Computationally Enhanced Quantitative Phase Microscopy Reveals Autonomous Oscillations in Mammalian Cell Growth

The fine balance of growth and division is a fundamental property of the physiology of cells and one of the least understood. Its study has been thwarted by difficulties in the accurate measurement of cell size and the even greater challenges of measuring growth of a single-cell over time. We address these limitations by demonstrating a new computationally enhanced methodology for Quantitative Phase Microscopy (ceQPM) for adherent cells, using improved image processing algorithms and automated cell tracking software. Accuracy has been improved more than two-fold and this improvement is sufficient to establish the dynamics of cell growth and adherence to simple growth laws. It is also sufficient to reveal unknown features of cell growth previously unmeasurable. With these methodological and analytical improvements, we document a remarkable oscillation in growth rate in several different cell lines, occurring throughout the cell cycle, coupled to cell division or birth, and yet independent of cell cycle progression. We expect that further exploration with this improved tool will provide a better understanding of growth rate regulation in mammalian cells. Significance Statement It has been a long-standing question in cell growth studies that whether the mass of individual cell grows linearly or exponentially. The two models imply fundamentally distinct mechanisms, and the discrimination of the two requires great measurement accuracy. Here, we develop a new method of computationally enhanced Quantitative Phase Microscopy (ceQPM), which greatly improves the accuracy and throughput of single-cell growth measurement in adherent mammalian cells. The measurements of several cell lines indicate that the growth dynamics of individual cells cannot be explained by either of the simple models but rather present an unanticipated and remarkable oscillatory behavior, suggesting more complex regulation and feedbacks.