Mechanical force regulates integrin turnover in Drosophila in vivo

Abstract

Regulated assembly and disassembly, or turnover, of integrin-mediated cell-extracellular matrix (ECM) adhesions is essential for dynamic cell movements and long-term tissue maintenance. For example, in Drosophila, misregulation of integrin turnover disrupts muscle-tendon attachment at myotendinous junctions (MTJs). We demonstrate that mechanical force, which modulates integrin activity, also regulates integrin and intracellular adhesion complex (IAC) turnover in vivo. Using conditional mutants to alter the tensile force on MTJs, we found that the proportion of IAC components undergoing turnover inversely correlated with the force applied on MTJs. This effect was disrupted by point mutations in β-integrin that interfere with ECM-induced conformational changes and activation of β-integrin or integrin-mediated cytoplasmic signalling. These mutants also disrupted integrin dynamics at MTJs during larval development. Together, these data suggest that specific β-integrin-mediated signals regulate adhesion turnover in response to tension during tissue formation. We propose that integrin-ECM adhesive stability is continuously controlled by force in vivo through integrin-dependent auto-regulatory feedback mechanisms so that tissues can quickly adapt to and withstand mechanical stresses.

Tension regulates myosin dynamics during Drosophila embryonic wound repair

“…To understand how myosin turns over at the wound edge, we developed a mathematical model to extract the rates of myosin assembly (k on ) and disassembly (k off ) in the photobleached regions (Pines et al, 2012). Using the model, we estimated the assembly rate constant at the purse string to be 0.012±0.003 s −1 , significantly lower than the 0.050±0.015 s −1 in epidermal cables (P<0.01, Fig.…”

“…We modelled FRAP using a two-state model (Pines et al, 2012) to describe the association and dissociation of myosin to and from the purse string, with rate constants k on and k off , respectively:…”

In vivo regulation of integrin turnover by outside-in activation

“…Intriguing evidence from Drosophila, using a sensor for integrin activation, has suggested that Mn 2+ might be able to activate integrins in vivo, in larval imaginal discs (Helsten et al, 2008). Moreover, reverse and forward genetic approaches in the fly have identified point mutations in Talin and the β-integrin subunit (known as βPS integrin) that have been proposed to modulate activation (Ellis et al, 2014(Ellis et al, , 2011Jannuzi et al, 2002Jannuzi et al, , 2004Pines et al, 2012Pines et al, , 2011Tanentzapf and Brown, 2006).…”

“…Furthermore, clathrin-mediated endocytosis is essential for turnover and consequently for maintaining adhesions at the MTJs (Yuan et al, 2010). Experiments using inducible mutations that either increased or decreased the mechanical force applied on MTJs have shown that force is a potent regulator of integrin adhesion complex turnover (Hakonardottir et al, 2015;Pines et al, 2012). Increased force results in decreased endocytosis of integrins and an increase in the rate of assembly of new adhesions, which together combine to stabilize integrin-based adhesions (Hakonardottir et al, 2015;Pines et al, 2012).…”

“…The Drosophila MTJs serve as a powerful model to study the turnover of integrins and their adhesion complex in the context of living intact animals. The turnover of wild-type and point-mutated tagged components of the integrin adhesion complex is analyzed at the MTJ using fluorescence recovery after photobleaching (FRAP) and mathematical modeling (Hakonardottir et al, 2015;Pines et al, 2012;Yuan et al, 2010). Previous work has established that, in fly MTJs, FRAP recovery is mostly due to endocytosis and exocytosis of integrin rather than their lateral diffusion (Yuan et al, 2010).…”