Cells in our body are constantly dividing. With each division, the genetic information contained in the chromosomes is doubled and each daughter cell receives a complete copy of the genetic material. It is a demanding process, a clockwork This involves sophisticated and rapid changes within the cell. To make this possible, the cell has microtubules, tiny tube-shaped structures. It’s been a long time since we tried to understand how they come about. ,
Now, for the first time, a team from the Center for Genomic Regulation (CRG), the National Cancer Research Center (CNIO) and the Higher Council for Scientific Research (IBMB-CSIC) have managed to create a film that shows how this is done Human cells begin to form their microtubules.
The results published today on-line in the magazine Sciencesolve a problem raised years ago, laying the foundation for future advances in the treatment of diseases ranging from cancer to neurodevelopmental disorders.
“Ropes” that help divide chromosomes
Oscar Llorca, director of the structural biology program at CNIO and lead co-author of the paper, describes what happens in the cell when cell division begins: “Once the chromosomes have duplicated the genetic information, they are placed in the middle of the cell and. This exceptionally quickly creates large tubes at its two ends that hook the chromosomes and pull each of the copies to the two poles of the cell. Only then is it possible encapsulate a copy of all of our genetic material in every daughter cell.
Microtubules play a key role in cell division. We need to understand very well the mechanisms that trigger the formation of these microtubules in the right place and at the right time.
The structures that come into being, “like long ropes that reach the chromosomes to divide them,” explains Llorca, are the microtubules. “That’s why we say that microtubules play a key role in cell division. “We need to understand very well the mechanisms that trigger the formation of these microtubules in the right place and at the right time.”
Microtubules are tubes measuring thousandths of a millimeter long and nanometers (millionths of a millimeter) in diameter. Not only do they play a crucial role in cell division, but they also act as highways for the transport of cell components between different cell areas. Among other things, they are also structural elements that give the cell its shape. A good understanding of their training has implications for several areas of biomedicine.
“Microtubules are crucial components of cells. Here we record how their formation process takes place in human cells. Given the fundamental role of microtubules in cell biology, this could lead to new therapeutic approaches for a variety of diseases in the future,” explains ICREA research professor Thomas SurreyCRG researcher and lead co-author of the article in Science.
The importance of these structures in cell biology could lead to new therapeutic approaches for a variety of diseases in the future.
a molecular ring
The high-definition pictures Now they get an answer to a question that has been posed for years: How does the formation of microtubules begin in the first stages of cell division?
Now we know that everything starts when it closes and forms a ring, a complex structure called several proteins gTuRC (pronounced “gammaturc”).
The shape of gTuRC, its three-dimensional structure, was discovered several years ago and surprised researchers. It was expected to be a closed ring that serves as the basic template for building the microtubules, but these proteins They looked like an open washing machine. Its dimensions and shape were incompatible with those of a microtubule template.
The new work from CRG and CNIO reveals the mechanism by which gTuRC closes into a ring, effectively becoming a perfect template that can initiate microtubule formation. Its closure occurs when the first molecular piece of a microtubule attaches.
“That’s him Trick that uses the cell to close gTuRC“, explains Llorca. “Once that first stone enters, an area of this mechanism can hook it and act as a loop like a fitting that pulls the ring until it closes and starts the process.”
To visualize this process, it was necessary to purify gTuRC from human cells and reproduce the microtubule initiation process in the test tube. The samples were also observed Electron cryomicroscopes and artificial intelligence was used in data analysis.
a million images
One of the challenges was the high speed of the microtubule assembly process. The CRG group managed to slow it down in the laboratory and also stop the growth of microtubules in order to be able to analyze the early stages of the process.
“We needed to find conditions that would allow us to image more than a million nucleating microtubules before they grew too large and obscured the action of γ-TuRC. We achieved this by using molecular techniques from our laboratory and then freezing the microtubule samples. ” explained Claudia BritoPostdoctoral researcher at the CRG and first author of the study.
Microtubules under construction were observed on the IBMB-CSIC Electron Cryomics Platform at the Joint Electron Microscopy Center (JEMCA) in the ALBA synchrotron.
“They were frozen in a thin layer of ice, preserving the natural shape of the molecules involved,” he explains. Pablo Guerra, responsible for this platform. In this way, the best experimental conditions for observing microtubule formation were determined.
The best frozen samples were sent and transferred to BREM (Basque Resource for Electron Microscopy) for imaging Marina Serna and Oscar Llorca from CNIO for their analysis and determination of three-dimensional structures at atomic resolution.
Artificial intelligence for assembly
In practice, more than a million microtubules in different growth phases is equivalent to many images of a high-resolution film. You “just” have to order them correctly to see the film. This work fell to the CNIO team, which completed it using artificial intelligence techniques.
“Determining the three-dimensional structure of growing microtubules from microscope images was extremely complex. We needed several tools digital image processing“explains Marina Serna, CNIO researcher.
For Llorca, “the big challenge was to analyze high-resolution images of a dynamic process in which we observed several phases at the same time.” This was made possible by the use of neural networks that allowed us to organize all this complexity.”
The results are three-dimensional structures at atomic resolution that depict the different stages at which microtubule assembly begins and how the γ-TuRC ring becomes the template that initiates microtubule formation.
Health effects
Llorca explains: “This finding is relevant because we looked at a very basic mechanism of cell division that we did not know how it worked in humans.”
It is a useful foundational knowledge for learning how to correct errors in microtubule function that are linked to cancer, neurodevelopmental disorders, and other conditions from breathing problems to heart disease.
“Some of the drugs used today to treat cancer prevent the formation or dynamics of microtubules,” says Llorca. “However, these drugs affect microtubules indiscriminately, both in cancer cells and healthy cells, leading to side effects.” A detailed knowledge of how microtubules are formed can help develop more targeted treatments that affect microtubule formation and Enabling advances in the treatment of cancer and other diseases.”
Next step: understand the regulation
For his part, Thomas Surrey explains the next steps in understanding microtubules, which involve understanding how their formation is regulated: “The nucleation process determines where and how many microtubules are located in a cell. The conformational changes we observed are likely controlled by yet-to-be-discovered regulators in cells. Several candidates have been described in other studies, but their mechanism of action is not clear.”
Future work “will clarify how the regulators bind to γ-TuRC and how they influence it.” Conformational changes during nucleation“could transform our understanding of how microtubules work and, over time, provide alternative sites that one might want to target to prevent cancer cells from progressing through the cell cycle,” Surrey concludes.
The work carried out in the Surrey laboratory was supported by the Spanish Ministry of Science and Innovation, the EMBL Association, the Severo Ochoa Center of Excellence and the CERCA program of the Generalitat of Catalonia, as well as the Francis Crick Institute.
