A team from the Institute for Neurosciences (IN), a joint center of the Spanish National Research Council (CSIC) and the Miguel Hernández University (UMH) in Elche, has revealed how a structure essential for fly flight, the haltere, is formed. This small organ, located behind the main wings, functions as a biological gyroscope that helps the insect stay stable in the air. The study, published in the journal Current Biology , was led by researcher José Carlos Pastor Pareja, head of the Cell-to-tissue architecture in the nervous system laboratory at the IN.
This work shows that, contrary to previous assumptions, the haltere is not a hollow structure. Instead, its two surfaces are internally connected by a sophisticated cellular system that stabilizes its rounded shape. "This structure is a stabilization system reminiscent of architectural supports: without these internal connections, the haltere elongates and loses its shape, like a tent without guy ropes", explains Pastor Pareja.
During the process known as metamorphosis—from larva to adult—the wings and halteres develop from a thin layer of cells. In the case of the haltere, the team discovered that an extracellular matrix rich in collagen, which separates its two surfaces, is first degraded. This degradation enables the formation of cellular projections that connect both surfaces through a matrix containing another protein, laminin, thereby forming an internal framework.
These connections act as biological tensors that resist the forces that would otherwise deform the organ. When this system fails, as seen in genetically modified fruit fly (Drosophila melanogaster) models created by the team, the haltere loses its rounded shape, which is key to its function. The study also reveals that the haltere is under constant tension: one force pulls at its base, while another anchors it to the insect's outer cuticle. It is precisely this internal tensor system that balances both forces to maintain the haltere's geometry.
To observe these effects, the team used advanced electron microscopy and live imaging techniques during fly metamorphosis. "We observed a series of cellular projections that stabilize the rounded shape of the haltere by counteracting forces that would otherwise deform it," says Pastor Pareja, adding, "When we removed this supporting structure in mutant models, the organ lost its functional geometry."
The use of mutant models and analysis of the extracellular matrix were key to uncovering this mechanism, which combines collagen degradation, cell adhesion, and internal tensors that reinforce the structure from within. The findings go beyond the specific case of the fruit fly, offering general insights into how organs acquire their shape in animals, a fundamental question in developmental biology. Furthermore, they may inspire new approaches to issues such as tissue engineering or the design of biomimetic structures.
The study was conducted in collaboration with researchers Yuzhao Song and Tianhui Sun from Tsinghua University (China); Paloma Martín and Ernesto Sánchez Herrero from the Severo Ochoa Molecular Biology Center (CBMSO-CSIC-UAM); and Jorge Fernández Herrero from the University of Alicante. This work was supported by funding from the Spanish Ministry of Science, Innovation and Universities, the Severo Ochoa Centers of Excellence Program at the Institute for Neurosciences CSIC-UMH, the Ramón Areces Foundation, and the National Natural Science Foundation of China.
