Abstract
Purpose: :
The inner limiting membrane (ILM) is the basement membrane of the retina and separates the retina from the vitreous body. The ILM has been shown to play important roles in retinal histogenesis, the survival of ganglion cells and axonal navigation. Disruption of the ILM in embryonic chick and mouse embryos leads to retinal dysplasia and ganglion cell death. We investigated the mechanical and structural properties of the embryonic chick ILM during different stages of development.
Methods: :
We have examined the structural and elastic properties of freshly dissected, unfixed ILM from eyes of chick embryos using atomic force microscopy (AFM). The elasticity modulus of the ILM was measured by nano–indentation of ILM on a solid substrate as well as ILM suspended over a circular aperture.
Results: :
Previous TEM studies of ILM structure using dehydrated retinal sections gave estimates of the thickness of the ILM at approximately 50–70 nm. Using AFM, our present study shows that the thickness of hydrated chick ILM is ∼ 180 to 250 nm at embryonic day 4 (E4) and increases to ∼ 300–370 nm at E9. The biomechanical property of ILM also undergoes significant changes during development: the Young’s modulus of chick ILM is 0.5–0.6 MPa at E4; at E9 the Young’s modulus of ILM increases nearly two–fold to an average of 1.0 – 1.1 MPa.
Conclusions: :
This study provides the first direct measurements of the elastic properties of ILM, and demonstrates the changes in the thickness and the biomechanical property of ILM during development, which may have important implication for the retinal development and the axonal pathfinding.
Keywords: extracellular matrix • retina • development