Mutually exclusive expression of human red and green visual pigment-reporter transgenes occurs at high frequency in murine cone photoreceptors

摘要

This study examines the mechanism of mu- tually exclusive expression of the human X-linked red and green visual pigment genes in their respective cone photore- ceptors by asking whether this expression pattern can be produced in a mammal that normally carries only a single X-linked visual pigment gene. To address this question, we generated transgenic mice that carry a single copy of a minimal human X chromosome visual pigment gene array in which the red and green pigment gene transcription units were replaced, respectively, by alkaline phosphatase and #beta#-galac- tosidase reporters. As determined by histochemical staining, the reporters are expressed exclusively in cone photoreceptor cells. In 20 transgenic mice carrying any one of three inde- pendent transgene insertion events, an average of 63 or expressing cones have alkaline pbosphatase activity, 1O have #beta#-galactosidase activity, and 27 have activity for both re- porters. Thus, mutually exclusive expression of red and green pigment transgenes can be achieved in a large fraction of cones in a dichromat mammal, suggesting a facile evolution. ary path for the development of trichromacy after visual pigment gene duplication. These observations are consistent with a model of visual pigment expression in which stochastic pairing occurs between a locus control region and either the red or the green pigment gene promotor.