LRIT1 Modulates Adaptive Changes in Synaptic Communication of Cone Photoreceptors

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Kinetics of 125I-PDGF binding and down-regulation of PDGF receptor in human arterial smooth muscle cell strains during cellular senescence in vitro

Platelet-derived growth factor (PDGF) is one of the major mitogens in serum to stimulate replication of human smooth muscle cells (SMCs) in culture. Previous studies using human fibroblasts failed to demonstrate changes in the receptor systems for growth factors during cellular senescence. We investigated the kinetics of ¹²⁵I-PDGF(-BB) binding and down-regulation of the PDGF receptor in three human arterial SMC strains during cellular aging. The number of specific ¹²⁵I-PDGF binding sites per cell increased slightly at a population doubling level (PDL) of 60%–80% of life span and then decreased at the PDL above 90%. The number of receptors per cell-surface area decreased with increasing in vitro age. The apparent Kd for the ¹²⁵I-PDGF binding decreased with in vitro senescence. The internalization and degradation of ¹²⁵I-PDGF per receptor were significantly reduced in senescent SMCs than young cells. Furthermore, down-regulation of the PDGF receptor was significantly greater in sensescent SMCs than young cells. Immunoblot studies demonstrated that changes in b?-subunit of the PDGF receptor accounted for those in the studies using ¹²⁵I-PDGF and that tyrosine phosphorylation of the PDGF receptor was significantly greater in young SMCs than aged cells. Our results suggest that age-related changes in the receptor systems for PDGF may be important contributors to the failure of DNA synthesis in senescent SMCs. © 1995 Wiley-Liss, Inc.     

Reduced antennal sensitivity, behavioural response, and attraction of male codling moths, Cydia pomonella, to their pheromone (E,E)-8,10-dodecadien-1-ol following various pre-exposure regimes

The effects of pre‐exposing male codling moths, Cydia pomonella (L.) (Lepidoptera: Tortricidae), to their pheromone (E,E)‐8,10‐dodecadien‐1‐ol (codlemone), in static and moving air, under laboratory and field conditions, on subsequent antennal sensitivity, behavioural responsiveness, and attraction to codlemone were investigated. In flight tunnel experiments, the percentage of moths wing fanning and taking flight were mostly unaffected, but upwind flight to, and contact with, pheromone sources known to elicit responses of both were shown to depend on the intensity and duration of previous exposure to codlemone and recovery time between exposure and assessment. Ten to 30‐min pre‐exposures to codlemone in static air (≈ 35 µg l^?1) not only caused a 99% reduction in attraction, but also significantly reduced electroantennogram response to codlemone. Recovery of full antennal sensitivity to codlemone took more than 1 h, but recovery of attraction took over 4 h, suggesting that habituation is also partially involved in reduced behavioural responsiveness following pre‐exposure. Seventy‐five min exposures to codlemone in moving air (5–10 cm s^?1) at rates of 0.9, 4.5, and 18 µg h^?1 from Celcon fibres caused 75, 86, and 99% disruption, respectively. However, 30–34‐h exposure of caged moths to air moving through an orchard treated with 1000 Isomate‐C® dispensers ha^?1 releasing approximately 20 µg h^?1 per dispenser during tests, had no impact on moth response in flight‐tunnel assays 30 min after removal from the orchard. In this treated orchard, catches of free‐flying moths in pheromone‐baited traps were completely inhibited. If observed mechanisms such as long‐lasting antennal adaptation or habituation of the central nervous system contribute to the disruption of pheromone communication among codling moths under field conditions, it seems unlikely that they occur following exposure to the average atmospheric concentrations of codlemone. For these effects to be important, codling moths may require close contact with pheromone sources for extended periods, or repeated close encounters.     

Purification and Characteristics of Membrane-Bound Chitinase of Anaerobic Ruminal Fungus Piromyces communis OTS1

A membrane-bound chitinase from cell wall fractions of the anaerobic ruminal fungus, Piromyces communis OTS1, was purified by affinity chromatography, gel filtration, and chromatofocusing. The molecular size of the chitinase was estimated by gel filtration to be 42.4 kDa and by SDS-PAGE to be 44.8 kDa, and its pI was 4.4. Activity was inhibited by Hg²⁺ and allosamidin. The activity at 39°C was greatest at pH 6.0. It had an ‘endo’ type action. Solubilization tests indicated that plasmalemma-bound chitinase was held in place by an electrostatic type interaction. Characterization of the membrane-bound chitinase was more similar to that of extracellular chitinase than cytosolic chitinase. This suggested that membrane-bound chitinase was the origin of extracellular chitinase. Received: 15 October 1997 / Accepted: 13 January 1998     

Frequency–dependent pollinator foraging in polymorphic Clarkia xantiana ssp. xantiana populations: implications for flower colour evolution and pollinator interactions

Under many circumstances pollinators are expected to practice positive frequency–dependent foraging in colour-polymorphic plant populations. Theory suggests, however, that competition for floral resources might favor negative frequency–dependent foraging by some pollinator species, possibly contributing to the maintenance of flower colour variation by negative frequency–dependent selection. We addressed this idea with pollination studies of the California annual plant Clarkia xantiana ssp. xantiana (Onagraceae), which is polymorphic for the presence of conspicuous petal spots and is pollinated by several specialist bee species. At the level of entire pollinator assemblages, we did not detect significant fixed flower colour preferences or frequency–dependent foraging. Three species of specialist bee pollinators, however, showed contrasting forms of frequency–dependent foraging. The most widespread species, Hesperapis regularis (Melittidae) exhibited positive frequency dependence. Two other common species, Lasiglossum pullilabre (Halictidae) and Ceratina sequoiae (Apidae), preferred to visit whichever morph (unspotted or spotted) was locally in the minority. All three species were found to be effective at transferring C. xantiana pollen; H. regularis appeared most effective. Our findings suggest that a mixture of positive and negative frequency–dependent selection on flower colour occurs in C. xantiana , with the form and intensity of selection varying in space and time with pollinator assemblages. Negative frequency–dependent selection via pollination dynamics may play a larger role in maintaining genetic variation in flower colour than was previously thought. Our results also suggest an unappreciated form of niche partitioning among specialist pollinators. Genetic polymorphism in flower colour may sometimes facilitate pollinator coexistence.     

Emerging Frontiers in Social Neuroendocrinology and the Study of Nonapeptides

Social neuroendocrinology, which elucidates the physiological mediators of social behavior, has undergone numerous advances since its inception more than 20 yrs ago. Among these was the discovery that the nonapeptides—a family of homologous peptides that includes oxytocin and vasopressin—play a significant role in mediating a variety of affiliative behaviors. However, important gaps remain in our understanding of how the non‐apeptide systems contribute to variations in behavior at several levels, including among species, between the sexes, and within different environmental contexts. This study acknowledges the work and foresight of the late James Goodson by examining emerging trends in social neuroendocrinology.