Major intrinsic protein is a member of the water-transporting aquaporins as well as the original member of the MIP family of channel proteins. The function of the fiber cell membrane protein encoded by AQP-0this gene is undetermined, yet this protein is speculated to play a role in intracellular communication. The MIP protein is expressed in the ocular lens and is required for correct lens function. AQP-0 has been mapped among aquaporins AQP2, AQP5, and AQP6, in a potential gene cluster at 12q13.