Characterization of connective tissue progenitors through phase contrast and multicolor fluorescence time-lapse microscopy

Abstract

Connective tissue progenitors (CTPs) are defined as the heterogeneous population of tissue resident stem and progenitor cells capable of proliferating and differentiating into connective tissue phenotypes. The prevalence and variation in clonal progeny of CTPs can be characterized using a colony formation assay. However, colony assays do not directly assess the characteristics of the colony founding CTP. We developed a large field of view, time lapse microscopy system with phase contrast and fluorescence capabilities that enables tracking from seeding through colony formation. Cells derived from the trabecular surface of bone were prepared and seeded in an Ibidi-Ph+ chamber slide. Phase contrast images of the slide were obtained every hour using a DMI6000 Leica microscope, 10X objective, and Retiga 2000R camera. Cells were stained using fluorescent antibodies for multiple markers at the time of plating to determine marker expression on seeded cells and re-stained to determine expression on their progeny. Colonies were identified and characterized using automated image processing and quantitative analysis methods. Following colony identification, the time lapse was reversed to identify and characterize the colony founding CTP according to morphology and marker expression. As a representative example, a CD73 + /CD90 - /CD105 - and a CD73 + /CD90 + /CD105 - CTP resulted in a colony with an area of 3720826 microns 2 and percent area expression of 2.98%, 3.62%, and 1.13% for CD73, CD90, and CD105, respectively. This method can be used to study CTPs and other stem and progenitor cell populations to benefit point-of-care methods for assay and isolation in cell based therapies.