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Team:USTC/Project
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Abstract
It is an amazing process in nature that the evolution from Protozoa to Metazoa. Even in the development of each Metazoa, it is still unknown how the genome regulates the stem cells to develop into different kinds of cells, which can compose different organism, according to where they are in the body. There should be a self-organized procedure. Here we are trying to build a self-organized multiple-cell system based on the quorum sensing system to understand the mechanism of this process. We employed the small molecules in AHL family as the messenger to transmit the orders of differentiation and response and Cre recombinase as the executor of differentiation. Through an artificial designed network, we are trying to construct a new kind of cells, which a cycle composed by GFP will be seen on the plate if the colony is big enough.
Introduction
Background
Self-organization is a process of attraction and repulsion in which the internal organization of a system, usually an open system, increases in complexity without being guided or managed by the outside source. It is a widely observed phenomenon in biology, such as spontaneous folding of proteins and other bio-macromolecules, formation of bilayer lipid membranes, creation of caste by social animals, and so on. Self-organization appears in different levels of living activities, from the formations of macromolecules to the actions of individuals. One of these phenomena that are paid close attention to is pattern formation, which is observed in the development of living organisms and also the evolution from Protozoa to Metazoa. There are two important processes in the pattern formation: differentiation and organization. Many efforts were reported to re-construct the differentiation by designing a specific gene regulation network in E.coli to mimic the differentiation process in multi-cell organisms. Meanwhile, some works have been done to re-build the organization of multi-cell system. A ring formed by GFP has been made on the plate by manually locating together two different types of cells, “sender” cells and “receiver” cells. The two processes are separately achieved in E.coli.
Furthermore, the combination of the two processes to imitate the whole development procedure from a single cell to a self-organized multi-cellular system can enable us to know more about the molecular mechanism of development, and even the evolutionary process. In view of this, our project is focused on how to integrate them together.
Design Gene regulate Network
We design a time-dependent gene regulatory network to construct a self-organized system. The RhlI/RhlR system is employed to report the cell density. The “sender” cell will appear first when the density reaches a certain level. And it will command other cells around it to differentiate into “receiver” cells by sending the signal molecules into the environment. After receiving the signals, the Cre recombinase in “receiver” cells will be generated and scissor the capacity of sending signals. In this way, a spatial differentiation will be accomplished. The “sender” cells are surrounded by the “receiver” cells. The chemical gradient of the signal molecules will be formed sometime after the differentiation process is finished. In this way, the response in a specific region will eventually lead to a picture of green ring in the black background.
It is just the beginning for self-organized graphics in bacteria. Now that the formed ring tells us how the bacteria respond to distance, so in the next step, possibly we can show how the bacteria respond to angle. After that, we can have a better understanding about why we look as what we appear now.
