Team:iHKU/Project

Overview
Pattern formation is one of the most common yet fascinating biological phenomena happening in our daily lives, though for centuries, biologists, physicists and mathematicians have struggled to understand its nature. How do highly ordered patterns arise from a few living cells? How can our hands, our eyes, our bones form their shape with such an extremely low mistake rate? This question is fascinating but crucial. There are many possible way to form highly complicated patterns. Controlled cell movement is one possible way. Our group is now focusing on pattern formation through cell motility control. The aim of our project is to generate a simple pattern, a set of concentric circles based on a strain of E. coli that we created. We also aim to model the pattern formation by controlled cell movement.

Bacteria use their flagella to move around. To generate a recognizable and stable pattern, bacterial movement must be controlled and coordinated. This can be accomplished by designing a genetic circuits coupling bacterial quorum sensing system and genes controlling mobility. There are several key genes responsible for the movement of flagella, two of them are cheY and cheZ. CheY protein has two forms: its phosphorylated form makes flagella rotate clockwise and the cell will tumble; its dephosphorylated form makes flagella rotate counterclockwise and the cell will be driven straight in one direction (run). CheZ protein can help the progress of dephosphorylation of protein cheY. By controlling the expression of cheZ we can control the cell movement. We have generated MG3, a strain in which gene cheZ is knocked out from its genome. Plasmids containing gene cheZ with engineered promoters will response to the quorum sensing signals according to local cell density, and gene cheZ is either activated or inhibited consequently. The cell will “run” away from or stay in one place using cell density as a cue. Thus by controlling the initial cell density and growth conditions, andthe quorum sensing between cells, we canl lead them to form different patterns.

Project Details

 * In the beginning we managed control the motility of the cell by knocking out the cheZ, a gene responsible for the regulation of cell motility, we generated a cell strain liable for motility regulation--MG3.
 * In order to generate coordinated cell movement according to the location of cells, we design a genetic circuit to place the cheZ at the downstream of an artificial quorum sensing system.
 * We have synthesized the circuit part by part. Firstly the quorum sensing part of luxR, luxRI2 and plux, then the motility part of cheZ. After testing and calibrating the two part separately by reporter gene assay and migration test, we coupled the two parts in MG3.
 * The engineered MG3 cells were inoculated onto Agar plates to observe the pattern formed. So far we are able to generate different forms of concentric cycles on the Agar plate by varying the initial inoculation condition. We are now trying to generate different patterns such as Olympic rings by fine tuning the genetic circuits and and environmental factors. At the same time, we are building a math model and trying to understand the patterns formed.