A new study from Stanford University researchers reports the motion in the plant nucleus that might explain the stem cell division process.
According to Stanford News, the university's news portal, the study was motivated by a desire to understand how cells divide "in all the right ways to produce healthy tissue." The study was led by postdoctoral scholar Andrew Muroyama, from the lab of Stanford biologist Dominique Bergmann. Observing the flowering plant Arabidopsis thaliana, thale cress, Muroyama reportedly saw the nucleus moving in "unexpected and strangely purposeful ways."
Their findings are published in the journal Current Biology on Thursday, September 17.
Guided Asymmetric Cell Divisions
The published report details how the asymmetrically distributed proteins serve as a "cellular compass" that directs the nucleus in motion. Subsequently, the position of the nucleus influences the patterns taken during stem cell divisions. This process creates minuscule pores throughout the leaf surface, called stomata. These pores, in turn, are responsible for the leaves' ability to balance its carbon dioxide and water levels, making nuclear alignment a point of interest on whether it can affect leaf function later.
With the study conducted in the Bergmann biology lab, the researchers were able to observe plant nuclei motion in the A. thaliana by making them fluorescent under a microscope. The process for asymmetric cell division includes the nucleus moving to one side to allow its daughter cells to have different sizes and face different neighbor cells - with each side playing a different role in determining the leaf pattern in the end.
"I think our research highlights that the ability to watch the behaviors of cellular machines within living organisms can reveal unexpectedly elegant ways that individual cells cooperate to build tissues," Muroyama said. He added that there is still much to learn even in a fundamental process such as cell division.
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Understanding the Mechanics of Stem Cell Division
Professor Bergman, from Stanford's School of Humanities and Sciences and the senior author in the study, described the discovery as "bizarre." He added: "The first move makes sense but the second, in the complete opposite direction, was weird."
It warranted further experiments to allow the researchers to identify if there are other factors at play during stem cell division. While they were already aware of the presence of this cellular compass, they worked towards understanding its mechanisms.
First, they repelled the nucleus before the first division. They observed that this compass created the first set of asymmetric daughter cells. Conversely, by pushing the nucleus immediately after the division, the compass will create another pair of daughters on the other side.
Muroyama explained that the history of the stem cells is critical in understanding the function of their second migration. "The plant doesn't want to generate new stem cells right next to the ones that were just created," he added, further explaining that plants would space these cells. The nucleus is moved after division to "set it up for success" in the second division process.
Additionally, researchers were able to identify a protein that supports the movement of the nucleus. When they disabled this protein, the migration of the nucleus in the second division was prevented and caused less stomata in the resulting leaf.
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