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
Universal marker of limbal epithelial stem cells: 
Select and explain. 
A. Elastin, B. Keratin, C. Collagen, D. ABCG2
D: ABCG2
Answer: D: ABCG2 
Explanation: Ans: D. ABCG2(Ref Indian J Med Res. 2008 Aug:128(2):149-56. PM1D:19001678; http://wwwstembook.org/node/588).ABCG2:Universal marker of limbal epithelial stem cells.Limbal Stem Cell Marker.Keratin (K3-K13) = Corneal Stem Cell Marker