Data and Code for paper: Basement membrane turnover controls cell shapeRicardo Barrientos1,2,, Billie Meadowcroft1,2,3, Besaiz J. Sánchez-Sánchez4, Brian M. Stramer4, Ewa K. Paluch5, Guillaume Charras2,6,7, Shiladitya Banerjee8, Andela Saric3, Yanlan Mao1,2,(1) UCL Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK.(2) Institute for the Physics of Living Systems, University College London, Gower Street, London WC1E 6BT, UK.(3) Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria.(4) Randall Centre for Cell and Molecular Biophysics, King’s College London, SE1 1UL London, UK.(5) Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK.(6) London Centre for Nanotechnology, 17-19 Gordon street, London WC1H 0AH, UK.(7) Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.(8) School of Physics, Georgia Institute of Technology, Atlanta, GA 30306, USA.* Correspondence: ricardo.barrientos.14@ucl.ac.uk (R.B.), y.mao@ucl.ac.uk (Y.M.)SummaryThe regulation of 3D cell shape is a fundamental problem of life. In multicellular tissues, cell shape emerges through the balance of forces inside and outside the cell. In epithelia, the basement membrane (BM) is the first extracellular barrier that cells sense biochemically and mechanically. Despite this, little is known about how BM mechanical properties are regulated and how they impact cell shape. Through mathematical modelling, we show that the stress relaxation time of the BM can regulate cell shape. Using molecular dynamics simulations, we show that the stress relaxation time of a collagen IV network can be inferred from the lifetime of collagen IV molecules. To measure collagen IV lifetime in vivo, we develop a fluorescent timer reporter for collagen IV and show that perlecan modifies collagen IV lifetime. This cross-disciplinary approach establishes a multiscale framework to probe matrix protein turnover, their regulation and function in cell shape control.