Biomedical subjects

Lynne D Houck

Publications and source records attributed to Lynne D Houck.

6 recordsLinked to original sources

PubMed2006

In situ localization of plethodontid courtship pheromone mRNA in formalin-fixed tissue.

Male plethodontid salamanders produce courtship pheromones that increase female receptivity. Three protein components of the courtship pheromone cocktail have been characterized in the mental gland of Plethodon shermani, the red-legged salamander: plethodontid receptivity factor (PRF), plethodontid modulating factor (PMF), and sodefrin precursor-like factor (SPF). In this study, a streamlined in situ hybridization (ISH) protocol, employing a biotinylated oligonucleotide probe, is used to visualize the sites of pheromone expression in formalin-fixed paraffin-embedded P. shermani mental gland and post-cloacal tail tissue. Results corroborate previous RT-PCR studies on pheromone expression. PRF and PMF are highly expressed in P. shermani mental gland, while SPF expression is more variable. None of the tested pheromones is expressed in dorsal or ventral tail glands. The reported protocol is simple, rapid, and effective, allowing visualization of high-copy mRNA transcript in formalin-fixed tissue.

Animals↗

PubMed2006

Effects of androgens on behavioral and vomeronasal responses to chemosensory cues in male terrestrial salamanders (Plethodon shermani).

Chemosensory stimuli and sex steroid hormones are both required for the full expression of social behaviors in many species. The terrestrial salamander, Plethodon shermani, is an emerging nonmammalian system for investigating the nature and evolution of pheromonal communication, yet little is known regarding the role of sex steroid hormones. We hypothesized that increased circulating androgen levels in male P. shermani enhance chemoreception through morphological, behavioral, and physiological mechanisms. Experimental elevation of plasma androgens increased development of cirri, morphological structures thought to enhance the transfer of chemosensory cues from the substrate to the vomeronasal organ (VNO). Elevated plasma androgens also increased expression of a chemo-investigatory behavior (nose tapping) and increased preference for some female-derived chemosensory cues. Male-produced courtship pheromones activated a large number of cells in the VNO as measured by the method of agmatine uptake. However, androgen levels did not affect the total number of vomeronasal cells activated by male-produced courtship pheromones. Future studies will determine whether androgens potentially modulate responsiveness of the VNO to female-derived (as opposed to male-derived) chemosensory cues.

Analysis of Variance↗

PubMed2006

Male pheromone protein components activate female vomeronasal neurons in the salamander Plethodon shermani.

BACKGROUND: The mental gland pheromone of male Plethodon salamanders contains two main protein components: a 22 kDa protein named Plethodon Receptivity Factor (PRF) and a 7 kDa protein named Plethodon Modulating Factor (PMF), respectively. Each protein component individually has opposing effects on female courtship behavior, with PRF shortening and PMF lengthening courtship. In this study, we test the hypothesis that PRF or PMF individually activate vomeronasal neurons. The agmatine-uptake technique was used to visualize chemosensory neurons that were activated by each protein component individually. RESULTS: Vomeronasal neurons exposed to agmatine in saline did not demonstrate significant labeling. However, a population of vomeronasal neurons was labeled following exposure to either PRF or PMF. When expressed as a percent of control level labeled cells, PRF labeled more neurons than did PMF. These percentages for PRF and PMF, added together, parallel the percentage of labeled vomeronasal neurons when females are exposed to the whole pheromone. CONCLUSION: This study suggests that two specific populations of female vomeronasal neurons are responsible for responding to each of the two components of the male pheromone mixture. These two neural populations, therefore, could express different receptors which, in turn, transmit different information to the brain, thus accounting for the different female behavior elicited by each pheromone component.

Animals↗

PubMed2005

Lineage-specific differences in evolutionary mode in a salamander courtship pheromone.

Functionally equivalent genes may evolve heterogeneously across closely related taxa as a consequence of lineage-specific selective pressures. Such disparate evolutionary modes are especially prevalent in genes that encode postcopulatory reproductive proteins, presumably as a result of sexual selection. We might therefore expect genes that mediate reproduction prior to insemination to evolve in a similar manner. Plethodontid receptivity factor (PRF), a proteinaceous salamander pheromone produced by the male, increases female receptivity during courtship interactions. To test for lineage-specific differences in PRF's evolution, we intensively sampled PRF genes across the eastern Plethodon phylogeny (27 spp.; 34 populations) to compare gene diversification, rates of evolution, modes of selection, and types of amino acid substitution. Our analyses indicate that PRF evolutionary dynamics vary considerably from lineage to lineage. Underlying this heterogeneity, however, are two well-defined transitions in evolutionary mode. The first mode is representative of a typical protein profile, wherein neutral divergence and purifying selection are the dominant features. The second mode is characterized by incessant, cyclical evolution driven by positive selection. In this mode, the positively selected sites are bound by a limited assortment of acceptable amino acids that appear to evolve independently of other sites, resulting in a tremendous number of unique PRF alleles. Several of these selected sites are implicated in receptor binding. These sites are apparently involved in a molecular tango in which the male signal and female receptors coevolve within a confined molecular space. PRF's lineage-specific evolutionary dynamics, in combination with evidence of a molecular tango, highlight the molecular action of sexual selection on a chemical signal that is used during courtship.

Amino Acid Sequence↗

PubMed2004

Stabilizing selection on behavior and morphology masks positive selection on the signal in a salamander pheromone signaling complex.

Natural selection maintains the integration and coordination of sets of phenotypic characters that collectively perform a task. In functional complexes in which characters span molecular to behavioral levels of organization, we might then expect similar modes of selection to produce similar patterns in evolutionary divergence at each level. To test this expectation, we diagnosed selection at behavioral, morphological, and molecular levels for courtship pheromone signaling by plethodontid salamanders. At the levels of morphology and behavior tens of millions of years of stasis (stabilizing selection) occur on each side of a transition from vaccination to olfactory delivery modes. As a proxy for the molecular level, we used plethodontid receptivity factor (PRF), a protein that is an active component of the pheromone. We cloned PRF from 12 Plethodon spp. spanning the delivery transition and obtained multiple alleles from each individual surveyed. Analyses of 61 alleles for PRF identified elevated nonsynonymous over synonymous substitution rates along lineages in a molecular phylogeny, and at 8% of sites in the protein, indicating that positive (directional) selection has acted on this vertebrate pheromone gene. Structural models showed PRF is in a family of cytokines characterized by a four-alpha-helix bundle. Positive selection in PRF was associated with receptor binding sites that are under purifying selection in other cytokines of that family. The evolutionary dynamics of the plethodontid pheromone delivery complex consists of stabilizing selection on morphological and behavioral aspects of signal delivery but positive selection on the signal mediated by receptors. Thus, different selection modes prevail at different levels in this reproductive functional complex. Evolutionary studies of integrated sets of characters therefore require separate analyses of selective action at each level.

Amino Acid Sequence↗

PubMed2002

Pheromonal activation of vomeronasal neurons in plethodontid salamanders.

Pheromones from the mental glands of male plethodontid salamanders increase sexual receptivity in conspecific females. The pheromone enters the vomeronasal organ during courtship to produce this effect. Vomeronasal neurons from female Plethodon shermani were examined following exposure to male pheromone or saline placed on the nares. Agmatine was used in conjunction with the pheromone to enable immunocytochemical visualization of chemosensory neurons that were activated by the pheromone. Olfactory neurons exposed to pheromone or saline, and vomeronasal neurons exposed to saline did not demonstrate significant labeling. A population of vomeronasal neurons was intensely labeled following exposure to the pheromone. This study suggests that a specific population of vomeronasal neurons in a female plethodontid salamander is responsible for transmitting pheromonal information to the brain to produce modifications in behavior.

Animals↗