The p53 tumor suppressor protein is a transcriptional activator, which can mediate apoptotic cell death in a variety of cell types. To determine whether sequence-specific trans-activation is a prerequisite for the induction of apoptosis by p53, the apoptotic effects of various p53 deletion mutants were monitored in an assay based on the transient transfection of HeLa cells. A truncated protein (p53d1214), containing only the first 214 amino-terminal residues of murine p53, induced extensive apoptosis, albeit at a slower rate than trans-activation-competent wild-type p53. p53d1214 also suppressed the transformation of rat fibroblasts by several oncogene combinations and particularly by myc plus ras and HPV E7 plus ras. p53d1214 lacks a major portion of the DNA-binding domain and cannot activate p53-responsive promoters. Moreover, a human p53 protein carrying mutations in residues 22 and 23 also triggered HeLa cell apoptosis, despite failing to induce significant activation of relevant p53 target promoters. These data suggest the existence of two p53-dependent apoptotic pathways--one requiring activation of specific target genes, and the other independent of sequence-specific trans-activation. The latter pathway may actually be totally uncoupled from the binding of p53 to its consensus DNA sites. The relative contribution of trans-activation-independent apoptosis to tumor suppression by p53 may be dictated by the specific genetic lesions present in the particular tumor.

Chx10 is a homeobox-containing transcription factor critical for progenitor cell proliferation and bipolar cell determination in the developing retina. Its expression in the retina has been reported to be restricted to these cell populations. To further understand Chx10 regulation and function, a multifunctional reporter construct consisting of GFP, alkaline phosphatase, and Cre recombinase was integrated into a BAC encoding Chx10. Stable lines of transgenic mice expressing this BAC were generated and analyzed. The reporter expression was faithful to the endogenous retinal Chx10 expression pattern and revealed a previously unappreciated locus of Chx10 expression in a subset of Müller glial cells. In addition, Chx10 reporter activity was identified in mature orJ-Chx10 mutant retinas, although these retinas lack Chx10-expressing bipolar cells. Reporter and molecular analysis showed that the reporter-expressing cells in the mutant had hallmarks of progenitor cells or partially differentiated Müller glial cells. These results strongly suggest that Chx10 promotes bipolar fate by affecting differentiation of late progenitor cells. Crosses of the Chx10 BAC reporter mice to R26R mice for fate-mapping experiments revealed that Chx10 reporter-expressing progenitor cells contribute to all mature cell types of the retina. These results demonstrate the utility of these lines for generation of mosaic or complete genetic manipulations of the retina.

The p53 tumor‐suppressor gene product is frequently inactivated in malignancies by point mutation. Although most tumor‐derived p53 mutants show loss of sequence specific transcriptional activation, some mutants have been identified which retain this activity. One such mutant, p53175P, is defective for the suppression of transformation in rodent cells, despite retaining the ability to suppress the growth of p53‐null human cells. We now demonstrate that p53175P can induce a cell‐cycle arrest in appropriate cell types but shows loss of apoptotic function. Our results therefore support a direct role of p53 transcriptional activation in mediating a cell‐cycle arrest and demonstrate that such activity is not sufficient for the full apoptotic response. These data suggest that either p53 can induce apoptosis through a transcriptionally independent mechanism, a function lost by p53175P, or that this mutant has specifically lost the ability to activate genes which contribute to cell death, despite activation of genes responsible for the G1 arrest. This dissociation of the cell‐cycle arrest and apoptotic activities of p53 indicates that inactivation of p53 apoptotic function without concomitant loss of growth inhibition can suffice to relieve p53‐dependent tumor‐suppression in vivo and thereby contribute to tumor development.

Age-related macular degeneration (AMD) is the major cause of blindness in developed nations. AMD is characterized by retinal pigmented epithelial (RPE) cell dysfunction and loss of photoreceptor cells. Epidemiologic studies indicate important contributions of dietary patterns to the risk for AMD, but the mechanisms relating diet to disease remain unclear. Here we investigate the effect on AMD of isocaloric diets that differ only in the type of dietary carbohydrate in a wild-type aged-mouse model. The consumption of a high-glycemia (HG) diet resulted in many AMD features (AMDf), including RPE hypopigmentation and atrophy, lipofuscin accumulation, and photoreceptor degeneration, whereas consumption of the lower-glycemia (LG) diet did not. Critically, switching from the HG to the LG diet late in life arrested or reversed AMDf.LG diets limited the accumulation of advanced glycation end products, long-chain polyunsaturated lipids, and their peroxidation end-products and increased C3-carnitine in retina, plasma, or urine. Untargeted metabolomics revealed microbial cometabolites, particularly serotonin, as protective against AMDf. Gut microbiota were responsive to diet, and we identified microbiota in the Clostridiales order as being associated with AMDf and the HG diet, whereas protection from AMDf was associated with the Bacteroidales order and the LG diet. Network analysis revealed a nexus of metabolites and microbiota that appear to act within a gut-retina axis to protect against diet-and age-induced AMDf. The findings indicate a functional interaction between dietary carbohydrates, the metabolome, including microbial cometabolites, and AMDf. Our studies suggest a simple dietary intervention that may be useful in patients to arrest AMD.age-related macular degeneration | glycemic index | advanced glycation end-product | gut microbiome | metabolomics A ge-related macular degeneration (AMD) is the leading cause of irremediable blindness in the industrialized world, with 200 million cases projected by 2020, at a cost of $300 billion (1, 2). Dry AMD accounts for the great majority of cases and is associated with photoreceptor cell loss, often preceded by compromise to the retina pigment epithelium (RPE) cells that nourish and remove waste from the photoreceptors. The etiology of AMD remains an enigma but is clearly multifactorial. Stresses associated with AMD include environment, age, and genetics (3). Frustratingly, there are no early biomarkers to anticipate AMD, and there are no therapies or cure.Recently, we and others observed in epidemiologic studies that, in addition to micronutrients (4-6), macronutrient quality [e.g., consuming a diet with a high glycemic index (GI)] is a significant risk factor for AMD onset and/or progress in nondiabetic humans (7)(8)(9). The GI appears to be an attractive dietary intervention target, because simple replacement of small amounts of high-index foods (such as white bread) with lower-index foods (such as wholegrain bread) can significantly reduce glycemic peaks without requiring ...