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Study finds cells take out the trash before they divide
Source: | Author:Pekybio | Published time: 2022-05-26 | 37 Views | Share:

Cells may use this strategy to clear out toxic byproducts and give their offspring a clean slate.


MIT researchers have discovered that before cells start to divide, they do a little cleanup, tossing out molecules that they appear not to need anymore.

Using a new method they developed for measuring the dry mass of cells, the researchers found that cells lose about 4 percent of their mass as they enter cell division. The researchers believe that this emptying of trash helps cells to give their offspring a “fresh start,” without the accumulated junk of the parent cell.

“Our hypothesis is that cells might be throwing out things that are building up, toxic components or just things that don’t function properly that you don’t want to have there. It could allow the newborn cells to be born with more functional contents,” says Teemu Miettinen, an MIT research scientist and the lead author of the new study.


Measuring mass

Measuring the dry mass of a cell — the weight of its contents not including the water — is commonly done using a microscopy technique called quantitative phase microscopy. This technique can measure cell growth, but it does not reveal information about the molecular content of the dry mass and it is difficult to use with cells that grow in suspension.

Manalis’ lab has previously developed a technique for measuring the buoyant mass of cells, which is their mass as they float in a fluid such as water. This method measures buoyant mass by flowing cells through a channel embedded in a vibrating cantilever, which can be done repeatedly to track changes in a particular cell’s mass over many hours or days.

For their new study, the researchers wanted to adapt the technique so that it could be used to calculate the dry mass of cells, as well as the density of the dry mass. About 10 years ago, they had discovered that they could calculate a cell’s dry mass if they first measured the cell in normal water and then in heavy water (which contains deuterium instead of ordinary hydrogen). These two measurements can be used to calculate the cell’s dry mass.

However, heavy water is toxic to cells, so they were only able to obtain a single measurement per cell. Last year, Miettinen set out to see if he could design a system in which cells could be measured repeatedly with minimal exposure to heavy water.

In the system he came up with, cells are exposed to heavy water very briefly as they flow through microfluidic channels. It takes only one second for a cell to completely exchange its water content, so the researchers could measure the cell’s mass when it was full of heavy water, compare it to the mass in normal water, and then calculate the dry mass.

The researchers showed that their dry mass measurements qualitatively agreed with previous work using quantitative phase microscopy. And, in addition to providing density of the dry mass, the MIT team’s method enables higher temporal resolution, which proved to be useful for revealing dynamics during mitosis (cell division).


Taking out the trash

In cells undergoing mitosis, the researchers used their new technique to study what happens to cell mass and composition during that process. In a 2019 paper, Miettinen and Manalis found that buoyant mass increases slightly as mitosis begins. However, other studies that used quantitative phase microscopy suggested that cells might retain or lose dry mass early in cell division.

In the new study, the MIT team measured three types of cancer cells, which are easier to study because they divide more frequently than healthy cells. To their surprise, the researchers found that the dry mass of cells actually decreases when they enter the cell division cycle. This mass is regained later on, before division is complete.

Further experiments revealed that as cells enter mitosis, they ramp up activity of a process called lysosomal exocytosis. Lysosomes are cell organelles that break down or recycle cellular waste products, and exocytosis is the process they use to jettison any molecules that aren’t needed any more.