The Generation of Knock–In Mice Having Green Cone Pigments in Rod Photoreceptor Cells

Abstract

Purpose: : Most vertebrate retina contains two types of photoreceptor cells, rods and cones. Cones have lower photosensitivity and faster photoresponse kinetics than rods. Since these photoreceptors have similar but different phototransduction proteins, the differences in the photoresponses are thought to be originate from the properties of phototransduction proteins. To examine whether the different characteristics of rod and cone visual pigments contribute to the difference in photoresponse, we have generated knock–in mice in which rod visual pigment (rhodopsin) was replaced by the mouse green–sensitive cone pigment (mouse green).

Methods: : The mouse Green cDNA sequence was introduced into mouse rhodopsin loci by knock–in technology. Transcriptional and translational products were investigated by RT–PCR and Western blot analyses. Expression and localization was visualized by immunohistochemistry. Photoresponses from photoreceptors were recorded by the suction electrode methods.

Results: : The replacements of transcripts and proteins were achieved dependent of the genotype of rhodopsin locus. The expression pattern of mouse green from knock–in allele is apparently under the endogenous regulatory control and mouse green is successfully transported to the rod outer segments. We were able to record photoresponses of mutant rods. The sensitivity of mutant rods was found to be lower than that of wild type.

Conclusions: : These results suggest that mouse green cone pigment expressed in rods can function and is correlated with lower sensitivity of cone photoreceptors.

Keywords: opsins • photoreceptors • signal transduction