Dry Mass and Cell Cycle Follow-Up from Quantitative Phase Imaging

Abstract

During cell cycle, a cell doubles all its components and divides into two cells. Cell cycle is often studied with fluorescent labeling, by flow cytometry. Here, we propose a simple method to analyze cell cycle and dry mass fluctuations using quantitative phase imaging.The technique is based on a quadri-wave lateral shearing interferometry (QWLSI) wave front sensor [1]. It provides a quantitative measurement of the optical path difference (OPD = Δn•thickness) in nm. This measurement, when integrated over the cell surface, is directly proportional to the cell dry mass [2], giving direct information on the cell growth. No labeling is needed. It is self-referenced and can be plugged on any microscope with classic objectives, a white light and a camera port. Since it is achromatic, it can be used in near IR for long live cell imaging. It can easily be combined with fluorescence for simultaneous correlative microscopy. Automated segmentation of cells is easy due to the absence of halo or artifacts. It is fast (camera frame-rate limited) and sensitive (diffraction-limited in X and Y, ± 0.5 nm in OPD, ± 0.6 pg for a 570 pg cell).We established criteria integrating both dry mass and morphological parameters to identify different cell cycle stages and growth rate of haploid and diploid yeasts, as well as four different mammalian cell lines, under different conditions. We studied them by time lapse and population snapshot imaging. The method is robust to record cellular division processes and effects of drugs on cell growth.[1] P Bon, G Maucort, B Wattellier and S Monneret, “Quadriwave lateral shearing interferometry for quantitative phase microscopy of living cells”, Optics Express, 17 (15): 13080-13094 (2009).[2] R Barer, “Interference microscopy and mass determination”, Nature, 169: 366-367 (1952).