Which came first – the chicken or the egg?
All animals begin development from a single-celled zygote and progress through a series of coordinated steps to become complex multicellular organisms. While the fundamental processes of early embryogenesis are highly conserved across animals, the evolutionary origins of how and when this developmental process first evolved are still unclear.
Omaya Dudin, recently appointed as an assistant professor at the Department of Biochemistry at the UNIGE Faculty of Science and formerly an SNSF Ambizione researcher at EPFL, leads a research team focused on Chromosphaera Perkins (C. Perkins), an ancient protist species.
This unicellular organism, which diverged from the animal evolutionary lineage over a billion years ago, provides important insights into the mechanisms that may have contributed to the transition from unicellularity to multicellularity.
Scientists investigated how multicellular life evolves from scratch
These observations imply that the genetic programs responsible for embryonic development may have existed before the emergence of animals or that C. perkinsii independently evolved similar developmental processes. In this sense, nature may have had the genetic tools to “create eggs” long before it “invented chickens.”
Chromosphaera Perkins, or C. Perkins, is an ancestral species of protist. Diverging from the animal evolutionary line over a billion years ago, it provides valuable insights into the mechanisms that may have driven the transition to multicellularity.
Observations revealed that once these cells reach their maximum size, they divide without growing further, forming multicellular colonies that resemble the early stages of animal embryonic development. Remarkably, these colonies persist for about a third of their life cycle and consist of at least two distinct cell types, a surprising feature for this unicellular organism.
Early embryonic development studied in new and innovative ways
Omaya Dudin, who led this research, said, “Although C. perkinsii is a unicellular species, this behavior shows that multicellular coordination and differentiation processes are already present in the species well before the first animals appeared on Earth.”
Even more surprisingly, the way C. perkinsii cells divide and the three-dimensional structures they form closely resemble the early stages of embryonic development in animals. In collaboration with Dr. John Burns from the Bigelow Laboratory for Ocean Sciences, the team analyzed the genetic activity within these colonies, revealing striking similarities to the genetic programs observed in animal embryos. This suggests that the genetic frameworks for complex multicellular development may have existed over a billion years ago.
Marine Olivetta, a laboratory technician at the UNIGE Faculty of Science and the study’s first author, remarked, “It’s fascinating. A species discovered very recently allows us to go back in time more than a billion years.”
The study indicates that the principles of embryonic development predate animals, or that mechanisms for multicellular development evolved independently in *C. perkinsii*.
Journal Reference:
- Olivetta, M., Bhickta, C., Chiaruttini, N. et al. A multicellular developmental program in a close animal relative. Nature 635, 382–389 (2024). DOI: 10.1038/s41586-024-08115-3