Harvard: Scientists have solved a decades-old mystery about how our cells communicate with one another to build and maintain our bodies. They found that in order to converse in a language called Notch, the “speaking” cell must physically tug on the “listening” cell. The results of their research, which required combining specialties and inventing new experimental techniques, should help scientists better understand how cells convey information through Notch signaling. The findings are reported June 4 in Developmental Cell.
Notch is important for processes such as determining cell fate during
embryonic development. In addition, mutations of the gene encoding
Notch are found in some diseases, including more than half of all cases
of T-cell acute lymphoblastic leukemia (T-ALL).
The study could therefore inform researchers’ understanding of what
is going wrong in such diseases, said co-corresponding author Joseph Loparo, assistant professor of biological chemistry and molecular pharmacology at Harvard Medical School.
The tools the team created should help scientists investigate the
role physical force plays in regulating a variety of biological systems.
“Knowing that this ancient system for cell-cell communication has
built into it a dependence on mechanical force has relevance to the
fundamental question of how Notch signaling guides normal developmental
decisions in multicellular organisms, and should provide insight into
mutations that likely bypass the force requirement in disease,” said Stephen Blacklow,
the Gustavus Adolphus Pfeiffer Professor and chair of the Department of
Biological Chemistry and Molecular Pharmacology at HMS, who led the
study with Loparo.
“I am excited that our work provides new insights into Notch
signaling, and we hope that the tools we developed will be useful to our
colleagues in the Notch signaling field,” said Wendy Gordon,
who conducted the work as a postdoctoral researcher in the Blacklow
lab. Gordon is now an assistant professor at the University of
“Furthermore, altered mechanical forces in the microenvironment of
cells in disease states like cancer is an emerging concept that
necessitates new tools like the ones we developed to understand how
other proteins on the surface of cells use mechanical force to
communicate signals to the inside of cells,” she said.
Before this study, researchers understood the basic order of events needed to convey a Notch message. But pieces were missing.
They knew that a molecule called Delta on the surface of the
“speaking” cell binds to a molecule called Notch on the surface of the
“listening” cell. Then an enzyme swoops in, and, like a pair of
scissors, snips off a piece of Notch, releasing the signal into the
Notch’s “cut here” site is initially hidden. It wasn’t clear how it
becomes available to the enzyme scissors. Experiments showed that the
mere binding of Delta and Notch molecules wasn’t enough to expose it.
Fifteen years ago, scientists proposed that a mechanical force might
be needed. In the current study, Blacklow and Loparo’s teams became the
first to directly test the idea—and show that it’s probably correct.
“You need to pull on Notch,” said Blacklow.
To make their discoveries, the researchers first set up simplified
Notch systems on a glass slide. They attached tiny magnetic beads to
individual Notch molecules tethered to the slide and bathed them in the
At first, nothing happened. Then they used what they called magnetic
tweezers to pull on the beads. When they achieved enough force, the
Notch molecules were cut and the beads floated away.
“It was a really clever idea,” said Blacklow of Gordon’s experimental design.
pulled, fluorescently tagged magnetic beads are cut free of Notch and
float away. Experiment shown at 100 times normal speed.
The tests revealed that the force needed to reveal the cutting site was within the realm of what might occur in a real cell.
The researchers pursued their findings in a second set of experiments
conducted in real cells using complete Notch and Delta molecules. They
confirmed that magnetically tugging at Delta within a certain range of
forces revealed Notch’s cutting site and released the signal without
tearing apart either molecule.
Finally, the researchers built synthetic alternatives to the natural
Delta-Notch connections to test whether anything about the natural bond
other than the pull force might help expose the cutting site.
“Is it just a tether?” asked Loparo. “Or does something else in the connection lower the barrier to the door opening?”
Gordon designed one synthetic system. Norbert Perrimon, the James Stillman Professor of Developmental Biology at HMS, and members of his lab designed another.
Both systems showed that the pull force alone was sufficient to
reveal the cutting site and release the signal. The experiments also
revealed which parts of the Delta-Notch system are essential.
As they slot one more piece into the puzzle of Notch signaling, the
research teams look forward to exploring new questions their work has
“We came to this problem with two complementary areas of expertise,”
said Loparo. “Neither of our labs could’ve done this on their own. It’s a
fun and exciting way to do science.”
This work was supported by the National Institutes of Health (grants
R01 CA092433 and P01 CA119070) and the Howard Hughes Medical Institute.