WIKIMEDIA, EKEMIt has long been believed that cells with diameters much bigger than 10 microns—the typical size of most eukaryotic cells—are rare because it is difficult for larger cells to acquire nutrients or expel waste. The oocytes of most animals are much bigger, and they likewise have larger nuclei, which often contain high concentrations of the protein actin. Cell biologists Marina Feric and Clifford Brangwynne of Princeton University in New Jersey have shown that cells are likely small because of gravitational forces and that the extra actin in oocyte nuclei stabilizes the responses of larger cells to gravity. Their work, published in the October issue of Nature Cell Biology, was surprising because cell biologists “really have never, in my experience, worried about gravity—or thought about it,” Brangwynne told The Atlantic.

Brangwynne and Feric injected tiny plastic beads into the germinal vesicles—nuclei—of 1 millimeter oocytes from...