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: Pathology
Which of the following protein is involved in intercellular connections? 
Select and explain. 
A. Connexin, B. Integrin, C. Adhesin, D. None of the above
A: Connexin
Answer: A: Connexin 
Explanation: Connexins is a protein involved in intercellular connections. It is an integral membrane proteins with four transmembrane domains, two small extracellular loops, a cytoplasmic loop and cytoplasmic N and C terminal tails. Connexins assemble into a hexamer in the plasma membrane forming a unit referred to as connexon or hemichannel. When two connexons on appositional cell membrane dock to each other, a gap junction channel is formed. Ref: Principles of Bone Biology By John P. Bilezikian, 3rd Edition, Page 430 ; Cell and Molecular Biology: Concepts and Experiments By Gerald Karp, 6th Edition, Page 239 ; Microbiology: An Introduction, 9th Edition By Toora, Page 455