Columbia University Irving Medical Center 2 articles published in JoVE Biology Establishment and Characterization of Patient-derived Gastric Organoids from Biopsies of Benign Gastric Body and Antral Epithelium Kole H. Buckley1, Keely A. Beyries1, Sandra Ryeom2, Sam S. Yoon2, Bryson W. Katona1 1Division of Gastroenterology and Hepatology, University of Pennsylvania Perelman School of Medicine, 2Department of Surgery, Columbia University Irving Medical Center Gastric patient-derived organoids find increasing use in research, yet formal protocols for generating human gastric organoids from single-cell digests with standardized seeding density are lacking. This protocol presents a detailed method for reliably creating gastric organoids from biopsy tissue obtained during upper endoscopy. Biology Imaging of mtHyPer7, a Ratiometric Biosensor for Mitochondrial Peroxide, in Living Yeast Cells Emily Jie-Ning Yang1, Istvan R. Boldogh1,2, Haojie Ji2, Liza Pon1,2, Theresa C. Swayne1,2 1Department of Pathology and Cell Biology, Columbia University Irving Medical Center, 2Confocal and Specialized Microscopy Shared Resource in the Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center Hydrogen peroxide (H2O2) is both a source of oxidative damage and a signaling molecule. This protocol describes how to measure mitochondrial H2O2 using mitochondria-targeted HyPer7 (mtHyPer7), a genetically encoded ratiometric biosensor, in living yeast. It details how to optimize imaging conditions and perform quantitative cellular and subcellular analysis using freely available software.