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科学日报 | 先有鸡还是先有蛋？这个问题现在可能有了答案
Chromosphaera perkinsii is a single-celled species discovered in 2017 in marine sediments around Hawaii. The first signs of its presence on Earth have been dated at over a billion years, well before the appearance of the first animals. A team from the University of Geneva (UNIGE) has observed that this species forms multicellular structures that bear striking similarities to animal embryos. These observations suggest that the genetic programs responsible for embryonic development were already present before the emergence of animal life, or that C. perkinsii evolved independently to develop similar processes. Nature would therefore have possessed the genetic tools to “create eggs” long before it “invented chickens”. This study is published in the journal Nature.
The first life forms to appear on Earth were unicellular, i.e. composed of a single cell, such as yeast or bacteria. Later, animals - multicellular organisms - evolved, developing from a single cell, the egg cell, to form complex beings. This embryonic development follows precise stages that are remarkably similar between animal species and could date back to a period well before the appearance of animals. However, the transition from unicellular species to multicellular organisms is still very poorly understood.
By observing C. perkinsii, the scientists discovered that these cells, once they have reached their maximum size, divide without growing any further, forming multicellular colonies resembling the early stages of animal embryonic development.Unprecedentedly, these colonies persist for around a third of their life cycle and comprise at least two distinct cell types, a surprising phenomenon for this type of organism.
Even more surprisingly, the way these cells divide and the three-dimensional structure they adopt are strikingly reminiscent of the early stages of embryonic development in animals. In collaboration with Dr John Burns (Bigelow Laboratory for Ocean Sciences), analysis of the genetic activity within these colonies revealed intriguing similarities with that observed in animal embryos, suggesting that the genetic programmes governing complex multicellular development were already present over a billion years ago.
This discovery could also shed new light on a long-standing scientific debate concerning 600 million-year-old fossils that resemble embryos, and could challenge certain traditional conceptions of multicellularity.
