Two are better than one: Unraveling the functions of cone arrestin in zebrafish (Commentary on Renninger, Gesemann and Neuhauss)

Since the surprising discovery of a second visual arrestin in mammalian pinealocytes and cone photoreceptors, numerous studies have examined cone arrestin's structural and functional similarities to and differences from rod arrestin (Craft et al., 1994; Nikonov et al., 2008). The rod arrestin or Arrestin1 binds to and terminates the light-activated, phosphorylated G-protein-coupled rhodopsin (Xu et al., 1997), whereas both visual arrestins work in concert in cone photoreceptors to shut off the light-activated photoreceptor signal transduction cascade, as shown for mouse Sand M-opsin (Nikonov et al., 2008). In this issue of EJN, Renninger and colleagues add a new dimension to understanding the visual arrestin saga by introducing two rod arrestins (arrS), three b-arrestins, and focusing on two paralogs of cone arrestin (arr3a and arr3b) in the zebrafish (Danio rerio). The Arr3a is exclusively expressed in M- and L-wavelength sensitive cones, whereas Arr3b is found in S- and UV-wavelength-sensitive cones. Their comprehensive study provides the first clear evidence of Arr3a's involvement in the high temporal contrast sensitivity of cone vision. As zebrafish exhibit light responses after 3 days of development, they are an ideal animal to study visual behavior (Brockerhoff et al., 1995). They are tetrachromatic with ultraviolet-sensitive cones as well as red-, green- and blue-sensitive cones, and their retinas continue to grow throughout their life. Using this cone-dominated visual system as a model system for their analysis, Renninger et al. (2011) examined the cellular expression of the distinct isoforms of arrestin in the visual system using a combination of in-situ hybridization and cone arrestin paralog-specific antibodies to examine cellular distribution at different developmental stages. These straightforward morphological experiments were followed by a set of elegant physiological experiments using targeted gene knockdown of the two cone arrestins in zebrafish larvae to unravel their visual responses with electroretinography. The functional knockdown of arr3a led to an electroretinography photo-response recovery delay. Additional experiments with the functional inactivation of arr3a were used to dissect out the psychophysical responses with optokinetics, a stereotypic ocular movement that is probably mediated by the modulation of M- and L-cone input (Orger & Baier, 2005). These latter experiments distinguished behavioral differences between low-contrast (dark-adapted) conditions that affected high temporal frequency patterns, and high-contrast (lightadapted) conditions that showed a deceleration of the temporal transfer function in the arr3a morphant larvae. Because of the lower abundance of the S- and UV-wavelength-sensitive cones in zebrafish, the function of arr3b remains undetermined; however, this work provides conclusive evidence that arr3a regulates high temporal resolution in high acuity color vision with experiments that are not possible in the rod-dominant mammalian retina. This work illustrates the use of the zebrafish as a vertebrate model to address the basic cellular function of cone arrestin and contributes to our broader understanding of visual processing and the complex physiology of high acuity color vision

Retinal Neovascular Disorders: Mouse Models for Drug Development Studies

Neovascularization is a hallmark of several eye diseases leading to visual impairment, and its epidemiological impact is substantial (Lee et al. 1998). In retinal degenerative disease models, neovascularization is the process by which the choroid and/or retina become infiltrated with new blood vessels. In retinal neovascularization (RNV), sprouting retinal vessels penetrate the inner limiting membrane (ILM) and grow into the vitreous, and in some cases, grow through the avascular outer retina into the subretinal space (Campochiaro 2000). Numerous clinical and ­experimental observations indicate that ischemia (or hypoxia) is the driving force behind RNV (Michaelson and Steedman 1949). Occlusion of retinal vessels leading to ischemia is a feature of diseases with RNV, including diabetic retinopathy (DR) and retinopathy of prematurity (ROP) (Campochiaro 2000)

Optimization of Application Timing and Frequency of Microbial Inoculants for Turfgrass Disease Control

NYS IPM Type: Project ReportConsiderable information is now available concerning the use of microbial inoculants for the control of turfgrass diseases. However, despite positive experimental results, few microbial inoculants have been highly effective in field studies or in commercial use on golf courses. A number of studies have shown that microbial agents perform most effectively when populations can be maintained at high levels, usually at populations exceeding 107 cells/g soil. However, applications made during the daytime hours may limit population development due to UV exposure or to desiccation. The limited number of success stories of biological control on golf courses have been from sites where applications of biological control organisms were applied during the overnight hours. Technology is now available for golf course superintendents to culture microbial inoculants on site at the golf course and apply inoculants directly through the irrigation system at any time of the day or night. It is now feasible for superintendents to make applications on a daily basis. This study was designed to evaluate the impacts of application scheduling on the disease control efficacy of introduced microbial inoculants

Photoreceptors of Nrl −/− Mice Coexpress Functional S- and M-cone Opsins Having Distinct Inactivation Mechanisms

The retinas of mice null for the neural retina leucine zipper transcription factor (Nrl −/−) contain no rods but are populated instead with photoreceptors that on ultrastructural, histochemical, and molecular criteria appear cone like. To characterize these photoreceptors functionally, responses of single photoreceptors of Nrl −/− mice were recorded with suction pipettes at 35–37°C and compared with the responses of rods of WT mice. Recordings were made either in the conventional manner, with the outer segment (OS) drawn into the pipette (“OS in”), or in a novel configuration with a portion of the inner segment drawn in (“OS out”). Nrl −/− photoreceptor responses recorded in the OS-out configuration were much faster than those of WT rods: for dim-flash responses tpeak = 91 ms vs. 215 ms; for saturating flashes, dominant recovery time constants, τD = 110 ms vs. 240 ms, respectively. Nrl −/− photoreceptors in the OS-in configuration had reduced amplification, sensitivity, and slowed recovery kinetics, but the recording configuration had no effect on rod response properties, suggesting Nrl −/− outer segments to be more susceptible to damage. Functional coexpression of two cone pigments in a single mammalian photoreceptor was established for the first time; the responses of every Nrl −/− cell were driven by both the short-wave (S, λmax ≈ 360 nm) and the mid-wave (M, λmax ≈ 510 nm) mouse cone pigment; the apparent ratio of coexpressed M-pigment varied from 1:1 to 1:3,000 in a manner reflecting a dorso-ventral retinal position gradient. The role of the G-protein receptor kinase Grk1 in cone pigment inactivation was investigated in recordings from Nrl −/−/Grk1−/− photoreceptors. Dim-flash responses of cells driven by either the S- or the M-cone pigment were slowed 2.8-fold and 7.5-fold, respectively, in the absence of Grk1; the inactivation of the M-pigment response was much more seriously retarded. Thus, Grk1 is essential to normal inactivation of both S- and M-mouse cone opsins, but S-opsin has access to a relatively effective, Grk1-independent inactivation pathway

Vascular contributions to cognitive impairment and dementia including Alzheimer's disease

AbstractScientific evidence continues to demonstrate the linkage of vascular contributions to cognitive impairment and dementia such as Alzheimer's disease. In December, 2013, the Alzheimer's Association, with scientific input from the National Institute of Neurological Disorders and Stroke and the National Heart, Lung and Blood Institute from the National Institutes of Health, convened scientific experts to discuss the research gaps in our understanding of how vascular factors contribute to Alzheimer's disease and related dementia. This manuscript summarizes the meeting and the resultant discussion, including an outline of next steps needed to move this area of research forward

The androgen receptor can signal through Wnt/β-Catenin in prostate cancer cells as an adaptation mechanism to castration levels of androgens

<p>Abstract</p> <p>Background</p> <p>A crucial event in Prostate Cancer progression is the conversion from a hormone-sensitive to a hormone-refractory disease state. Correlating with this transition, androgen receptor (AR) amplification and mutations are often observed in patients failing hormonal ablation therapies. β-Catenin, an essential component of the canonical Wnt signaling pathway, was shown to be a coactivator of the AR signaling in the presence of androgens. However, it is not yet clear what effect the increased levels of the AR could have on the Wnt signaling pathway in these hormone-refractory prostate cells.</p> <p>Results</p> <p>Transient transfections of several human prostate cancer cell lines with the AR and multiple components of the Wnt signaling pathway demonstrate that the AR overexpression can potentiate the transcriptional activities of Wnt/β-Catenin signaling. In addition, the simultaneous activation of the Wnt signaling pathway and overexpression of the AR promote prostate cancer cell growth and transformation at castration levels of androgens. Interestingly, the presence of physiological levels of androgen or other AR agonists inhibits these effects. These observations are consistent with the nuclear co-localization of the AR and β-Catenin shown by immunohistochemistry in human prostate cancer samples. Furthermore, chromatin immunoprecipitation assays showed that Wnt3A can recruit the AR to the promoter regions of Myc and Cyclin D1, which are well-characterized downstream targets of the Wnt signalling pathway. The same assays demonstrated that the AR and β-Catenin can be recruited to the promoter and enhancer regions of a known AR target gene PSA upon Wnt signaling. These results suggest that the AR is promoting Wnt signaling at the chromatin level.</p> <p>Conclusion</p> <p>Our findings suggest that the AR signaling through the Wnt/β-Catenin pathway should be added to the well established functional interactions between both pathways. Moreover, our data show that via this interaction the AR could promote prostate cell malignancy in a ligand-independent manner.</p

Compatibility of Microbial Inoculants with Conventional Turfgrass Pesticides

NYS IPM Type: Project ReportThis project was designed to examine the impact of pesticide applications on the efficacy of commercial microbial inoculants used to suppress turfgrass diseases. Our goal in this research was to document any positive or potentially negative combinations of biological disease control products with commonly-used fungicides, insecticides, and herbicides

Impacts of Conventional Turfgrass Pesticides on the Efficacy of Composted Amendments Used for the Biological Control of Turfgrass Diseases

NYS IPM Type: Project ReportIn the past few years, biological strategies of pest control have been attracting considerable attention among turfgrass scientists as well as golf course superintendents. The approaches are being viewed as an attractive means of reducing the superintendents dependency on chemical pesticides

The Carboxyl Terminal Domain of Phosducin Functions as a Transcriptional Activator

In previous work, we identified a set of phosducin (Phd) isoforms with unknown function including the phosducin (Phd)-like orphan protein 1 (PhLOP1), an amino terminal truncated isoform of the retinal Phd lacking the Gbetagamma binding domain. To investigate the potential biological function of PhLOP1, PhLOP1 was fused at its amino terminus with the DNA binding domain (BD) of the yeast transcriptional factor, GAL4, and used as bait in a yeast two-hybrid screen. Two potential functional protein partners were identified during the screen: SUG1, a subunit of the 26S proteasome and a putative transcriptional mediator, and CRX, a retina- and pineal-specific transcription factor. Upon localizing the interacting domain of PhLOP1 with one of the new partners, SUG1, we found that a domain of 40 amino acids at the carboxyl terminus of Phd and PhLOP1 had intrinsic transcriptional activation activity in yeast. The transactivation activity was further confirmed in mammalian cells. This region contains an acidic domain that has been shown to be involved in the function of several transcriptional activators. In addition, we showed that Phd is cytoplasmic while PhLOP1 is localized predominantly to the nucleus when fused to an enhanced green fluorescent protein (EGFP) and transiently expressed in transfected cells, suggesting that PhLOP1 may play a distinct functional role in transcriptional regulation independent of the known Phd interaction/regulation of Gbetagamma transduction