Embryonic Synthesis of the Inner Limiting Membrane and Vitreous Body

The inner limiting membrane (ILM) and the vitreous body (VB) are major parts of the extracellular matrix of the eye. The present study was undertaken to investigate the synthesis and turnover of the ILM and VB in chick and human embryonic and postembryonic eye development. The abundance of ILM and VB proteins was determined by Western blot analysis using samples from chick and human VB of different ages. The mRNA expression of the ILM proteins in lens was determined by in situ hybridization and RT-PCR. Based on the abundance of mRNA expression, the prominent sources of ILM and VB proteins in chick eyes are the lens and ciliary body. In chick, ILM and VB matrix proteins were most abundant in embryonic VB, and their concentration declined precipitously after hatching. Most ILM and VB proteins were no longer detectable in the adult VB. In humans, a similar developmentally regulated expression of ILM and VB proteins in VB was detected: The highest concentrations of ILM and VB proteins were detected in fetal VB, the lowest in the adult VB. The decline in ILM and VB protein synthesis occurred within the first 2 years of life. The abundance of ILM and VB proteins in the embryonic VB, their sharp decline at postembryonic stages, and their very low abundance in the adult VB show that ILM and VB are assembled during embryogenesis and are maintained throughout life with minimum turnover.