Solid or liquid? Scientists accurately predict complex tissue changes in fruit fly embryos

Funded by the U.S. National Science Foundation, scientists have accurately modeled particular cellular changes in Drosophila melanogaster, or the fruit fly, during embryonic development. When certain tissue shrinks dramatically to close a gap during the fruit fly embryo's growth, the cells remain elastically solid rather than turning into a liquid form as expected. The model created by the researchers shows how this phenomenon happens and may lead to a new form of condensed matter physics with potential applications in neuroscience, biology and artificial intelligence.

The findings, published in Proceedings of the National Academy of Sciences, also revealed a surprising connection to the work that earned the 2024 Nobel Prize in physics.

"During the dorsal closure process, tissue, called amnioserosa, is shrinking like mad, and by all accounts, it should turn into a fluid," says Andrea Liu, University of Pennsylvania theoretical physicist and author on the research. "But it doesn’t. The cells stay locked in place with their neighbors, and we wanted to understand why."

The researchers used a method introduced by John Hopfield, who shared the 2024 Nobel Prize in physics with Geoffrey Hinton for their work developing computer technologies that mimic an organic brain's ability to process information.

"Hopfield, essentially, applied physics to neuroscience and created a subfield of the discipline, as well as the basis of neural networks," Liu says about the seminal work that laid the foundation for artificial intelligence. "He showed that by allowing the interactions between neurons to be individually adjustable, you could build a model of how the brain learns. So, we introduced tunable interactions among cells to see how a tissue of cells might remain rigid."

By incorporating this concept into their novel model of fruit fly tissue, the team was able to predict changes in cell shape, orientation and other properties that were later confirmed through additional experimentation. Liu believes this work points to a new category of condensed matter, one in which interactions between particles or cells are individually tunable rather than fixed.

"In conventional condensed matter physics, you can’t and don’t change interactions. They are what they are," Liu says. "But in biological systems, interactions are dynamic."

"In systems with tunable interactions, scaling up can produce entirely new, emergent properties. The behavior of a system with a million interacting units can be vastly different from one with thousands."

"This work beautifully combines features of biology, artificial intelligence and condensed matter physics to address a fascinating problem at the interface of biology and materials research," says Daryl Hess, program director in the NSF Division of Materials Research.