Using in vivo Optical Sectioning to Investigate Mechanical Aspects of Volvox Development

Abstract

Volvox is a genus of swimming algae consisting of a spherical single sheet of cells. At the end of cell division, embryos form a sphere with their flagella pointing the wrong way (to the inside) and must complete their development by turning themselves inside out. Although this phenomenon was observed hundreds of years ago and has been the subject of extensive study, no quantification of the mechanics has been performed. The simple geometry and connectivity of the cells makes these organisms a tractable example for studying morphogenic processes, while their development still shares features with more complicated mechanisms of gastrulation in animals. Previous study of embryo shapes during inversion required chemical fixation, so that individuals could not be followed through all stages and dynamics were lost. An open-source selective plane illumination microscope (SPIM) [1], has enabled accurate recording of the shapes of embryos as they progress through their inversion process. Unprecedented views of the progress of cell division and the growth of mature spheroids are also within reach. With this dynamic, three-dimensional data, new analysis of embryo and tissue mechanics become possible. [1] Pitrone P. G., Schindelin J., Stuyvenberg L., Preibisch S., Weber M.; Eliceiri K. W., Huisken J., Tomancak P. OpenSPIM: an open access light sheet microscopy platform Nature Methods 10, 598-599 (2013).