Adhesion-contractile balance in myocyte differentiation

Abstract

Tissue cells generally pull on their matrix attachments and balance a quasi-static contractility against adequate adhesion, but any correlation with and/or influence on phenotype are not yet understood. Here, we begin to demonstrate how differentiation state couples to actomyosin-based contractility through adhesion and substrate compliance. Myotubes are differentiated from myoblasts on collagen-patterned coverslips that allow linear fusion but prevent classic myotube branching. Post-fusion, myotubes adhere to the micro-strips but lock into a stress fiber-rich state and do not differentiate significantly further. In contrast, myotubes grown on top of such cells do progress through differentiation, exhibiting actomyosin striations within one week. A compliant adhesion to these lower cells is suggested to couple to contractility and accommodate the reorganization needed for upper cell striation. Contractility is assessed in these adherent cells by mechanically detaching one end of the myotubes. All myotubes, whether striated or not, shorten with an exponential decay. The cell-on-cell myotubes relax more, which implies a greater contractile stress. The non-muscle myosin II inhibitor blebbistatin inhibits relaxation for either case. Myotubes in culture are thus clearly prestressed by myosin II, and this contractility couples to substrate compliance and ultimately influences actomyosin striation.

Cellular self-organization by autocatalytic alignment feedback

“…However, we do not rule out the possibility that the cells in the unpatterned areas might influence the twitching behavior and sarcomere development. Another factor that has been reported to be relevant to sarcomere development is adhesion (Engler et al, 2004a;Griffen et al, 2004;Sen et al, 2011). In our experiments, cell adhesion to patterned substrates was not investigated during the alignment process, although we observed that alignment as guided by patterns did not differ between different cell layers, when present.…”

Compliance-induced adherens junction formation in epithelial cells and tissues is regulated by JNK

“…Therefore, the basal cells may be sensing a more rigid substrate (dermis) as compared to the suprabasal and granular cells residing on other, softer epidermal cell layers. This 'cell-on-cell' hypothesis was initially proposed by Discher and colleagues who observed that myotubes attaching on glass showed abundant stress fibers but myotubes cultured on top of another myotube layer differentiated into a striated state, presumably because they perceived a softer substrate (Engler et al, 2004;Griffin et al, 2004). This stiffness gradient across the epidermal tissue may in turn be responsible for downregulating JNK phosphorylation leading to AJ formation in the upper epidermal layers.…”

Material‐Driven Fibronectin Assembly Promotes Maintenance of Mesenchymal Stem Cell Phenotypes

“…Forces generated by cells regulate different processes including cell contraction and differentiation, [ 34 ] and cell migration [ 35 ] via phosphorylation of the myosin light chain (MLC). [ 36 ] We examined whether this contractility process was related to differentiation or self-renewal of mMSCs cultured on PEA and PMA.…”