A cellular GPS system regulates cell division in bacteria
Almost all cells undergo cell division. Cell division is highly regulated to make sure that cells divide at the right place and at the right time. So, again and again, cells are faced with the formidable challenge of having to identify the correct place and time to divide. Bacteria typically divide in the middle to generate two daughters of equal size and shape and each containing one chromosome. However, for most bacteria, it is not known how they identify their middle.
A case in point is the bacterium Myxococcus xanthus. M. xanthus cells are rod-shaped and they divide precisely in the middle every 5 hours. To begin to understand how these cells find their middle, Dominik Schumacher and Lotte Søgaard-Andersen, two of the lead authors on the paper, focused on three proteins called PomX, PomY and PomZ. “We knew that when cells were missing PomZ, cell division went awry but we did not know why” explains Dominik Schumacher. “By carefully comparing the genes of bacteria that are closely related to M. xanthus, we found that two genes that are right next to the pomZ gene are conserved in a number of these bacteria. So, we thought that maybe these two proteins could work together with PomZ” Dominik Schumacher explains. This idea turned out to be correct. In the paper published in Developmental Cell, Dominik Schumacher and colleagues went on to show that these two genes code for two proteins, PomX and PomY, and that they function together with PomZ.
Movement of the PomXYZ complex from a cell division site and up to the midpoint of the two daughter cells. The complex was visualized by fusion of a fluorescent protein to PomX.
The scientists could also show that the three PomXYZ proteins form a large complex that translocate across the chromosome in a biased random walk until it reaches the middle of the chromosome. Once the complex has reached the middle of the chromosome, it remains at that position. Because the middle of the chromosome is precisely in the middle of the cell, the Pom complex is eventually positioned correctly at midcell where it then stimulates cell division.
To understand the PomXYZ complex navigates its way precisely to midcell, the Marburg scientists teamed up with Erwin Frey, a theoretical physicist at the Ludwig-Maximilian University in Munich, and Silke Bergeler, a doctoral researcher in Erwin Frey’s research group. By combining the computational modeling and simulations in the Frey group with the experimental work, the scientists were able to propose a model for how the PomXYZ complex functions as a cellular GPS system and surfs across the chromosome to end up precisely at midcell.
Bacteria have evolved different systems to make sure that they divide at the correct place and time. In future studies, the scientists wants to analyze the selective pressure that favors these different systems in different bacteria.
This study was funded by the Deutsche Forschungsgemeinschaft (DFG) within the framework of the Transregio 174 “Spatiotemporal dynamics of bacterial cells”, the Max Planck Society and the Graduate School of Quantitative Biosciences, Munich.
Reference:
Schumacher, D., Bergeler, S., Harms, A., Vonck, J., Huneke-Voigt, S., Frey, E. & Søgaard-Andersen, L. (2017) The PomXYZ proteins self-organize on the bacterial nucleoid to stimulate cell division. Developmental Cell 41, 299-314.
