Abstract
IntroductionIn vivo, cells are surrounded by extracellular matrix (ECM). To build organs from single cells, it is generally believed that ECM serves as scaffolds to coordinate cell positioning and differentiation. Nevertheless, how cells utilize cell‐ECM interactions for the spatiotemporal coordination to different ECM at the tissue scale is not fully understood.MethodsHere, using in vitro assay with engineered MDCK cells expressing H2B‐mCherry (nucleus) and gp135/Podocalyxin‐GFP (apical marker), we show in multi‐dimensions that such coordination for epithelial morphogenesis can be determined by cell‐soluble ECM interaction in the fluidic phase.ResultsThe coordination depends on the native topology of ECM components such as sheet‐like basement membrane (BM) and type I collagen (COL) fibres: scaffold formed by BM (COL) facilitates a close‐ended (open‐ended) coordination that leads to the formation of lobular (tubular) epithelium. Further, cells form apicobasal polarity throughout the entire lobule/tubule without a complete coverage of ECM at the basal side, and time‐lapse two‐photon scanning imaging reveals the polarization occurring early and maintained through the lobular expansion. During polarization, gp135‐GFP was converged to the apical surface collectively in the lobular/tubular structures, suggesting possible intercellular communications. Under suspension culture, the polarization was impaired with multi‐lumen formation in the tubules, implying the importance of ECM biomechanical microenvironment.ConclusionOur results suggest a biophysical mechanism for cells to form polarity and coordinate positioning at tissue scale, and in engineering epithelium through cell‐soluble ECM interaction and self‐assembly.
Highlights
In vivo, cells are surrounded by extracellular matrix (ECM)
Over the past few decades, studies on epithelial morphogenesis have indicated the importance of cell-cell adhesions and cell-extracellular matrix (ECM) interactions.5,9-16 The differentiation of epithelial cells in which non-polarized cells form polarized epithelium depends on ECM components.[9]
Laminin immuno-staining showed the distribution of ECM scaffold around the polarized lumen (Figure 5D), and laminin only covered the lateral sides of lobules, not at their top or bottom sides (Figure 5D), which seemed similar to the results found in the lobules cultured on top of basement membrane (BM) gels (Figure 3C)
Summary
One feature in epithelial development and regeneration is the spatiotemporal coordination of cell positioning and differentiation.[1]. To form long-range coordination, it is generally believed that ECM can serve as scaffolds to guide cell positioning and polarization.[15] Cells constantly secrete soluble ECM molecules and degrade existing ECM scaffolds into soluble fragments in vivo. We study whether ECM scaffolds created by ECM self-assembled hydrogel or by cell-mediated assembly play the primary roles in the formation and coordination of epithelial morphogenesis. These two processes can hardly be decoupled in vivo or through the conventional ECM reconstitution approaches. Our results suggest a potential mechanism which cells can use to form polarity and coordinate morphogenesis in vivo, and a strategy to engineer epithelial structures through self-assembly in vitro
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