Active mechanism locks in the size of a cell's nucleus

December 24, 2007

Cells know that size matters, especially when it comes to the nucleus. In the early 1900s, German scientists first proposed that the size of a nucleus is always proportional to the size of its cell. Now, more than a century later, researchers at Rockefeller University show that an active mechanism controls this process. This mechanism, however, doesn’t reside within the nucleus as many once thought, but instead comes from the cell’s cytoplasm.

In a series of experiments, coauthor Frank Neumann, together with Paul Nurse, head of the Laboratory of Yeast Genetics and Cell Biology, found that regardless of the size or shape of fission yeast, the volume of its nucleus hovers around eight percent — a volume that not only remains constant throughout development, but also resists change, in a wide range of experimental and natural conditions. These findings, which appear in the November 19 issue of the Journal of Cell Biology, raise the question of why cells keep such close tabs on the size and shape of their nuclei.

To test whether the amount of DNA influences the nucleus’s size, Neumann and Nurse genetically manipulated the fission yeast so that the amount of DNA within the nucleus doubled with each cell cycle without the nucleus ever dividing. Nuclei with as much as 32 times more DNA than other nuclei maintained the same nucleus-to-cell ratio, a finding that dispelled the theory that it is the amount of DNA and how tightly it is packed that determines the nucleus’s size. “This was perhaps our most surprising finding,” says Neumann, “that DNA is not what is measured to determine nuclear size.” The researchers also found that fission yeast do not measure cell length to lock in this nucleus-to-cell ratio.

Rather, Neumann and Nurse show that it’s what’s outside the nucleus — not inside it — that determines the size of the nucleus. This time, they confirmed this finding not by doubling the amount of DNA within the nucleus, but the number of nuclei within the fission yeast — single-cell organisms that look like long, straight rods. In this experiment, each cell had four unevenly distributed nuclei.

During cell growth, the volume of each nucleus became directly proportional to the amount of “surrounding” cytoplasm. Particularly, the two nuclei at the ends of the rods, which were surrounded by relatively more cytoplasm, grew faster than the two nuclei between them. When Neumann and Nurse repositioned nuclei to areas with relatively more cytoplasm, the previously small nuclei grew faster than the others until the proper ratio was achieved.

The researchers saw the same results when they genetically modified the multi-nucleated cells to sprout an arm. The nuclei that were close to this junction increased in size since the relative amount of cytoplasm had now increased. Taken together, these experiments suggest that components within the cytoplasm, not DNA content of the nucleus, play an important role in nuclear size control.

When Neumann and Nurse modified the fission yeast cells such that nuclei occupied two times more of the cell volume, the nuclei didn’t shrink but “waited” until the cell became sufficiently large before they started to grow.

Likewise, a nucleus that occupied less than eight percent of the cell’s volume grew faster than it would have had its nucleus-to-cell ratio not been modified, suggesting that nuclear growth is not directly coupled to cell growth; rather, the nucleus can sense changes to the ratio and adjust its growth accordingly. “These findings provide the first hint of a mechanism and are the basis of uncovering the molecular mechanism of how a cell senses its nucleus’s size,” says Neumann.

Citation: Journal of Cell Biology 179(4): 593–600 (November 2007)

Source: Rockefeller University

Explore further: Label-free technique that images DNA in vivo

Related Stories

Label-free technique that images DNA in vivo

September 9, 2015

(—A group of researchers from Harvard University report being able to observe DNA dynamics during cell division in vivo using time-lapse stimulated Raman scattering microscopy and without using fluorescent labels. ...

Researchers develop fast test for invasive carp

August 11, 2015

A Case Western Reserve University graduate student turned a research paper into a field test that quickly determines whether an Asian carp invading Lake Erie is sterile or can reproduce.

Recommended for you

Most EU nations seek to bar GM crops

October 4, 2015

Nineteen of the 28 EU member states have applied to keep genetically modified crops out of all or part of their territory, the bloc's executive arm said Sunday, the deadline for opting out of new European legislation on GM ...

The dark side of Nobel prizewinning research

October 4, 2015

Think of the Nobel prizes and you think of groundbreaking research bettering mankind, but the awards have also honoured some quite unhumanitarian inventions such as chemical weapons, DDT and lobotomies.

Internet giants race to faster mobile news apps

October 4, 2015

US tech giants are turning to the news in their competition for mobile users, developing new, faster ways to deliver content, but the benefits for struggling media outlets remain unclear.

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.