Jocelyn Etienne<p>Studying the relationship between the size and the <a href="https://scicomm.xyz/tags/anatomy" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>anatomy</span></a> and <a href="https://scicomm.xyz/tags/physiology" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>physiology</span></a> of <a href="https://scicomm.xyz/tags/living" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>living</span></a> organisms has proven useful in order to decipher what the key <a href="https://scicomm.xyz/tags/physical" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>physical</span></a> constraints are that apply to them. </p><p>Here we consider both variations of <a href="https://scicomm.xyz/tags/cellSize" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>cellSize</span></a>, using a drug that blocks mitosis without inhibiting growth, and of the interactions with the substrate, by considering the different stages of the quasi-static process of <a href="https://scicomm.xyz/tags/cellSpreading" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>cellSpreading</span></a>, but also by using confinement, and thus presenting more than one substrate for the <a href="https://scicomm.xyz/tags/cell" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>cell</span></a> to spread on. The fibroblasts used in this study present the archetypal shape of a cell spreading on a substrate, with a central cell body which, while flattening, retains a spherical cap shape, and is surrounded by a flat <a href="https://scicomm.xyz/tags/lamella" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>lamella</span></a>. We show that this shape is preserved isometrically between the cell size and cell confinement conditions. Moreover, the length ratio that characterises it establishes early during spreading, at the time when <a href="https://scicomm.xyz/tags/focalAdhesion" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>focalAdhesion</span></a> with the substrate develop. These <a href="https://scicomm.xyz/tags/adhesion" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>adhesion</span></a> patches also collectively follow an isometric scaling with respect to cell spread area, in spite of having individually a shape, size and density which is insensitive to the global cell shape. We show that this isometry follows from the restriction of the distribution of focal adhesions to the flat lamella.</p><p>Since adhesion distribution is crucially important for maintaining the cell shape, we suggest that the observed allometry may be important for the cell to face the <a href="https://scicomm.xyz/tags/mechanical" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>mechanical</span></a> challenges of physiological function.</p>