The Question
The transition from single-celled to multicellular organisms marks a pivotal moment in the evolution of life on Earth. It has been suggested that this transition may have begun when single-celled organisms failed to undergo complete division, resulting in daughter cells that remained interconnected through their cytoplasm. Notably, multicellular organisms initiate their development with a fertilized egg that undergoes a series of rapid cell divisions, which in some species are incomplete. This process bears a striking resemblance to the proposed mechanisms that led to the emergence of multicellularity. However, it remains unclear how these incomplete divisions can produce cells with distinct forms and functions — an essential characteristic of multicellular organisms.
The Approach
To address this question, the project Cytoplasmic Self-Organization in Early Animal Development will investigate how cells acquire distinct forms and functions in embryos undergoing either complete divisions (ascidians — the closest invertebrate relatives of vertebrates) or incomplete divisions (zebrafish — a popular vertebrate model organism) at the onset of their development.
The researchers’ initial observations suggest an intriguing possibility: In embryos with incomplete divisions, the cytoplasm can self-organize into cell-like compartments that exhibit characteristics typical of intact cells. This implies that the formation and differentiation of cells in multicellular organisms may be driven by this self-organizing property of the cytoplasm rather than solely by the mechanisms of cell division. This hypothesis will be tested through experiments that modify the extent of cell division in both zebrafish and ascidian embryos, exploring whether and how cytoplasmic self-organization can compensate for the lack of division in these scenarios.
The project is being led by Carl-Philipp Heisenberg at the Institute of Science and Technology Austria (ISTA).
Feature image: Nuclei visible via DAPI staining (Photo: Heisenberg lab).
