23 January 2020
Inner ear membrane development similar to 3D printing
Published online 27 November 2019
An inner ear membrane is anchored to the cell surface during development and grows one layer at a time.
A new study suggests that the multi-layered tectorial membrane, which is present in the inner ear and central to hearing, forms in a way similar to 3D printing, with successive layers growing on a cell surface. This mechanism may also underlie the development of other structures.
The prevailing hypothesis suggests that the components of the tectorial membrane are released into the network of molecules surrounding cells, known as the extracellular matrix, and then begin to self-assemble. But Sungjin Park of the University of Utah and his team weren’t convinced. “We reasoned that the tectorial membrane is too complex to be organized solely by an extracellular assembly process,” he explains. “We looked for an alternative model and observed that the border between the cell and the extracellular matrix plays a critical role in tectorial membrane morphogenesis.”
His team, including Ali Almishaal, who is currently affiliated with Saudi Arabia’s University of Hail, hypothesized that TECTA, a protein anchored to the cells on which the tectorial membrane develops, might guide tectorial membrane development by preventing its components from diffusing into the extracellular space. To test this, they engineered a version of TECTA lacking the anchor that tethers it to the cell. They found that mice with the mutated TECTA protein formed a severely disorganized tectorial membrane that was detached from its normal location.
Next, the researchers made a version of TECTA that was attached to the membrane by a transmembrane domain rather than the usual anchor domain. This led to the accumulation of tectorial membrane components on the cell surface, but because TECTA release was impaired, the tectorial membrane didn't develop into a multi-layered structure.
Based on these findings, the researchers suggest that the tectorial membrane forms via a process similar to 3D printing. TECTA on the cell surface serves as an organizer for tectorial membrane components; once a layer is formed, TECTA is released and the next layer is ‘printed’ underneath it, eventually resulting in a multi-layered architecture.
These findings not only clarify how the tectorial membrane develops but could also shed light on other structures that develop in the extracellular matrix. “The proposed 3D printing model will provide a novel insight into our understanding of extracellular matrix morphogenesis process during development and tissue repair,” says Park.
Kim, D-K. et al. The release of surface-anchored α-tectorin, an apical extracellular matrix protein, mediates tectorial membrane organization. Sci. Adv. 5, eaay6300 (2019).