New technology tracks how a single cell produces a complete body.

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 New technology tracks how a single cell produces a complete body.


My first reaction was, Wow! RobertZinzen, a developmental biologist at the Institute of medical systems biology, Berlin, Germany. Not long ago, two other papers, published online in the journal Science, traced the cell gene activity of a simple flat worm, a cell that was regenerated after being cut into a small piece. However, Zinzen said that for vertebrates, complexity is much higher. However, researchers have successfully traced the emergence of thousands of cells and their descendants. I think the future of developmental biology will be conventional single cell sequencing of embryos. DetlevArendt, an evolutionary developmental biologist at the European Molecular Biology Laboratory in Heidelberg, said. All these studies begin by slowly dissolving the different stages of the embryo in a specific solution, then sloshing or stirring them until a free single cell appears. For each cell, the researchers then determine the sequence of all messenger RNA (mRNA) chains. MRNA reflects the transcribed gene. At the Harvard University, the team led by AllonKlein, MarcKirschner and SeanMegason focuses on two kinds of vertebrates, zebrafish and frogs that have been studied for decades by developmental biologists. In one study, Klein and Megason analyzed about 92 thousand zebrafish cells and collected mRNA data from 7 different embryonic stages. The team started with 4 hours of embryo formation and sequenced at 24 hours after the embryo was fertilized. At this point, the most basic organs have begun to appear. The gene activity pattern of each cell reveals its developmental path and its final identity. To track how cells and their offspring have changed over time, researchers have installed a gene tracer on some single cell zebra fish embryos: a number of unique tiny DNA fragments injected into the cytoplasm of the embryo. As cells continue to divide in growing embryos, these barcodes locate the pathway into the nucleus and are incorporated into the cytoplasm. By the end of the experiment, each cell lineage eventually had a unique bar code combination. By integrating this information with genetic activity, the team can track the cells fate in real time in order to determine how the fertilized egg produces a variety of differentiated cells, such as the heart, nerves and skin. In another independent study, a team led by AlexanderSchier, a developmental biologist at the Harvard University, created its own calculation to track the cells of the growing zebrafish. After 9 hours of early embryo growth, the team sampled the cells every 45 minutes and sequenced the mRNA of these cells. The software reconstructs the biography of each cell by obtaining the gene activity of the completely differentiated cells and analyzing which cells have the most similar gene activity. The system can deduce each embryo stage backwards until the undifferentiated cells begin. Schier indicated that the reconstructed results showed that the initial single cell embryos produced 25 main cell types. This analysis has caused some shock. Developmental biologists once believed that once the cells moved toward a path like muscle cells, no deviation would occur. However, Schier and colleagues reported that changes in gene activity indicate that some zebrafish cells are turning halfway and forming different types. The whole picture is much more complicated than we think. Megason says. For the tropical Xenopus (one kind of frog), Kirschner and Klein sequenced single cell RNA for 10 different stages of the embryo after fertilization for 5~22 hours. The team finally read the mRNA of 137 thousand cells. Gene activity data show that even when frog embryos appear to be undifferentiated, their cells begin to show their final identity. When Klein, Kirschner and Megason compared the findings of frogs and zebrafish, they found startling differences. For example, the developmental pathways of specific cell types vary greatly due to species differences. At the same time, although the activity of key transcription factor genes is similar in common cell types, the activity of other genes in some cell types is far beyond the differences between the two species considered by the researchers. Such studies may also provide recipes for stem cell scientists and tissue engineers who want to create new cell types. DavidKimelman, a developmental biologist at the University of Washington, believes that the latest results are a great effort and a feat in understanding the most fundamental problems in the field of developmental biology. (Zong Hua) the source of this article: editor of science net: Guo Hao _NT5629 When Klein, Kirschner and Megason compared the findings of frogs and zebrafish, they found startling differences. For example, the developmental pathways of specific cell types vary greatly due to species differences. At the same time, although the activity of key transcription factor genes is similar in common cell types, the activity of other genes in some cell types is far beyond the differences between the two species considered by the researchers. Such studies may also provide recipes for stem cell scientists and tissue engineers who want to create new cell types. DavidKimelman, a developmental biologist at the University of Washington, believes that the latest results are a great effort and a feat in understanding the most fundamental problems in the field of developmental biology. (Zong Hua)