This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
The most impoant function of Major Intrinsic Protein 26 (MIP-26) is: 
Select and explain. 
A. Diffusion barrier, B. Capsule of lens, C. Glucose transpo in lens, D. Transpo of water in lens
D: Transpo of water in lens
Answer: D: Transpo of water in lens 
Explanation: Major Intrinsic Protein 26 (MIP-26), now known as Aquaporin 0 is found only in the plasma membrane of eye lens fibre cells. Its main function is to maintain transparency of the lens by maintaining a tight cellular junction and/or by water cirulation. Ref: Encyclopedia of Molecular Pharmacology, Volume 1, Springer, 2008, Page 215; Current Medicinal Chemistry Jun 1999, Page 465