growth have been the subject of intensive investigation. It has been known for more than a decade that the small molecular weight GTPase RhoA is involved in the signaling pathways leading to cardiomyocyte hypertrophy. Although some of the hypertrophic pathways activated by RhoA have now been identified, the identity of the exchange factors that modulate its activity in cardiomyocytes is currently unknown. In this study, we show that AKAP-Lbc, an A-kinase anchoring protein (AKAP) with an intrinsic Rho-specific guanine nucleotide exchange factor activity, is critical for activating RhoA and transducing hypertrophic signals downstream of ␣1-adrenergic receptors (ARs). In particular, our results indicate that suppression of AKAP-Lbc expression by infecting rat neonatal ventricular cardiomyocytes with lentiviruses encoding AKAP-Lbcspecific short hairpin RNAs strongly reduces both ␣1-AR-mediated RhoA activation and hypertrophic responses. Interestingly, ␣1-ARs promote AKAP-Lbc activation via a pathway that requires the ␣ subunit of the heterotrimeric G protein G12. These findings identify AKAP-Lbc as the first Rho-guanine nucleotide exchange factor (GEF) involved in the signaling pathways leading to cardiomyocytes hypertrophy.cardiac hypertrophy ͉ Rho GTPase ͉ G protein-coupled receptor

To investigate their role in receptor coupling to G q , we mutated all basic amino acids and some conserved hydrophobic residues of the cytosolic surface of the ␣ 1b -adrenergic receptor (AR) GPCRs are structurally characterized by seven transmembrane ␣-helices connected by alternating extracellular (e) and intracellular (i) loops. While the extracellular portion of these receptors is primarily involved in ligand binding, the cytosolic loops mediate the interaction of the receptors with a number of signaling and regulatory proteins, including G proteins, arrestins, and G protein-coupled receptor kinases (reviewed in Ref..2).Evidence suggests that a conformational adjustment within the helical bundle of the receptor underlies the process of agonist-induced activation of GPCRs (reviewed in Ref.3). The current hypothesis is that the transition from the inactive (R) to active (R*) state of a GPCR results in receptor interaction with, and activation of, a G protein. Thus a GPCR-mediated biological response involves a series of events (i.e. receptor activation, receptor-G protein interaction, and receptor-induced G protein activation) for which a detailed mechanism still remains elusive at the molecular level. Although residues located in the helical bundle and at the boundary between the membrane and the cytosol may play a role in the "conformational switch" underlying receptor activation, amino acids in the intracellular loops are believed to be more directly involved in receptor-G protein interaction and/or receptor-induced G protein activation. The combination of these two latter events, which cannot be unequivocally separated experimentally, is generally indicated with the term of receptor-G protein coupling.We have previously provided evidence that the negatively and positively charged amino acids of the conserved DRY motif at the cytosolic end of helix 3 play a key role in the activation process of the ␣ 1b -AR (4 -6). Following a combination of experimental and computer-simulated mutagenesis of the ␣ 1b -AR, we have hypothesized that protonation of the aspartate (Asp 142 ) and a shift of the arginine (Arg 143 ) out of a conserved "polar pocket" are crucial steps in the transition of the receptor from the inactive (R) to active (R*) state (4 -6).Several studies have tried to identify the amino acids of different GPCRs involved in G protein coupling at both experimental (as reviewed in Ref.2) and theoretical levels (7-10). The majority of these studies indicate that sequences in the i2 loop as well as in the N and C termini of the i3 loop play an

We provide the first evidence that point mutations can constitutively activate the L L 1 -adrenergic receptor (AR). Leucine 322 of the L L 1 -AR in the C-terminal portion of its third intracellular loop was replaced with seven amino acids (I, T, E, F, C, A and K) differing in their physico-chemical properties. The L L 1 -AR mutants expressed in HEK-293 cells displayed various levels of constitutive activity which could be partially inhibited by some beta-blockers. The results of this study might have interesting implications for future studies aiming at elucidating the activation process of the L L 1 -AR as well as the mechanism of action of beta-blockers.z 1999 Federation of European Biochemical Societies.

In the mouse, the Grueneberg ganglion (GG) is an olfactory subsystem implicated both in chemo- and thermo-sensing. It is specifically involved in the recognition of volatile danger cues such as alarm pheromones and structurally-related predator scents. No evidence for these GG sensory functions has been reported yet in other rodent species. In this study, we used a combination of histological and physiological techniques to verify the presence of a GG and investigate its function in the rat, hamster, and gerbil comparing with the mouse. By scanning electron microscopy (SEM) and transmitted electron microscopy (TEM), we found isolated or groups of large GG cells of different shapes that in spite of their gross anatomical similarities, display important structural differences between species. We performed a comparative and morphological study focusing on the conserved olfactory features of these cells. We found fine ciliary processes, mostly wrapped in ensheating glial cells, in variable number of clusters deeply invaginated in the neuronal soma. Interestingly, the glial wrapping, the amount of microtubules and their distribution in the ciliary processes were different between rodents. Using immunohistochemistry, we were able to detect the expression of known GG proteins, such as the membrane guanylyl cyclase G and the cyclic nucleotide-gated channel A3. Both the expression and the subcellular localization of these signaling proteins were found to be species-dependent. Calcium imaging experiments on acute tissue slice preparations from rodent GG demonstrated that the chemo- and thermo-evoked neuronal responses were different between species. Thus, GG neurons from mice and rats displayed both chemo- and thermo-sensing, while hamsters and gerbils showed profound differences in their sensitivities. We suggest that the integrative comparison between the structural morphologies, the sensory properties, and the ethological contexts supports species-dependent GG features prompted by the environmental pressure.