Imaging heterochromatin in human embryonic stem cells with light-sheet Bayesian microscopy

In eukaryotic cells, chromatin is organized into two distinct domains: lightly packed, and actively transcribed euchromatin, and highly condensed, and transcriptionally silent heterochromatin. However, despite its importance, the architecture of heterochromatin remains elusive, due to the lacking of powerful tools. We present a new, Light-Sheet Bayesian Super-resolution Microscope (LSB-SRM) that allows direct visualization of nuclear structures in human embryonic stem cells (hESs). This microscope is a marriage between two recently developed techniques: light-sheet single molecule super-resolution microscopy and Bayesian super-resolution image reconstruction algorithm. The light-sheet illumination reduces the excitation volume, suppresses the fluorescence background from fluorophore in unwanted layer of a sample, and therefore increases the signal-to-noise ratio of the single-molecule detection. The Bayesian algorithm can efficiently resolve single molecules in images with noisy background. A combination of the two allows us to directly visualize heterochromatic structures in the nucleus of human embryonic stem cells at super-resolution.