In 2017, scientists discovered Chromosphaera perkinsii, a single-celled protist species found in marine sediments near Hawaii. This ancient organism dates back more than a billion years, well before the appearance of the first animals. Research led by a team at the University of Geneva (UNIGE) has now revealed that C. perkinsii forms multicellular structures remarkably similar to the embryonic stages of animals. These findings, published in the journal Nature, suggest that the genetic foundations for complex development may have existed far earlier than previously thought or, alternatively, that C. perkinsii evolved its own unique methods of organizing cells in a multicellular structure.
Life on Earth began with single-celled organisms like bacteria and yeast. The transition to multicellular organisms—complex life forms such as animals—marked a significant evolutionary leap, with individual cells working together to form a single entity. This transformation involved precise developmental stages that all animals undergo, beginning with a single egg cell that divides and differentiates into a complex organism. Understanding this transition remains one of the great mysteries of evolutionary biology.
At UNIGE, Omaya Dudin, an assistant professor in the Department of Biochemistry, and his team focused on Chromosphaera perkinsii, which separated from the animal lineage over a billion years ago. The organism provides valuable insights into how multicellular structures may have originated. Dudin’s research found that C. perkinsii cells, after reaching a maximum size, divide into multiple cells that remain together, forming colonies with distinct cell types that resemble the earliest stages of embryonic development in animals.
These colonies persist for about one-third of the organism’s life cycle, an unexpected behavior for a unicellular species. Typically, single-celled organisms divide and separate, yet C. perkinsii forms tightly connected multicellular structures. These colonies also show evidence of at least two differentiated cell types, a feature rarely seen in such simple life forms. According to Dudin, this behavior suggests that processes for coordinating and differentiating cells existed well before the first animals evolved.
More surprising still is that the structure of these colonies closely resembles the three-dimensional organization seen in animal embryos. Collaborating with Dr. John Burns from the Bigelow Laboratory for Ocean Sciences, the team analyzed the genetic activity within these multicellular colonies. They found parallels between the gene activity in C. perkinsii colonies and that observed in early-stage animal embryos. This discovery suggests that genetic programs necessary for complex development could have existed over a billion years ago, long before animals.
Marine Olivetta, a laboratory technician at UNIGE and the first author of the study, expressed her fascination with this ancient organism’s behavior, noting how it allows scientists to glimpse a billion years into the past. The findings suggest that either embryonic development mechanisms predated animals or that multicellular development arose independently in C. perkinsii.
This research could also have implications for interpreting ancient fossils, some of which resemble embryos and date back around 600 million years. Traditionally, such fossils have been considered evidence of early animals, but C. perkinsii complicates this view, as it shows that embryo-like structures can arise in non-animal organisms. This discovery may challenge longstanding ideas about how multicellularity evolved, offering new perspectives on the origins and diversification of life on Earth.
Source: University of Geneva