Image of the Day: Scrambled Frog Eggs

Cellular innards can reorganize themselves to form structures similar to cells.

Emily Makowski
Nov 6, 2019
Xenopus eggs mixed with varying sperm concentrations
Cheng et al.

When Xenopus frog eggs are experimentally ruptured, their cytoplasm rearranges itself to form compartments similar to cells, according to a study published October 31 in Science. The researchers, led by James Ferrell, a systems biologist at Stanford University, found that the reorganization occurred with or without the addition of sperm nuclei, suggesting that the mechanism is inherent in the eggs.

“If you take the cytoplasm of the frog egg—note that the cytoplasm has been homogenized, so whatever spatial structure that was there has been completely disrupted—and just let it sit at room temperature, it will reorganize itself and form small cell-like units. That’s pretty amazing,” says Xianrui Cheng, a postdoc in Ferrell’s lab and the first author of the paper, in a news release.

The team found that the energy source adenosine triphosphate, structural elements such as microtubules, and the motor protein dynein were required to form the structures, while the microfilament actin, normally essential for cell functioning, was not. Additionally, different concentrations of sperm nuclei affected the final shape and size of the cell-like structures and caused them to undergo cell division.

When sperm was added in high concentrations, compartments did not form at all, and at low concentrations, some compartments did not form nuclei. Ruptured eggs that received an intermediate amount of sperm were uniform in size, and almost all resulting cell-like formation contained nuclei. While sperm can affect the structures’ outcome, the research suggests that eggs are ultimately responsible for the development of basic spatial organization in cells. 

X. Cheng et al., “Spontaneous emergence of cell-like organization in Xenopus egg extracts,” Science, doi:10.1126/science.aav7793, 2019. 

Emily Makowski is an intern at The Scientist. Email her at