Intrinsic Curvatures of the Volvox carteri

Extracellular matrix (ECM) is common across living systems and is integral to many cellular processes, as well as a means of providing structure to an organism. The colonial green alga Volvox carteri is one such organism, where ciliated somatic cells produce ECM throughout their lifecycle to generate an expanding spherical colony that is capable of phototaxing through the water column. In these experiments where Volvox carteri is broken into pieces using a homogenizer, we discover that these thin sheets of cells embedded in ECM have an intrinsic curvature different to that of the initial spheroid, and depending on the characteristic shape and size of these broken-off pieces we can infer residual stresses in the ECM of a volvox colony as it expands over its lifecycle. We use confocal imaging techniques to observe how changes in the number of cells, boundary conditions, and age of the tissue changes the final shape of the piece, as well as how the cilia interact and synchronize with each other to propel a piece with a very different shape factor. Using our experimental data as a guide, we then propose a general theoretical framework that recovers these unique shapes and curvatures, and also determines the extent of influence the number of ECM producing neighbours has on the intrinsic curvature of a piece. The sum of this will help answer important questions regarding shape, structural integrity, and aging as it relates to ECM in general.