Quantifying the Binding and Target-Search Kinetics of Transcriptional Regulatory Factors by Live-Cell Single-Molecule Tracking.

Eukaryotic transcriptional regulatory factors, such as transcription factors and epigenetic regulatory factors, must locate, bind, and assemble at specific genomic regions to execute functions within the complex and crowded environment of the nucleus. These dynamic processes are typically at nonequilibrium, so quantifying their binding and target-search processes within the native environment is essential for understanding transcriptional mechanisms. Live-cell single-molecule tracking (SMT) is an emerging technique that can be utilized to observe molecular trajectories of individual transcriptional regulatory complexes within the nucleus. Here, we describe the use of live-cell SMT to observe trajectories of individual transcriptional regulatory complexes. We delineate the imaging analysis to obtain chromatin-bound fraction and residence time. Finally, we elaborate on the kinetic modeling to estimate target-search parameters. These binding and target-search parameters facilitate the understanding of how transcription is spatially and temporally regulated under physiological and pathological conditions.

High-risk HPV testing improves accuracy in detection of CIN2+ lesions in ASC-H postmenopausal women? An academic hospital experiences.

Reflex human papilloma virus (HPV) testing with "atypical squamous cells, cannot exclude high-grade squamous lesion (ASC-H)" cytologic diagnosis is not recommended by American Society for Colposcopy and Cervical Pathology guidelines. Studies have shown human papillomavirus (HPV)-negative ASC-H patients of increased age are low risk for cervical intraepithelial neoplasia 2 or worse (CIN2+) lesions on colposcopic follow-up. We retrospectively assessed the efficacy of reflex HPV testing in postmenopausal women with ASC-H in the Los Angeles County hospitals and clinics in a 5-year period. Of a total 85 clinically postmenopausal women with ASC-H, 31 (36.5%) women were found to have CIN2+ lesions on follow-up biopsy and five of them were HPV-negative. Of the women with CIN2+ lesions and positive HPV, 13 (41.9%) were high-risk HPV (hrHPV) 16/18/45 positive and 13 (41.9%) were hrHPV-other subtype positive. Women with positive HPV had an over 3-fold increased risk of developing CIN2+ lesions (P = 0.008). Relative risk of hrHPV16/18/45 was 1.79-fold higher than that of hrHPV-other subtype. The positive predictive value and negative predictive value of hrHPV were 49.1% and 84.4%, respectively. CIN2+ detection rate in Hispanic women with positive hrHPV was higher than in non-Hispanic women (53.8% versus 35.7%). Overall, postmenopausal women with ASC-H cytology result and negative hrHPV were less likely to develop CIN2+ lesions, whereas about half of ASC-H postmenopausal women develop CIN2+ lesions if hrHPV positive, especially if hrHPV 16/18/45 positive. Therefore, triaging ASC-H postmenopausal women with cotesting or, ideally, hrHPV genotyping should be considered as optimal clinical practice to avoid overtreatment.

Expression of high molecular weight cytokeratin-A novel feature of aggressive and innate hormone-refractory prostatic adenocarcinoma.

BACKGROUND: Castration-resistance is common in advanced prostatic adenocarcinomas (PACs) treated with androgen deprivation therapy (ADT) and usually occurs after 2 years following treatment. A minority of PACs confer innate ADT resistance without prior hormonal treatment. The expression of HMWCK in PAC cells has not been studied. This study aimed to investigate the clinicopathologic and genomic features of HMWCK-expressing PACs and the relationship to ADT resistance. METHODS: A total of 469 PACs were studied for HMWCK expression (39 postradiotherapy, 57 post-ADT, 373 treatment-naïve PACs). Clinicopathologic correlations of the HMWCK expression with tumor grade groups, specific tumor morphologies, tumor stages and disease recurrence/persistence/progression were performed. Five HMWCK+ PACs were also sequenced for genetic alterations. RESULTS: Thirty one of the 469 cases (6.6%) showed variable HMWCK+ PAC. The HMWCK+ PAC often focally presented in the tumor and vast majority were associated with high Gleason scores and unfavorable growth patterns (cribriform, comedo-necrosis, and intraductal carcinoma) as well as high tumor stages. A small percentage of the HMWCK+ PCA (2/31, 6.5%) presented with frank squamous histomorphology. Vast majority (22/31, 87%) had no history of prior ADT. The HMWCK+ PAC all displayed diminished to lost expression of AR/NKX3.1. Most of the cases progressed within 12 months of ADT or disease persisted despite ADT. Of the 5 HMWCK+ PACs subjected to gene sequencing, 4 presented with PTEN/PI3K/MAPK pathway alterations. CONCLUSION: The study demonstrated HMWCK+ PAC to be a novel type of innate ADT-resistant PAC. Overexpression of HMWCK in PAC can be potentially used as a surrogate biomarker for aggressive and innate hormone-refractory PACs. The genetic alterations imply potential therapeutic implications of PI3K/MAPK inhibitors in the treatment of these deadly diseases.

Tumor lysis syndrome following ifosfamide monotherapy in metastatic osteosarcoma: a case report and review of the literature.

BACKGROUND: Tumor lysis syndrome is an oncologic emergency that involves multiple metabolic abnormalities and clinical symptoms such as acute renal failure, cardiac arrhythmias, seizures, and multiorgan failure, and may be fatal if not promptly recognized. Tumor lysis syndrome occurs most often in patients with hematologic malignancies, and relatively few cases have been described in patients with sarcoma. CASE PRESENTATION: A 64-year-old male of Asian heritage presented to his primary care physician with a right lower-extremity mass and was ultimately diagnosed with widely metastatic osteosarcoma. He was treated with one cycle of cisplatin and doxorubicin that was complicated by hypervolemia and hypoxic respiratory failure. Given concerns for volume overload, therapy was changed to single-agent, dose-reduced ifosfamide. After receiving one dose of ifosfamide 1 g/m2 (1.8 g total) intravenously over 1 hour, the patient developed renal failure, hyperuricemia, hyperkalemia, hyperphosphatemia, and lactic acidosis. The patient ultimately died from severe electrolyte abnormalities associated with tumor lysis syndrome. CONCLUSION: This is the first instance of tumor lysis syndrome described in a patient with osteosarcoma undergoing ifosfamide monotherapy. Clinicians must be vigilant in identifying tumor lysis syndrome regardless of the malignancy type or chemotherapy regimen in order to prevent potentially fatal complications.

A multidisciplinary team-based approach with lifestyle modification and symptom management to address the impact of androgen deprivation therapy in prostate cancer: A randomized phase II study.

BACKGROUND: Androgen deprivation therapy (ADT) is associated with numerous toxicities that are potentially modifiable. We sought to evaluate the impact of participation in a multidisciplinary clinic, STAND (Supportive Therapy in Androgen Deprivation) Clinic, designed to provide individualized lifestyle modification and management of ADT-related side effects. METHODS: This phase II study recruited men with prostate cancer who had started ADT <6 months prior to enrollment, and in whom ADT was planned for at least 12 months following enrollment. Patients were randomized in a 1:1 ratio to either the STAND Clinic or usual care. Patients randomized to the STAND Clinic were provided monthly multidisciplinary assessment and counseling on exercise, nutrition, and symptom management for 12 months on a rotating schedule. Primary outcome was change from baseline to 12 months in percent body fat. Feasibility outcomes were also assessed by measuring percentage of completed visits. Secondary outcomes included change from baseline to 12 months in 3 domains: (1) metabolic impact and bone health, (2) quality of life (QOL), and (3) physical activity. RESULTS: A total of 25 men were randomized to STAND clinic, and 23 were randomized to usual care. The study did not meet its accrual target of 32 men in each arm and was closed early due to lack of financial support. Overall, 91% (295 of 325) of STAND clinic visits were completed. Eighteen out of the 25 patients in STAND clinic arm (72%) completed all 12 months of STAND clinic visits, and 80% (20 of 25) completed the first 6 months. For all primary and secondary outcomes, there were no statistically significant differences between treatment arms. CONCLUSION: Individualized and comprehensive management of ADT toxicities in a multidisciplinary clinic was well attended by patients. However, we did not find any differences in the outcomes assessed between the intervention arm and control.

Transparent Platinum Counter Electrode Prepared by Polyol Reduction for Bifacial, Dye-Sensitized Solar Cells.

Pt catalytic nanoparticles on F-doped SnO2/glass substrates were prepared by polyol reduction below 200 °C. The polyol reduction resulted in better transparency of the counter electrode and high power-conversion efficiency (PCE) of the resultant dye-sensitized solar cells (DSSCs) compared to conventional thermal reduction. The PCEs of the DSSCs with 5 µm-thick TiO2 photoanodes were 6.55% and 5.01% under front and back illumination conditions, respectively. The back/front efficiency ratio is very promising for efficient bifacial DSSCs.

From individual movement behaviour to landscape-scale invasion dynamics and management: a case study of lionfish metapopulations.

Modelling the dynamics of small, interconnected populations, or metapopulations, can help pinpoint habitat patches that are critical for population persistence in patchy habitats. For conservation purposes, these patches are typically earmarked for protection, but for invasive species management, these patches could be targeted to hasten the populations' demise. Here, we show how metapopulation modelling, coupled with an understanding of size-dependent dispersal behaviour, can be used to help optimize the distribution of limited resources for culling specific populations of invasive Indo-Pacific lionfish (Pterois volitans) in the western Atlantic. Through simulation using fitted model parameters, we derive three insights that can inform management. First, culling lionfish from target patches reduces the probability of lionfish occupancy at surrounding patches. Second, this effect depends on patch size and connectivity, but is strongest at the local scale and decays with distance. Finally, size-dependent dispersal in lionfish means that size-selective culling can change both a population's size distribution and dispersal potential, with cascading effects on network connectivity, population dynamics and management outcomes. By explicitly considering seascape structure and movement behaviour when allocating effort to the management of invasive species, managers can optimize resource use to improve management outcomes. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.

Nuclear condensates of the Polycomb protein chromobox 2 (CBX2) assemble through phase separation.

Polycomb group (PcG) proteins repress master regulators of development and differentiation through organization of chromatin structure. Mutation and dysregulation of PcG genes cause developmental defects and cancer. PcG proteins form condensates in the cell nucleus, and these condensates are the physical sites of PcG-targeted gene silencing via formation of facultative heterochromatin. However, the physiochemical principles underlying the formation of PcG condensates remain unknown, and their determination could shed light on how these condensates compact chromatin. Using fluorescence live-cell imaging, we observed that the Polycomb repressive complex 1 (PRC1) protein chromobox 2 (CBX2), a member of the CBX protein family, undergoes phase separation to form condensates and that the CBX2 condensates exhibit liquid-like properties. Using site-directed mutagenesis, we demonstrated that the conserved residues of CBX2 within the intrinsically disordered region (IDR), which is the region for compaction of chromatin in vitro, promote the condensate formation both in vitro and in vivo We showed that the CBX2 condensates concentrate DNA and nucleosomes. Using genetic engineering, we report that trimethylation of Lys-27 at histone H3 (H3K27me3), a marker of heterochromatin formation produced by PRC2, had minimal effects on the CBX2 condensate formation. We further demonstrated that the CBX2 condensate formation does not require CBX2-PRC1 subunits; however, the condensate formation of CBX2-PRC1 subunits depends on CBX2, suggesting a mechanism underlying the assembly of CBX2-PRC1 condensates. In summary, our results reveal that PcG condensates assemble through liquid-liquid phase separation (LLPS) and suggest that phase-separated condensates can organize PcG-bound chromatin.

The use of botanical products and vitamins in sunscreens.

The use of botanical products and vitamins in skin care creams and sunscreens is prevalent. Herein we conduct an evaluation of sunscreens to quantitatively assess how often sunscreens incorporate botanically derived products and vitamins. The most commonly used botanicals products and vitamins are identified and stratified based on the sunscreen sun protection factor (SPF). The overall prevalence for the use of botanical agents and vitamins was 62% and 79%, respectively. Aloe vera and licorice root extracts were the most common botanical agents used in sunscreens. Retinyl palmitate was the most common vitamin derivative utilized in sunscreens. The prices of sunscreens significantly increased when more than one botanical product was added. Botanical products and vitamins are widely utilized in sunscreens and more research is needed to assess how their inclusion may enhance or alter the function of sunscreens.

The economic burden of sunscreen usage.

Excessive sun exposure is known to be the leading cause of skin cancer. The direct cellular damage inflicted by the ultraviolet (UV) radiation from the sun results in premature aging, DNA damage, and mutations that ultimately lead to skin cancer. Sunscreens are highly recommended to protect against UV radiation. However, little research has been conducted on the economic burden of sunscreen use. In this study, we aimed to evaluate the annual cost of sunscreen under both ideal and actual use conditions while stratifying for the sun protection factor (SPF) and by the name brand or equivalent store brand sunscreen. Pricing data was collected for sunscreens of SPF 30, 50, 70, and 100. For each type of sunscreen, the size and price of the container were recorded. Our results demonstrated that sunscreen prices increased with SPF but purchasing a generic sunscreen resulted in savings of 40%-50%. Our estimates reveal that sunscreens are affordable with annual expenditures ranging from $30.21 to $61.94, depending on brand, for SPF 50 sunscreens used with minimal application density for the average person.

The activating Ly49W and inhibitory Ly49G NK cell receptors display similar affinities for identical MHC class I ligands.

The Ly49 receptor family plays an important role in the regulation of murine natural killer (NK) cell effector function. They recognize cell surface-expressed class I MHC (MHC-I) and are functionally equivalent to the killer Ig-related receptors (KIRs) in human NK cells. Ly49s exist in activating and inhibitory forms with highly homologous extracellular domains, displaying greater variability in the stalk regions. Inhibitory Ly49s can recognize self-MHC-I and therefore mediate tolerance to self. The role of activating Ly49 receptors is less clear. Some activating Ly49 receptors have been shown to recognize MHC-I molecules. The binding affinity of activating Ly49 receptors with MHC-I is currently unknown, and we sought to examine the affinities of two highly related receptors, an activating and an inhibitory Ly49 receptor, for their shared MHC-I ligands. The ectodomain of inhibitory Ly49G of the BALB/c mouse strain is highly similar to the Ly49W activating receptor in the nonobese diabetic (NOD) mouse. Recombinant soluble Ly49G and W were expressed, refolded, and analyzed for binding affinity with MHC-I by surface plasmon resonance. We found that Ly49G and Ly49W bound with similar affinity to the same MHC-I molecules. These results are a first determination of an activating Ly49 receptor affinity for MHC-I and show that, unlike prior results obtained with activating and inhibitory KIR receptors, functional homologues to Ly49 receptors, activating and inhibitory Ly49, can recognize common MHC-I ligands, with similar affinities.

On the evolution of omnivory in a community context.

Omnivory is extremely common in animals, yet theory predicts that when given a choice of resources specialization should be favored over being generalist. The evolution of a feeding phenotype involves complex interactions with many factors other than resource choice alone, including environmental heterogeneity, resource quality, availability, and interactions with other organisms. We applied an evolutionary simulation model to examine how ecological conditions shape evolution of feeding phenotypes (e.g., omnivory), by varying the quality and availability (absolute and relative) of plant and animal (prey) resources. Resulting feeding phenotypes were defined by the relative contribution of plants and prey to diets of individuals. We characterized organisms using seven traits that were allowed to evolve freely in different simulated environments, and we asked which traits are important for different feeding phenotypes to evolve among interacting organisms. Carnivores, herbivores, and omnivores all coexisted without any requirement in the model for a synergistic effect of eating plant and animal prey. Omnivores were most prevalent when ratio of plants and animal prey was low, and to a lesser degree, when habitat productivity was high. A key result of the model is that omnivores evolved through many different combinations of trait values and environmental contexts. Specific combinations of traits tended to form emergent trait complexes, and under certain environmental conditions, are expressed as omnivorous feeding phenotypes. The results indicate that relative availabilities of plants and prey (over the quality of resources) determine an individual's feeding class and that feeding phenotypes are often the product of convergent evolution of emergent trait complexes under specific environmental conditions. Foraging outcomes appear to be consequences of degree and type of phenotypic specialization for plant and animal prey, navigation and exploitation of the habitat, reproduction, and interactions with other individuals in a heterogeneous environment. Omnivory should not be treated as a fixed strategy, but instead a pattern of phenotypic expression, emerging from diverse genetic sources and coevolving across a range of ecological contexts.

Tuning primary metabolism for heterologous pathway productivity.

Tuning expression of competing endogenous pathways has been identified as an effective strategy in the optimization of heterologous production pathways. However, intervention at the first step of glycolysis, where no alternate routes of carbon utilization exist, remains unexplored. In this work we have engineered a viable E. coli host that decouples glucose transport and phosphorylation, enabling independent control of glucose flux to a heterologous pathway of interest through glucokinase (glk) expression. Using community sourced and curated promoters, glk expression was varied over a 3-fold range while maintaining cellular viability. The effects of glk expression on the productivity of a model glucose-consuming pathway were also studied. Through control of glycolytic flux we were able to explore a number of cellular phenotypes and vary the yield of our model pathway by up to 2-fold in a controllable manner.

Phytochemicals and Naturally Derived Substances for Wound Healing.

BACKGROUND: Complementary and alternative medicines (CAMs) are widely used by the general public. Natural products including plant-derived extracts (phytochemicals) and naturally derived substances, such as honey, are an important component of CAM. Here, we review the evidence for their use in wound care. THE PROBLEM: Wound healing is complex and disruption of this process can lead to considerable morbidity, including chronic wounds, infection, and scarring. Natural products have a long history of use in wound care, but there are only a few rigorous studies. With the growing interest in the use of natural products and the belief that they are safer than standard therapies, it is vital to understand the current knowledge of their efficacy and side effects. BASIC/CLINICAL SCIENCE ADVANCES: Natural products possess antioxidant, anti-inflammatory, angiogenic, and cell synthesis-modulating components among many others. However, this complex composition of chemicals may increase the risk for irritant or allergic side effects. CLINICAL CARE RELEVANCE: Natural products can be much cheaper than conventional treatments, but further study is needed to better understand their efficacy. The type of wound and the potential for side effects need to be carefully considered when choosing a treatment. CONCLUSION: The research to date is supportive of the use of natural products in wound care. Patients need to be cautioned of potential side effects. Collaborative research between allopathic medicine and medical systems that frequently employ phytochemicals and naturally derived substances, such as Ayurveda and naturopathy, will provide a better understanding of how to integrate natural products into wound care.

Recognition of class I MHC by a rat Ly49 NK cell receptor is dependent on the identity of the P2 anchor amino acid of bound peptide.

Members of the rodent Ly49 receptor family control NK cell responsiveness and demonstrate allele specificity for MHC class I (MHC-I) ligands. For example, the rat Ly49i2 inhibitory NK cell receptor binds RT1-A1(c) but not other rat MHC class Ia or Ib molecules. RT1-A1(c) preferentially binds peptides with proline at the second, or P2, position, which defines it as an HLA-B7 supertype MHC-I molecule. Previously, our laboratory showed that mutations within the MHC-I supertype-defining B-pocket of RT1-A1(c) could lead to alterations in P2 anchor residues of the peptide repertoire bound by RT1-A1(c) and loss of recognition by Ly49i2. Although suggestive of peptide involvement, it was unclear whether the peptide P2 anchor residue or alteration of the RT1-A1(c) primary sequence influenced Ly49i2 recognition. Therefore, we directly investigated the role of the P2 anchor residue of RT1-A1(c)-bound peptides in Ly49i2 recognition. First, fluorescent multimers generated by refolding soluble recombinant RT1-A1(c) with individual synthetic peptides differing only at the P2 anchor residue were examined for binding to Ly49i2 NK cell transfectants. Second, cytotoxicity by Ly49i2-expressing NK cells toward RMA-S target cells expressing RT1-A1(c) bound with peptides that only differ at the P2 anchor residue was evaluated. Our results demonstrate that Ly49i2 recognizes RT1-A1(c) bound with peptides that have Pro or Val at P2, whereas little or no recognition is observed when RT1-A1(c) is complexed with peptide bearing Gln at P2. Thus, the identity of the P2 peptide anchor residue is an integral component of MHC-I recognition by Ly49i2.

Size-mediated adaptive foraging: a host-selection strategy for insect parasitoids.

Foraging models are useful tools for generating predictions on predator-prey interactions, such as habitat or diet choice. However, the majority of studies attempting to explain adaptive behaviour using optimality criteria have assumed that there is no trait (e.g. size) variation among individual consumers or their prey. Hymenopteran parasitoids that attack the free-living stages of their host are an ideal system for studying the influence of body size on host selection because of the wide range of adult parasitoid sizes coupled with the defensive capabilities of their hosts. We report here our application of an experimentally parameterized host selection model to investigate the influence of parasitoid body size on the range of acceptable host instar classes. Using a demographic model, we compared the efficiency of parasitoids using an optimal host selection strategy against parasitoids using an indiscriminate host selection strategy over a range of different parasitoid body sizes. Net fitness accrual of parasitoids and the impact of host instar selection on aphid recruitment were assessed on different stage-structured aphid populations. Our results demonstrate that optimal host selection allows larger parasitoids to utilize a wider range of hosts. However, smaller parasitoids receive the greatest benefits from selecting hosts optimally by utilizing a restricted range of small, poorly defended hosts when they are abundant. We argue that the correlation between flexible host selection behaviour and adult body size may be a general phenomenon that applies to the majority of hymenopteran parasitoids that attack free-living, well-defended hosts. The potential of within-generation behavioural interactions to impact between-generation dynamics in host-parasitoid populations are discussed.

The rat RT1-A1c MHC molecule is a xenogeneic ligand recognized by the mouse activating Ly-49W and inhibitory Ly-49G receptors.

Mouse Ly-49 receptors are known to recognize xenogeneic ligands from hamster and rat. However, until now, there has been no description of a specific rat xenogeneic ligand for any mouse Ly-49 receptor. In this report, we identify RT1-A1c, a rat classical class I MHC molecule, as a ligand for the Ly-49G(BALB/c) inhibitory receptor and the closely related activating receptor, Ly-49W. Xenogeneic class I recognition of targets from PVG but not DA strain rats was mapped to the classical region of the RT1c haplotype by using Con A blasts from RT1c/RT1av1 intra-MHC recombinant rats as targets for RNK-16 cells expressing either Ly-49W or Ly-49G(BALB/c) receptors. Individual expression of class I molecules from PVG and DA rat strains in YB2/0 target cells demonstrate the xenogeneic recognition to be allele specific, because other class I molecules of the RT1c haplotype, RT1-A2c and RT1-U2c, and a classical class I molecule encoded by the RT1av1 haplotype, RT1-Aa, are not recognized by Ly-49W and -G(BALB/c). Furthermore, specificity for RT1-Ac can be transferred from Ly-49W to Ly-49P, which is normally unable to recognize RT1-Ac, by substitution of three residues shared by Ly-49W and -G(BALB/c) but not Ly-49P. These residues are located in the Ly-49 beta4-beta5 loop, which can determine class I allele specificity in mouse Ly-49 receptor interactions with mouse class I ligands, suggesting that mouse Ly-49 recognition of rat class I molecules follows similar principles of interaction. These findings have implications for xenotransplantation studies and for discerning Ly-49 recognition motifs present in MHC molecules.

Ly-49 receptors and their functions.

Ly-49 receptors are lectin-like type II transmembrane disulfide-bonded homodimers expressed on natural killer (NK) cells and some T-cell subsets. Cell-mediated cytotoxicity and release of cytokines/chemokines are functions regulated by Ly-49 recognition of class I major histocompatibility complex proteins (MHC-I) or virus-encoded MHC-like product(s). Here we examine diversity and conservation found within the Ly-49 gene family and explore the importance of polymorphism in Ly-49 receptor expression, specificity, and function. Several parallels are evident between Ly-49 receptors in rodents and killer Ig-related (KIR) receptors in humans, including receptor gene amplification and diversification, expression patterns, MHC-I specificity, shared signaling, and ultimate effects on NK-cell functions. These similarities suggest that insights gained in defining Ly-49 receptor functions in small animal models could have direct relevance to existing clinical challenges where there may be opportunities to manipulate human NK cells and KIR receptors for therapeutic benefit.

Dynamic versus instantaneous models of diet choice.

We investigate the dynamics of a series of two-prey-one-predator models in which the predator exhibits adaptive diet choice based on the different energy contents and/or handling times of the two prey species. The predator is efficient at exploiting its prey and has a saturating functional response; these two features combine to produce sustained population cycles over a wide range of parameter values. Two types of models of behavioral change are compared. In one class of models ("instantaneous choice"), the probability of acceptance of the poorer prey by the predator instantaneously approximates the optimal choice, given current prey densities. In the second class of models ("dynamic choice"), the probability of acceptance of the poorer prey is a dynamic variable, which begins to change in an adaptive direction when prey densities change but which requires a finite amount of time to approach the new optimal behavior. The two types of models frequently predict qualitatively different population dynamics of the three-species system, with chaotic dynamics and complex cycles being a common outcome only in the dynamic choice models. In dynamic choice models, factors that reduce the rate of behavioral change when the probability of accepting the poorer prey approaches extreme values often produce complex population dynamics. Instantaneous and dynamic models often predict different average population densities and different indirect interactions between prey species. Alternative dynamic models of behavior are analyzed and suggest, first, that instantaneous choice models may be good approximations in some circumstances and, second, that different types of dynamic choice models often lead to significantly different population dynamics. The results suggest possible behavioral mechanisms leading to complex population dynamics and highlight the need for more empirical study of the dynamics of behavioral change.

Reciprocal transfer of class I MHC allele specificity between activating Ly-49P and Ly-49W receptors by exchange of beta 4-beta 5 loop residues.

Receptors of the Ly-49 multigene family regulate rodent NK cell functions. Ly-49Rs are highly polymorphic and exist in either activating or inhibitory forms. Examples of both Ly-49 receptor types have been shown to recognize class I MHC ligands. Ly-49Rs can distinguish between class I alleles, but the molecular basis of this discrimination is unknown. Two activating receptors, Ly-49P and Ly-49W, differ in class I recognition, recognizing H-2D(d), or H-2D(d) and D(k), respectively. In this report, we demonstrate that specificity for H-2D(k) can be transferred from Ly-49W to Ly-49P by substituting 3 aa predicted to reside in the beta4-beta5 loop of Ly-49W into Ly-49P. Replacement of these same residues of Ly-49W with corresponding residues in Ly-49P eliminates H-2D(k) recognition while still preserving H-2D(d) recognition. Further mutagenesis indicates that all 3 aa facilitate optimal class I specificity exchange. These results provide the first evidence for a specific site on Ly-49Rs, the beta4-beta5 loop, in determining class I MHC allele specificity.