Study finds cells take out the trash before they divide

Amazing stuff! However, I have a hunch that this dry mass approach has its own problems and may produce artifacts or overlooks other aspects of the process. 

And perhaps cells are not simply taking out trash as the title suggests. Perhaps, there is much more behind this!

"... 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. ...
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. .."

From the abstract:

"Cell mass and composition change with cell cycle progression. Our previous work characterized buoyant mass dynamics in mitosis (Miettinen et al., 2019), but how dry mass and cell composition change in mitosis has remained unclear. To better understand mitotic cell growth and compositional changes, we develop a single-cell approach for monitoring dry mass and the density of that dry mass every ~75 s with 1.3% and 0.3% measurement precision, respectively. We find that suspension grown mammalian cells lose dry mass and increase dry mass density following mitotic entry. These changes display large, non-genetic cell-to-cell variability, and the changes are reversed at metaphase-anaphase transition, after which dry mass continues accumulating. The change in dry mass density causes buoyant and dry mass to differ specifically in early mitosis, thus reconciling existing literature on mitotic cell growth. Mechanistically, cells in early mitosis increase lysosomal exocytosis, and inhibition of lysosomal exocytosis decreases the dry mass loss and dry mass density increase in mitosis. ... reveals that mitosis is coupled to extensive exocytosis-mediated secretion of cellular contents."

Study finds cells take out the trash before they divide | MIT News | Massachusetts Institute of Technology Cells may use this strategy to clear out toxic byproducts and give their offspring a clean slate.

Single-cell monitoring of dry mass and dry mass density reveals exocytosis of cellular dry contents in mitosis (open access)