Fig. 1

Asexual development of Volvox carteri, wild-type phenotype and separation of cell types. a Asexual development of V. carteri [8, 35]. Volvox algae exist as distinct males and females. However, during asexual development the males look just like the females (for sexual development see Additional file 1: Figure S1). During embryogenesis, mature asexual reproductive cells (gonidia) undergo a rapid series of 11–12 cleavage divisions, some of which are asymmetric. The fully cleaved embryo contains all of the cells of both types that will be present in an adult but it is inside out with respect to the adult configuration. This awkward condition is quickly corrected by a gastrulation-like inversion process [144]. Then, both the adult spheroid and the juvenile spheroids within it expand by the deposition of the extracellular matrix (ECM). The juveniles eventually hatch from their parent spheroid and the somatic cells of the parent undergo senescence and die, while the reproductive cells of the juvenile spheroids mature. Under standard conditions [117, 133, 134], the asexual life-cycle takes 48 h. For clarity, each parent spheroid in this figure contains only 4 of the ~16 reproductive cells, embryos, or descendant spheroids. b Wild-type phenotype of an asexual female of V. carteri containing approximately 2000 small, terminally differentiated, biflagellate somatic cells at the surface and approximately 16 large reproductive cells in the interior. The reproductive cells are at the developmental stage just before the beginning of embryogenesis. More than 95% of the volume of such a spheroid consists of a complex but transparent ECM. c Mechanical separation of the cell types of three biological replicates was performed at the developmental stage just before the onset of cell cleavage of reproductive cells. The separated cell types were then used for the RNA-Seq analysis. d Isolated somatic cell sheets. e Isolated reproductive cells