Polysialylated - neural cell adhesion molecule (PSA-NCAM) promotes recovery of vision after the critical period.

Vision loss has long since been considered irreversible after a critical period; however, there is potential to restore limited vision, even in adulthood. This phenomenon is particularly pronounced following complete loss of vision in the dominant eye. Adult neural cell adhesion molecule (NCAM) knockout mice have an age-related impairment of visual acuity. The underlying cause of early deterioration in visual function remains unknown. Polysialylated (PSA) NCAM is involved in different forms of neural plasticity in the adult brain, raising the possibility that NCAM plays a role in the plasticity of the visual cortex, and therefore, in visual ability. Here, we examined whether PSA-NCAM is required for visual cortical plasticity in adult C57Bl/6J mice following deafferentation and long-term monocular deprivation. Our results show that elevated PSA in the contralateral visual cortex of the reopened eye is accompanied by changes in other markers of neural plasticity: increased brain-derived neurotrophic factor (BDNF) levels and degradation of perineuronal nets (PNNs). The removal of PSA-NCAM in the visual cortex of these mice reduced BDNF expression, decreased PNN degradation, and resulted in impaired recovery of visual acuity after optic nerve transection and chronic monocular deprivation. Collectively, our results demonstrate that PSA-NCAM is necessary for the reactivation of visual cortical plasticity and recovery of visual function in adult mice. It also offers a potential molecular target for the therapeutic treatment of cortically based visual impairments.

Polysialylated Neural Cell Adhesion Molecule Protects Against Light-Induced Retinal Degeneration.

PURPOSE: We previously demonstrated that neural cell adhesion molecule (NCAM) plays an important role in supporting the survival of injured retinal ganglion cells. In the current study, we used light-induced retinal degeneration (LIRD) as a model to investigate whether NCAM plays a functional role in neuroprotection and whether NCAM influences p75NTR signaling in modulating retinal cell survival. METHODS: Retinas from wild-type (WT) and NCAM deficient (-/-) mice were tested by electroretinogram before and after LIRD, and changes in the protein expressions of NCAM, polysialic acid (PSA)-NCAM, p75NTR, and active caspase 3 were measured by immunoblot from 0 to 4 days after light induction. The effects of NCAM and PSA-NCAM on p75NTR were examined by intraocular injections of the p75NTR function-blocking antibody and/or the removal of PSA with endoneuraminidase-N prior to LIRD. RESULTS: In WT mice, low levels of active caspase 3 activation were detected on the first day, followed by increases up to 4 days after LIRD. Conversely, in NCAM-/- mice, higher cleaved caspase 3 levels along with rapid reductions in electroretinogram amplitudes were found earlier at day 1, followed by reduced levels by day 4. The removal of PSA prior to LIRD induced earlier onset of retinal cell death, an effect delayed by the coadministration of endoneuraminidase-N and the p75NTR function-blocking antibody antiserum. CONCLUSIONS: These results indicate that NCAM protects WT retinas from LIRD; furthermore, the protective effect of NCAM is, at least in part, attributed to its effects on p75NTR.

Effect of NCAM on aged-related deterioration in vision.

The neural cell adhesion molecule (NCAM) is involved in developmental processes and age-associated cognitive decline; however, little is known concerning the effects of NCAM in the visual system during aging. Using anatomical, electrophysiological, and behavioral assays, we analyzed age-related changes in visual function of NCAM deficient (-/-) and wild-type mice. Anatomical analyses indicated that aging NCAM -/- mice had fewer retinal ganglion cells, thinner retinas, and fewer photoreceptor cell layers than age-matched controls. Electroretinogram testing of retinal function in young adult NCAM -/- mice showed a 2-fold increase in a- and b-wave amplitude compared with wild-type mice, but the retinal activity dropped dramatically to control levels when the animals reached 10 months. In behavioral tasks, NCAM -/- mice had no visual pattern discrimination ability and showed premature loss of vision as they aged. Together, these findings demonstrate that NCAM plays significant roles in the adult visual system in establishing normal retinal anatomy, physiology and function, and in maintaining vision during aging.

Yin Yang 1 physically interacts with Hoxa11 and represses Hoxa11-dependent transcription.

Yin Yang 1 (YY1) plays an indispensable role in embryonic development. YY1 contains an evolutionarily conserved, 22-amino acid segment, the PHO homology region (PHR), which is located within its central domain (spacer) and has been shown previously to participate in the recruitment of Polycomb group of proteins and in YY1-mediated transcription. In this report, we show that the PHR physically interacts with several Abd-B-type Hox proteins. Although ectopic expression of Hoxa11 enhanced target promoter activity, overexpression of YY1 repressed this effect, which was abrogated by YY1 siRNA and the histone deacetylase inhibitor trichostatin A. We have further demonstrated that this suppression effect was the result of YY1-dependent recruitment of HDAC2 to the Hoxa11 target promoter. Taken together, our findings show that YY1 represses Hoxa11-dependent transcription via interactions with the Hox proteins and HDAC recruitment, providing a link between an Abd-type Hox protein and a Polycomb group protein at the level of direct protein-protein interactions. These findings not only provide a novel insight into YY1 function but also identify a new regulation of homeotic protein-mediated transcriptional regulation in general.

Targeted ablation of Par-4 reveals a cell type-specific susceptibility to apoptosis-inducing agents.

The prostate apoptosis response-4 (Par-4) protein has been shown to function as an effector of cell death in response to various apoptotic stimuli, and down-regulation of this protein has been suggested to be a key event during tumorigenesis. Several studies suggest an essential function for the COOH-terminal leucine repeats/death domain of Par-4 in mediating apoptosis. We investigated the biological role of this domain in vivo by generating knock-out mice expressing a Par-4 mutant protein lacking the COOH terminus domain. We found that the Par-4 mutant mice are viable and fertile with no overt phenotype, thus excluding an essential role for the COOH terminus domain of Par-4 in embryogenesis and developmental apoptosis. To determine the requirement of Par-4 for apoptosis, we treated primary fibroblasts with various stimuli that trigger mitochondria and membrane receptor cell death pathways. Fibroblasts isolated from Par-4 mutant mice are as sensitive as the wild-type cells to these apoptosis-inducing agents. Similar effects were observed following RNA interference (RNAi)-mediated knockdown of Par-4 in these cells. In contrast, RNAi-mediated depletion of Par-4 in HeLa cells resulted in a significant inhibition of apoptosis induced by various proapoptotic agents. Taken together, our findings provide strong genetic evidence that the proapoptotic function of Par-4 is dependent on the cellular context and raise the possibility that alterations of Par-4 function may occur during carcinogenesis.

Par-4 links dopamine signaling and depression.

Prostate apoptosis response 4 (Par-4) is a leucine zipper containing protein that plays a role in apoptosis. Although Par-4 is expressed in neurons, its physiological role in the nervous system is unknown. Here we identify Par-4 as a regulatory component in dopamine signaling. Par-4 directly interacts with the dopamine D2 receptor (D2DR) via the calmodulin binding motif in the third cytoplasmic loop. Calmodulin can effectively compete with Par-4 binding in a Ca2+-dependent manner, providing a route for Ca2+-mediated downregulation of D2DR efficacy. To examine the importance of the Par-4/D2DR interaction in dopamine signaling in vivo, we used a mutant mouse lacking the D2DR interaction domain of Par-4, Par-4DeltaLZ. Primary neurons from Par-4DeltaLZ embryos exhibit an enhanced dopamine-cAMP-CREB signaling pathway, indicating an impairment in dopamine signaling in these cells. Remarkably, Par-4DeltaLZ mice display significantly increased depression-like behaviors. Collectively, these results provide evidence that Par-4 constitutes a molecular link between impaired dopamine signaling and depression.

Coordinated histone modifications mediated by a CtBP co-repressor complex.

The transcriptional co-repressor CtBP (C-terminal binding protein) is implicated in tumorigenesis because it is targeted by the adenovirus E1A protein during oncogenic transformation. Genetic studies have also identified a crucial function for CtBP in animal development. CtBP is recruited to DNA by transcription factors that contain a PXDLS motif, but the detailed molecular events after the recruitment of CtBP to DNA and the mechanism of CtBP function in tumorigenesis are largely unknown. Here we report the identification of a CtBP complex that contains the essential components for both gene targeting and coordinated histone modifications, allowing for the effective repression of genes targeted by CtBP. Inhibiting the expression of CtBP and its associated histone-modifying activities by RNA-mediated interference resulted in alterations of histone modifications at the promoter of the tumour invasion suppressor gene E-cadherin and increased promoter activity in a reporter assay. These findings identify a molecular mechanism by which CtBP mediates transcriptional repression and provide insight into CtBP participation in oncogenesis.