The importance of olfactory receptors
adaptation, alpha-mating factor, amino acid, atoms to ecosystems, behaviors, chromosomal rearrangements, ecological, experience-dependent, feedback loops, fertilization, GnRH, LH, life cycle, microRNA / messenger RNA, nutrient-dependent, odor, olfactory receptor, olfactory/pheromonal, pheromonal, pheromone, pheromone-controlled, plasticity, protein-folding, receptor-mediated, reproduction, sex differences, signaling, thermodynamic, yeast
By ALEX STONE
Excerpt: “I’ve been arguing for the importance of these receptors for years,” said Dr. Hatt, who calls himself an ambassador of smell, and whose favorite aromas are basil, thyme and rosemary. “It was a hard fight.”
Excerpt: “…these results indicate that hOR17-4 functions in human sperm chemotaxis and may be a critical component of the fertilization process.”
Wang, Wysocki, and Gold (1993) showed that repeat exposure to androstenone and to isovaleric acid can induce olfactory receptor sensitivity in mice via stimulus-induced plasticity in olfactory receptor cells. Thus, it appears that olfactory sensitivity to at least some odors can vary from no sensitivity to markedly heightened sensitivity during the life cycle and that some sex differences in the organization of olfactory sensitivity can occur.
In this regard it seems important to emphasize that chemosensory communication is ubiquitous throughout life among species from single celled yeasts to primates, including humans (see for review Kohl and Francoeur, 1995). Chemical stimuli, odors, including pheromones, are essential components of reproductive sexual behavior in most, if not all, species. Pheromonal communication has been seen to elicit physiological and behavioral changes that benefit both male and female individuals and, in humans, these olfactory sensations seem to exert their influence whether or not an individual is conscious of odor detection.
Evolutionary conservation, both of pheromonal communication and its importance to behavior, is indicated by the involvement of a key mammalian reproductive hormone. For instance, a yeast pheromone, the alpha-mating factor, is very similar in structure to mammalian gonadotropic releasing hormone (GnRH). When injected into rats, this chemical binds to pituitary GnRH receptors and brings about the release of LH. Loumaye, Thorner, and Catt (1982) note: “GnRH and the yeast alpha-mating factor appear to represent a highly conserved effector system which includes the peptide ligand, the cell-surface receptor, and the physiological regulation of reproductive function” (p. 1325).
Excerpt: ” Indications that GnRH peptide plays an important role in the control of sexual behaviors suggest that pheromone effects on these behaviors might also involve GnRH neurons.”
Excerpt: “Olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans (Keller et al., 2007; Kohl, 2007; Villarreal, 2009; Vosshall, Wong, & Axel, 2000).”
Excerpt: “… the model represented here is consistent with what is known about the epigenetic effects of ecologically important nutrients and pheromones on the adaptively evolved behavior of species from microbes to man. Minimally, this model can be compared to any other factual representations of epigenesis and epistasis for determination of the best scientific ‘fit’.”
Abstract: This atoms to ecosystems model of ecological adaptations links nutrient-dependent epigenetic effects on base pairs and amino acid substitutions to pheromone-controlled changes in the microRNA / messenger RNA balance and chromosomal rearrangements. The nutrient-dependent pheromone-controlled changes are required for the thermodynamic regulation of intracellular signaling, which enables biophysically constrained nutrient-dependent protein folding; experience-dependent receptor-mediated behaviors, and organism-level thermoregulation in ever-changing ecological niches and social niches. Nutrient-dependent pheromone-controlled ecological, social, neurogenic and socio-cognitive niche construction are manifested in increasing organismal complexity in species from microbes to man. Species diversity is a biologically-based nutrient-dependent morphological fact and species-specific pheromones control the physiology of reproduction. The reciprocal relationships of species-typical nutrient-dependent morphological and behavioral diversity are enabled by pheromone-controlled reproduction. Ecological variations and biophysically constrained natural selection of nutrients cause the behaviors that enable ecological adaptations. Species diversity is ecologically validated proof-of-concept. Ideas from population genetics, which exclude ecological factors, are integrated with an experimental evidence-based approach that establishes what is currently known. This is known: Olfactory/pheromonal input links food odors and social odors from the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man during their development.
Excerpt: “Our results clearly demonstrate that postnatal odorant exposure induces molecular and cellular remodeling in olfactory sensory neurons at the cellular level. Through this plasticity, OSNs can adapt to their environment.”
OSNs, like odor receptors in the cells of tissues in organs and organ systems of organisms that manifest their ability to ecological adapt link the experience-dependent de novo creation of olfactory receptor genes from the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man via conserved molecular mechanisms of RNA-mediated events that we detailed in our 1996 Hormones and Behavior review.
The olfactory/pheromonal link from the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man It is not going to become any clearer. We already know the link is experience dependent and that RNA-directed DNA methylation is the link to RNA-mediated amino acid substitutions that differentiate all cell types in all individuals of all species.