Muscle Cell Growth Mystery Unveiled: Breakthrough Discovery

Biophysicists at Emory University have uncovered a fundamental molecular mechanism in muscle formation, resolving a four-decade-old mystery regarding how actin filaments maintain their length and function, according to research published in July 2026 in Nature Communications. The discovery challenges a long-standing scientific paradigm and could aid in the design of future treatments for heart failure conditions like dilated cardiomyopathy.

Challenging a Four-Decade Muscle Formation Paradigm

For more than forty years, the scientific model of actin filament growth relied on a standard process known as treadmilling. In non-muscle cells, actin subunits continuously degrade and break off at the pointed minus end while freshly energized subunits add to the barbed plus end. However, muscle cell sarcomeres cap their plus ends with a protein, preventing new molecule addition while the filaments still manage to grow, replenish, and remodel themselves.

“We’ve made a fundamental advance in understanding how the cellular cytoskeleton is assembled, especially in muscle cells,” says Shashank Shekhar, assistant professor of physics at Emory University and senior author of the study. Shekhar’s team upended the traditional model by demonstrating that the protein leiomodin can build actin filaments from the pointed end, a mechanism previously thought impossible.

Microfluidic Microscopy Reveals Pointed-End Actin Growth

To investigate how heart muscle cells remodel their actin, Emory PhD candidate and first author Sudipta Biswas focused on leiomodin 2, a protein found near the pointed ends of actin filaments in cardiac muscle cells. Previous laboratory dish experiments showed that deleting leiomodin 2 makes actin filaments shorter, while an excess causes them to grow longer than normal.

Biswas utilized microfluidic-assisted total internal reflection fluorescence microscopy (mf-TIRF), a specialized technique used by only a handful of labs worldwide. By attaching red and green fluorescent tags to single protein molecules, the researchers tracked individual molecules moving through a microfluidic chamber. As green-tagged actin molecules were introduced, they anchored to the leiomodin base and gradually displaced the older red molecules, providing direct molecular evidence that actin filaments grow directly from their pointed ends.

Implications for Dilated Cardiomyopathy and Heart Failure

The discovery provides a concrete mechanical explanation for how genetic mutations disrupt the heart’s contractile machinery. A genetic mutation in leiomodin 2 is linked to dilated cardiomyopathy, a progressive condition that weakens heart muscles and impairs blood-pumping efficiency by producing abnormally short or long thin filaments.

“We also provide a molecular explanation for how defects in leimodin can disrupt the assembly of the contractile machinery of the heart,” says Biswas. By understanding precisely how these mutations cause structural defects at the cellular level, researchers have established a vital first step toward developing targeted therapies for heart disease. The study was supported by grants from the National Institute of General Medical Sciences and the National Heart, Lung, and Blood Institute.

Frequently Asked Questions

What is the role of actin in muscle cells?

Actin forms specialized, highly stable arrays called sarcomeres in muscle cells. These filaments slide past myosin to enable muscle contraction.

Why is actin filament length important?

Muscle contraction efficiency is directly controlled by the precise length of actin filaments, which remains tightly regulated from birth to death.

How does leiomodin 2 affect heart muscle?

Leiomodin 2 is found near the pointed ends of actin filaments in cardiac muscle and plays a key role in their assembly and remodeling. Mutations in this protein are linked to dilated cardiomyopathy.

What funding supported this research?

The research published in Nature Communications was fully financed with federal funds from the National Institute of General Medical Sciences and the National Heart, Lung, and Blood Institute.