Emergence of Patterned Stem Cell Differentiation within Multicellular Structures

¹ Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA; Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA
² Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA

^* To whom correspondence should be addressed. E-mail: chrischen{at}seas.upenn.edu.

	Abstract

The ability of stem cells to differentiate into specified lineages in the appropriate locations is vital to morphogenesis and adult tissue regeneration. While soluble signals are important regulators of patterned differentiation, here we show that gradients of mechanical forces can also drive patterning of lineages. In the presence of soluble factors permitting osteogenic and adipogenic differentiation, human mesenchymal stem cells at the edge of multicellular islands differentiate into the osteogenic lineage, while those in the center became adipocytes. Interestingly, changing the shape of the multicellular sheet modulated the locations of osteogenic versus adipogenic differentiation. Measuring traction forces revealed gradients of stress that preceded and mirrored the patterns of differentiation, where regions of high stress resulted in osteogenesis while stem cells in regions of low stress differentiated to adipocytes. Inhibiting cytoskeletal tension suppressed the relative degree of osteogenesis versus adipogenesis, and this spatial patterning of differentiation was also present in threedimensional multicellular clusters. These findings demonstrate a role for mechanical forces in linking multicellular organization to spatial differentials of cell differentiation, and represent an important guiding principle in tissue patterning that could be exploited in stem cell-based therapies.