A New Strategy to Identify and Annotate Human RPE-Specific Gene Expression

Background: To identify and functionally annotate cell type-specific gene expression in the human retinal pigment epithelium (RPE), a key tissue involved in age-related macular degeneration and retinitis pigmentosa. Methodology: RPE, photoreceptor and choroidal cells were isolated from selected freshly frozen healthy human donor eyes using laser microdissection. RNA isolation, amplification and hybridization to 44 k microarrays was carried out according to Agilent specifications. Bioinformatics was carried out using Rosetta Resolver, David and Ingenuity software. Principal Findings: Our previous 22 k analysis of the RPE transcriptome showed that the RPE has high levels of protein synthesis, strong energy demands, is exposed to high levels of oxidative stress and a variable degree of inflammation. We currently use a complementary new strategy aimed at the identification and functional annotation of RPE-specific expressed transcripts. This strategy takes advantage of the multilayered cellular structure of the retina and overcomes a number of limitations of previous studies. In triplicate, we compared the transcriptomes of RPE, photoreceptor and choroidal cells and we deduced RPE specific expression. We identified at least 114 entries with RPE-specific gene expression. Thirty-nine of these 114 genes also show high expression in the RPE, comparison with the literature showed that 85% of these 39 were previously identified to be expressed in the RPE. In the group of 114 RPE specific genes there was an overrepresentation of genes involved in (membrane) transport, vision and ophthalmic disease. More fundamentally, we found RPE-specific involvement in the RAR-activation, retinol metabolism and GABA receptor signaling pathways. Conclusions: In this study we provide a further specification and understanding of the RPE transcriptome by identifying and analyzing genes that are specifically expressed in the RPE

The Price Impact of Trades in Illiquid Stocks in Periods of High and Low Market Activity

Using high frequency data on ten infrequently traded stocks listed on the NYSE in the year 1999, we measure the information content of a trade and its relation to the trading intensity. While the price impact curve for frequently traded stocks monotonically increases towards the full information price, we find impulse response functions that first ‘overshoot ’ and subsequently decrease towards the full information price. The overshooting effect strongly depends upon the bid-ask spread and the trading intensity, and is explained by several market microstructure theories. Furthermore, we show that the difference in price impact between periods of slow and fast trading is much larger for illiquid stocks than for frequently traded stocks. We model the overnight behavior of the trading intensity and returns and show that durations persist overnight. Additionally, we show that, for infrequently traded stocks, it may take several days before the full information price that follows a trade is attained, even in periods of relatively high market activity. Moreover, the adjustment time crucially depends upon the bid-ask spread and the trading intensity