Nanometer-Scale Resolution Achieved with Nonradiative Excitation
ACS PHOTONICS
Authors: Riachy, Lina; El Arawi, Dalia; Jaffiol, Rodolphe; Vezy, Cyrille
Abstract
Nonradiative excitation fluorescence microscopy (NEFM) is a promising technique allowing the observation of biological samples beyond the diffraction limit. By coating a substrate with an homogeneous monolayer of quantum dots (QDs), NEFM is achieved through a nonradiative energy transfer from QDs (donors) to dye molecules located in the sample (acceptors). The excitation depth of the sample is then given by the Forster radius, which corresponds to a few nanometers above the surface. The powerful axial resolution of NEFM is highlighted by observing the adhesion of giant unilamellar vesicles (GUVs) on strong interaction with coated surfaces. In this paper, we demonstrate that the QD-quenching level is valuable to calculate and map the distance between the membrane and the surface with a high precision along the optical axis. By tuning the electrostatic interactions between the membrane and the substrate, we have been able to measure a height displacement of approximate to 1 nm of the lipid membrane. The experimental results were discussed according to simulations, which take into account all the common forces appearing between lipid membranes and surfaces.
Reduced Representation Bisulfite Sequencing Determination of Distinctive DNA Hypermethylated Genes in the Progression to Colon Cancer in African Americans
GASTROENTEROLOGY RESEARCH AND PRACTICE
Authors: Ashktorab, Hassan; Shakoori, Afnan; Zarnogi, Shatha; Sun, Xueguang; Varma, Sudhir; Lee, Edward; Shokrani, Babak; Laiyemo, Adeyinka O.; Washington, Kareem; Brim, Hassan
Abstract
Background and Aims. Many studies have focused on the determination of methylated targets in colorectal cancer. However, few analyzed the progressive methylation in the sequence from normal to adenoma and ultimately to malignant tumors. This is of utmost importance especially in populations such as African Americans who generally display aggressive tumors at diagnosis and for whom markers of early neoplasia are needed. We aimed to determine methylated targets in the path to colon cancer in African American patients using Reduced Representation Bisulfite Sequencing (RRBS). Methods. Genomic DNA was isolated from fresh frozen tissues of patients with different colon lesions: normal, a tubular adenoma, a tubulovillous adenoma, and five cancers. RRBS was performed on these DNA samples to identify hypermethylation. Alignment, mapping, and confirmed CpG methylation analyses were performed. Preferential hypermethylated pathways were determined using Ingenuity Pathway Analysis (IPA). Results. We identified hypermethylated CpG sites in the following genes: L3MBTL1, NKX6-2, PREX1, TRAF7, PRDM14, and NEFM with the number of CpG sites being 14, 17, 10, 16, 6, and 6, respectively, after pairwise analysis of normal versus adenoma, adenoma versus cancer, and normal versus cancer. IPA mapped the above-mentioned hypermethylated genes to the Wnt/ beta-catenin, PI3k/AKT, VEGF, and JAK/STAT3 signaling pathways. Conclusion. This work provides insight into novel differential CpGs hypermethylation sites in colorectal carcinogenesis. Functional analysis of the novel gene targets is needed to confirm their roles in their associated carcinogenic pathways.