Yap1 is required for maintenance of adult RPE differentiation.

Nuclear YAP1 plays a critical role in regulation of stem cell proliferation, tissue regeneration, and organ size in many types of epithelia. Due to rapid turnover of most epithelial cell types, the cytoplasmic function of YAP1 in epithelial cells has not been well studied. The retinal pigment epithelium (RPE) is a highly polarized epithelial cell type maintained at a senescence state, and offers an ideal cell model to study the active role of YAP1 in maintenance of the adult epithelial phenotype. Here, we show that the cytoplasmic function of YAP1 is essential to maintain adult RPE differentiation. Knockout of Yap1 in the adult mouse RPE caused cell depolarization and tight junction breakdown, and led to inhibition of RPE65 expression, diminishment of RPE pigments, and retraction of microvilli and basal infoldings. These changes in RPE further prompted the loss of adjacent photoreceptor outer segments and photoreceptor death, which eventually led to decline of visual function in older mice between 6 and 12 months of age. Furthermore, nuclear ß-catenin and its activity were significantly increased in mutant RPE. These results suggest that YAP1 plays an important role in active inhibition of Wnt/ß-catenin signaling, and is essential for downregulation of ß-catenin nuclear activity and prevention of dedifferentiation of adult RPE.

Iodoacetic acid, but not sodium iodate, creates an inducible swine model of photoreceptor damage.

Our purpose was to find a method to create a large animal model of inducible photoreceptor damage. To this end, we tested in domestic swine the efficacy of two chemical toxins, known to create photoreceptor damage in other species: Iodoacetic Acid (IAA) and Sodium Iodate (NaIO(3)). Intravenous (IV) administration of NaIO(3) up to 90 mg/kg had no effect on retinal function and 110 mg/kg was lethal. IV administration of IAA (5-20 mg/kg) produced concentration-dependent changes in visual function as measured by full-field and multi-focal electroretinograms (ffERG and mfERG), and 30 mg/kg IAA was lethal. The IAA-induced effects measured at two weeks were stable through eight weeks post-injection, the last time point investigated. IAA at 7.5, 10, and 12 mg/kg produce a concentration-dependent reduction in both ffERG b-wave and mfERG N1-P1 amplitudes compared to baseline at all post-injection times. Comparisons of dark- and light-adapted ffERG b-wave amplitudes show a more significant loss of rod relative to cone function. The fundus of swine treated with ≥10 mg/kg IAA was abnormal with thinner retinal vessels and pale optic discs, and we found no evidence of bone spicule formation. Histological evaluations show concentration-dependent outer retinal damage that correlates with functional changes. We conclude that NaIO(3,) is not an effective toxin in swine. In contrast, IAA can be used to create a rapidly inducible, selective, stable and concentration-dependent model of photoreceptor damage in swine retina. Because of these attributes this large animal model of controlled photoreceptor damage should be useful in the investigation of treatments to replace damaged photoreceptors.

Spinal cord injuries containing asymmetrical damage in the ventrolateral funiculus is associated with a higher incidence of at-level allodynia.

UNLABELLED: Approximately 70% of male rats receiving severe T8 spinal contusions develop allodynia in T5-7 dermatomes (at-level) beginning 2 weeks after injury. In contrast, rats having either complete transections or dorsal hemisections do not develop allodynia at-level after chronic spinal cord injury (SCI). In the present study, incomplete laceration and contusion injuries were made to test for neuroanatomical correlates between areas of white matter damage/sparing at the lesion epicenter and the presence/absence of allodynia. After incomplete laceration lesions and 6 weeks of behavioral testing, histological reconstruction and analysis of the lesion epicenters revealed a significant difference (P < .001) in the amount of ventrolateral funiculus (VLF) asymmetry between rats showing pain-like responses evoked by touch (74.5% +/- 8.4% side-to-side difference in VLF damage) versus those not responding to touch (11.3% +/- 4.4% side-to-side difference in VLF damage). A 5-week mean allodynia score for each rat that incorporates a full range of forces that are all innocuous in intact controls revealed that the degree of hypersensitivity at level is related to the extent of VLF asymmetry after SCI. No other damaged spinal white matter or gray matter area was correlated with sensitivity to touch. Similar findings were obtained for rats receiving T8 contusions, a more clinically relevant injury. These data suggest that different extents of damage/sparing between the 2 sides of VLF probably are a requisite for the development of allodynia after SCI. PERSPECTIVE: A side-to-side lesion asymmetry after chronic SCI in a rodent model was found to be highly correlated with the presence and degree of allodynia. Greater insight of key factors contributing to the development and maintenance of chronic neuropathic pain is important for improving quality of life.

Behavioral spectral sensitivity of the zebrafish (Danio rerio).

While the zebrafish (Danio rerio) continues to become an important animal model for the investigation of the genetic and physiological bases of visual processing of the vertebrate retina, its visual behavior, particularly regarding color processing, has received little attention. The purpose of this study was to obtain behavioral spectral sensitivity functions from adult zebrafish using an appetitive instrumental conditioning procedure. A three-chamber maze was implemented to train light-adapted adult zebrafish to swim into the chamber that contained a suprathreshold monochromatic stimulus for a food reward. Visual threshold was determined by varying the stimulus irradiance using a 'two-down one-up' staircase procedure. Threshold values were obtained for wavelengths from 340 to 640 nm. Spectral sensitivity functions obtained show contributions from two nonopponent cone mechanisms (UV and S) and two opponent mechanisms (M-S and L-M). These cone mechanisms are qualitatively similar to those obtained via physiological measures from the On-responses of the zebrafish retina and optic tectum. However, the functions are not quantitatively similar suggesting that further visual processing takes place beyond the processing of the retinal circuitry and processing of the initial stages of the optic tectum. These results demonstrate that the zebrafish is an excellent model to examine and compare the relationship between physiological and behavioral color processing.

Ultraviolet- and short-wavelength cone contributions alter the early components of the ERG of young zebrafish.

The electroretinogram (ERG) is a commonly used measure to examine retinal processing in both basic and clinical research. The purpose of this study was to determine the retinal mechanisms responsible for the developmental differences found in the zebrafish ERG waveform. The ERG of young zebrafish possesses a voltage-negative response to ultraviolet- and short-wavelength stimuli, but not to middle- and long-wavelength stimuli; the ERG of adult zebrafish does not possess this response component. ERGs were obtained from young zebrafish before and after the introduction of either aspartate, or a combination of APB (DL-2-amino-4-phosphonobutyric acid) and PDA (cis-2,3-piperidinedicarboxylic acid) in order to suppress the responses of various types of retinal neurons. Log irradiance versus response amplitude functions of the ERG response to 200-ms stimuli of various wavelengths at various times following stimulus onset (70 and 120 ms) was derived as well as spectral sensitivity. Aspartate eliminated all voltage-positive responses regardless of stimulus wavelength; irradiance-response functions following aspartate were similar to the early responses of young control fish to ultraviolet- and short-wavelength stimuli. APB + PDA produced similar but not identical results as aspartate, suggesting that the combination of these agents does not completely eliminate all post-receptoral contributions to the ERG. Spectral sensitivity functions derived from aspartate-exposed subjects at various time measurements were dominated by contributions from ultraviolet- and short-wavelength-sensitive cone types. These wavelength-dependent ERG responses are similar to those found in humans with enhanced S-cone syndrome. Finally, ERG waveform differences across stimulus wavelength suggest that the circuitry of ultraviolet- and short-wavelength cone types is different to that of middle- and long-wavelength cone types in young zebrafish.