One gap junction consists of a cluster of closely packed pairs of transmembrane channels, the connexons, through which materials of low MW diffuse from one cell to a neighboring cell. Involved in tracer coupling between horizontal cells of the retina. May play a role in the regulation of horizontal cell patterning. A connexon is composed of a hexamer of connexins. Low levels were detected in skin, heart, kidney, testis, ovary, intestine. Expression not detected in brain, sciatic nerve or liver. According to PubMed:15147297 expression is detected only in horizontal cells in the inner nuclear layer of the retina and not in other neurons of the central nervous system or tissues. Detected in the outer plexiform layer of the retina (at protein level). Expressed in the retina from 16.5 dpc to P1, in the thymus from 18.5 dpc to P1, and in kidney from 16.5 dpc to 18.5 dpc. Mice are fertile and show no obvious anatomical or behavioral abnormalities. In horizontal cells of the retina tracer coupling is abolished but the spatial tuning of ganglion cells is unchanged. Belongs to the connexin family. Alpha-type (group II) subfamily.