Simulated weightlessness swells the nucleus of live human cells in an NYU rotator

A random positioning machine does not cancel gravity. It turns the sample, rotating the dish along two independent axes on a path the researchers describe as simulated microgravity, weightlessness produced on Earth, using the same principle as the larger devices astronauts train in ^[8]. The rotation has a side effect: liquid in the dish moves across the cells, and in true zero gravity those flows are absent ^[9].

So the NYU group wrote rotational algorithms that hold the flows down, plus a second set designed to drive flows and measure what they do to the cell and the genome ^[9][10]. They also prepared dishes free of air bubbles, which interfere with the measurements ^[7]. Together the changes cut both the flows and the cell aggregates that, by the team's account, obscured simulated microgravity effects in earlier work ^[11].

After 24 hours of exposure, cells in the strong-flow arm were elongated while cells under simulated microgravity kept their shape ^[15]. Nuclear volume moved the other way: it increased under simulated weightlessness, which the researchers take as evidence that gravity keeps the nucleus smaller ^[16]. The flow arm is what makes that reading available. One condition against an untouched control would have left shear as the obvious rival explanation for anything that changed.

Zidovska, who led the study and is an associate professor in NYU's physics department, said gravity "is a constant mechanical stress on everything" ^[2][21]. On the design: "To uncover it, you have to remove gravity as a force, so we simulated zero gravity in our experiments," she said ^[3].

The packing problem the study pokes at is severe. Two meters of DNA sits inside a nucleus barely 10 micrometers across, about the width of a silk fiber ^[17], a length ratio of roughly 200,000 to one ^[20]. Departures from that organization are linked to cancer and developmental disease, and the physical principles that maintain it are not well understood ^[18][19].

The exposure was a single 24-hour window in cultured cells, and the analysis tracked cell shape and volume, nuclear shape and volume, the nuclear envelope, the genome, and the nucleolus ^[13]. DNA damage under simulated microgravity was among the things examined ^[14]; the account of the results does not state what that analysis found.

The paper is in Science Advances ^[1], and the spaceflight claim attached to it is a hope: "We think our findings can be useful in better understanding how space travel affects us," Zidovska said ^[4]. Every cell in this design stayed on Earth. I would carry the nuclear volume result forward on the strength of the flow comparison, and treat the orbital extrapolation as open until someone runs the same imaging above the atmosphere. For Earth-bound work the implication is narrower and more immediate: if steady 1 g load sets nuclear volume, then every culture dish carries a mechanical input that stays fixed. "We do not know if or how the presence of gravity affects this organization and if the absence of gravity would cause genomic aberrations," Zidovska said ^[5].