The injection procedure involves a needle that damages the cell, so it is unclear if the measured properties are representative of a healthy, undisturbed cell, Zidovska says. Previous measurements of nuclear properties have used small beads, which are injected into the nucleus and then observed while being manipulated by magnetic fields. “These vital cellular processes will be impacted by the material properties inside the nucleus,” says Alexandra Zidovska, of New York University. The machinery produces messenger RNA strands that travel from the nucleus to the protein manufacturing sites called ribosomes. Most cells other than bacteria have a nucleus that hosts the organism’s DNA along with the complex machinery for reading the genetic code in an organized way. The team used micrometer-sized cellular structures, called nucleoli, to act as natural probes of the nuclear environment and found that the viscosity was about 300 times that of honey, in agreement with other more invasive measurements. Now researchers have developed the first noninvasive technique for measuring the viscosity inside the nucleus. Understanding how these molecules operate requires an understanding of the medium through which they move. The cell nucleus is the headquarters for many molecules, such as proteins and RNA, that carry information throughout the cell. By tracking this fusion over time, researchers can measure the viscosity inside the nucleus. A pair of nucleoli (red) inside a cell nucleus (green) move toward fusion in this series of chronological images.

Small bead viscosity test