The picture shows a 7-cell stage specimen, 6 small cells each containing a nucleus, and the seventh large cell having two nucleuses.
The nuclear structure of the spheroid fossils of the Di'an biota shows that the nucleus has different burial preservation states in different individual specimens.
Image courtesy of respondents
Where are we from? This question has been asked by mankind for thousands of years and is still a mystery to be solved.
The history of the evolution of Earth's life shows that all human and modern complex life, including human beings, is composed of eukaryotic cells. Our ancestors are pointing to single-cell eukaryotes from ancient times billions of years ago. How to effectively identify eukaryotic cells and their subcellular structures in the early fossil record of geological history is the key to reconstructing the early evolution history of eukaryotes.
China's Guizhou Pan'an bio-organic animal embryo fossils are 610 million years old, and it is one of the oldest animal fossil records in the world. Recently, Associate Professor Yin Zongjun and Associate Professor Zhu Maoyan of the Nanjing Institute of Geological Paleontology of the Chinese Academy of Sciences and the international team of partners from the United Kingdom, Brazil and Sweden conducted micro-CT scans of fossils. The results indicate that the larger size of the nuclear subcellular structure in the fossils of the animal embryos of the Chun'an animal is the nucleus, not the artifacts caused by other organelles or secondary rock formation. This will provide important clues and evidence for exploring the evolution of the Earth's early eukaryotic life.
How does the fossil under the micro-CT lens not destroy the internal structure of the fossil three-dimensional reconstruction?
Yin Zongjun was a Ph.D. student at the Nanjing Geological Paleontology Institute of the Chinese Academy of Sciences. The instructor was a famous researcher Zhu Maoyan, one of the main researchers in the fossils of the Pan'an biota in Guizhou.
Yin Zongjun also set his sights on the fossils of the Chun'an biome. It is one of the oldest animal fossil records in the world, and has discovered a series of important fossils such as Guizhou Chunchun. For scientists, finding fossils means that the research is only half done, and it is only after half-finishing the fossil formation process, morphological structure, and role in the evolution of the Earth's life.
The fossils in front of us make scientists somewhat guilty because it is too small. These are the oldest fossils of the earth, the largest of which is less than 2 mm. If you want to successfully complete the research work, the conventional observation method will not work, and you must find another way.
Yin Zongjun thought of a new technology - micro-CT. In Europe at the other end of the globe, a new micro-CT technology is ready to go, with the world's advanced European synchrotron radiation source and Swiss-source sub-micron resolution 3D non-destructive imaging technology.
"The full name of this technology is synchrotron radiation X-ray microtomography, which is essentially a kind of micro-CT technology, but its scanning efficiency and spatial resolution are higher than conventional micro-CT technology. The rate can reach sub-micron level, that is, the micro-scale structure can be clearly observed." Yin Zongjun told reporters that the diameter of human hair is about 80 microns.
After a series of preliminary work such as project design, fossil collection, and application of European synchronous radiation source, Yin Zongjun traveled to Europe with hundreds of specimens of animal embryo fossils. There, researchers used synchrotron radiation X-rays to scan fossils one by one and did a lot of three-dimensional reconstruction experiments.
"The advantage of this technology is that you can observe the three-dimensional appearance of the fossil and all the internal structures without destroying the fossils," Yin Zongjun said.
After scanning, many Eucalyptus embryo fossils, which are equally synchronized and split, and cytoplasmic fossils with similar cell division characteristics preserve abundant subcellular structures. Among them, many large nuclear structures can be seen, which are ellipsoidal or spherical, often developing one in each cell and located in the middle of the cell. Occasionally, it can be seen that the undivided mother cells have two nucleus structures. High-resolution three-dimensional reconstruction found that some well-preserved specimens have a nucleus-like structure with a membrane, and even a more subtle biological structure is developed inside. Experts believe that it is highly likely to be a nucleolus.
Why choose the chloranation method of the Biochemical fossils to preserve the cell structure perfectly?
Europe has such advanced micro-CT scanning technology that scientists all over the world can apply for. Why haven't foreign scientists done similar research in the past?
"Previous people have tried these techniques, but the technology is not enough. Our fossil specimens are another key. The so-called clever woman is difficult to be without the rice. Both the technology and the good fossil materials can solve this problem perfectly." Yin Zongjun said.
Studying the biological structure of fossils at the cytological level has always been the work of paleontologists. However, conventional fossil records preserve only hard-to-destroy hard tissues such as bones. There are very few paleontology studies at the cytological level, because most fossils are not so perfect, and few fossils, especially animal fossils, preserve cytological structures.
The Diane biota is a very rare and specific burial fossil group, because its preserved biological structure is very beautiful, and almost all groups preserve very good cells and subcellular structures.
Yin Zongjun told reporters that the specific buried fossils refer to the type of preservation quality that is different from conventional fossils. Normally, the soft tissue will rot after the death of the organism. Only the hard tissue such as shells and bones will have the opportunity to be preserved as fossils. The specific buried fossils occur under special geological conditions, and the soft body tissues have been preserved and preserved without having to rot or not completely rot. Compared to conventional fossil records, the number of specific buried fossils is small in number and scale.
The Chengjiang biota in Yunnan is a typical Burkins shale-type buried fossil group. A large number of animal soft bodies are preserved here, and even the cardiovascular and vascular systems of the animals can be preserved. Even so, the burial accuracy of Chengjiang fossils did not reach the cell level, and the cellular structure of the soft tissue could not be observed.
Scientists are amazed by the Pan'an biota, where almost all group fossils preserve cell structures and subcellular structures, which are rare in all specific fossilized fossils throughout the geological history. It is a phosphatized three-dimensional storage of a large number of soft tissue of marine micro-eukaryotic multicellular organisms 610 million years ago.
Yin Zongjun said that the preservation of phosphating is also available in other places, but Diane is the oldest and the preservation is also the best. Why is the preservation quality of Chun'an so good, which is also a mystery that has not been completely solved in the field of fossil burial.
Why study new evidence for cell fossils or "jegsaw" for the early evolution of eukaryotic life
Scientists have tried their best to study cell fossils 600 million years ago. What is the intention?
According to experts, all the complex higher life on Earth, including our human beings, consists of eukaryotic cells. Eukaryotic cells are mainly composed of cell membranes, cytoplasm and various organelles. The most obvious difference from prokaryotic cells is that eukaryotic cells have organelles such as the nucleus and prokaryotic cells do not have these complex subcellular structures.
The origin of eukaryotic cells has always been a scientific puzzle. Although many hypotheses have been proposed by scientists, these hypotheses require objective evidence to prove or falsify.
Yin Zongjun said that the reconstruction of the early evolutionary history of eukaryotic life is an important topic. Although there have been many advances, many fossil records of the Precambrian eukaryotic life have been found in the world, but the number of fossils compared to the fossil record of the Phanerozoic. Still too little, the details of preservation are not many, and the biological information that can be provided is relatively limited. Therefore, the early evolutionary history of eukaryotic life is still only a few pieces of sporadic pieces, and many important questions have no clear answer.
Therefore, the Pan'an bio-organized animal fossil is one of the oldest animal fossil records to date, and its subcellular structure has received extensive attention. Among them, the formation of a large-scale nuclear subcellular structure in embryonic fossils is full of controversy.
At first some scholars thought that they might be the nucleus. These fossils are typical eukaryotes, but this explanation has not been widely accepted, so that some people have proposed a new hypothesis that the fossil animal embryos are not animal embryos, but huge. Sulfur oxide bacteria and their aggregates. In 2011, some scholars reinterpreted them as nuclei and claimed to have found evidence of nuclear division. But this explanation has also been opposed by burial studies.
Therefore, the results of Yin Zongjun and others not only prove the "identity" of these nuclear structures, but also show the world that the most important organelles of the nucleus as eukaryotic cells can be preserved very well in the early micro-fossils, and The effective identification of nuclear fossils and the reconstruction of eukaryotic life history provide important clues.
Source: Technology Daily
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