OPN4 and intrahepatic cholangiocarcinoma: Overall, the results of our ICC studies using the Opn4L and Opn4S specific antibodies show a different profile of Opn4L and Opn4S expression over time during development, and based on our observations this differing pattern of expression would seem to correlate with the maturation of M1 and M2 type pRGCs (where maturation is defined as cells reaching adult levels of melanopsin expression).