Which came first, the egg or the chicken? This age-old question, which symbolizes the paradox of the origins of life, may have found its answer in the sea depths. An international team led by biochemist Marine Olivetta from the University of Geneva has just shed light on a microscopic organism with a particular functioning. Its mode of reproduction could revolutionize our understanding of embryogenesisthe process of development of an organism, from fertilization of the egg to the formation of the embryo.
THE Chromosphaera perkinsiilurking in the sediments of shallow seas, uses mechanisms strangely similar to those which allow the development of embryos in eggs today, and have been doing so for more than a billion years. This discovery suggests that there ” recipe » genetics of the egg existed long before the egg itself. The results of their work were published on November 6 in the review Nature.
The secrets of ancestral cell division
In the long cycle of evolution, the C. perkinsii occupies a unique position. Belonging to the Ichthyosporean family (a group of eukaryotes close to animals and fungi, but distinct from both), this unicellular organism separated from the lineage that would give rise to animals, more than a billion years ago.
Unlike its parasitic cousins, it leads a free existence in marine sediments. Biochemist Omaya Dudin from the Swiss Federal Institute of Technology underlines the extraordinary nature of this discovery: “ Although unicellular, C. perkinsii already exhibits sophisticated multicellular coordination and differentiation processes, features previously thought to be exclusive to complex organisms like animals. “.
This remarkable capacity thus lays the foundations of a new theory: the mechanisms necessary for the formation of an embryo; and therefore to oviparous reproduction (animals that lay eggs whose embryos develop outside the mother’s body); were already present in the genetic arsenal of life long before the appearance of the first animals. As if nature had developed the instructions even before building the machine.
Amazing embryonic mimicry
The process of reproduction of C. perkinsii bears a striking resemblance to the early stages of embryonic development seen in a fertilized egg. The organism divides by a mechanism called palintomy, rapidly creating several daughter cells without intermediate growth phase. This division results in a hollow structure reminiscent of a microscopic raspberry, similar to the blastula (first stage of embryonic development) that the animal embryo forms in the egg.
Another remarkable fact in C. perkinsii : this cell colony presents at least two types of differentiated cells, maintaining this complex organization for a good part of its life cycle. This early cellular specialization is strikingly reminiscent of the early stages of development of a chicken embryo in its egg. The researchers observed in particular that these cells collaborate in a coordinated manner before dispersing to become independent, thus mimicking the fundamental processes of embryogenesis.
A missing link in the story of life
The discovery of C. perkinsii raises a fundamental question: are we facing the common ancestor who holds the key to the enigma of the egg and the chicken, or is this an example of convergent evolution where nature would have reinvented the same solutions? If this mode of development seems unique among the Ichthyosporeans studied so far, its existence proves that the essential mechanisms necessary for the formation of embryos – and therefore eggs – already existed in the genetic heritage of primitive organisms.
The researchers suggest that: “ C. perkinsii represents a form of transition between temporal and spatial cellular differentiation, providing insight into the evolutionary mechanisms leading to the emergence of animal multicellularity“. In other words, this organism could be the missing link between the simple reproduction of unicellulars and the complex mechanisms of embryonic development that we observe in today’s eggs.
The answer to the chicken-egg riddle could therefore be: neither came firstbut rather the genetic program that would make them possible. The building blocks of embryonic development were already present, but were simply waiting forauspicious moment in evolutionary history to express itself fully in the formation of the first eggs. Additional research on cell differentiation in C. perkinsii will give us additional insight into two essential aspects : the origins of animal multicellularity, but also the deep roots of oviparous reproduction.
- Chromosphaera perkinsiia single-celled marine organism, uses mechanisms similar to those of animal embryos, dating back more than a billion years ago.
- Its mode of cell division is reminiscent of the early stages of embryogenesis, suggesting that the genetic basis of oviparous reproduction existed before the eggs themselves.
- This discovery sheds new light on the evolutionary mechanisms that led to animal multicellularity and the development of eggs.
