Rhodopsin Signaling and Organization in Heterozygote Rhodopsin Knockout Mice

• Published in: The Journal of biological chemistry 2004-11, Vol.279 (46), p.48189-48196
• Main Authors: Liang, Yan, Fotiadis, Dimitrios, Maeda, Tadao, Maeda, Akiko, Modzelewska, Anna, Filipek, Slawomir, Saperstein, David A, Engel, Andreas, Palczewski, Krzysztof
• Format: Article
• Language: English
• Subjects: Animals; Cell Membrane - chemistry; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Electroretinography; Lipid Metabolism; Lipids - chemistry; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Atomic Force; Retinoids - chemistry; Retinoids - metabolism; Rhodopsin - genetics; Rhodopsin - metabolism; Rod Cell Outer Segment - metabolism; Rod Cell Outer Segment - ultrastructure; Signal Transduction - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M408362200

Rhodopsin (Rho) resides within internal membrane structures called disc membranes that are found in the rod outer segments (ROS) of photoreceptors in the retina. Rho expression is essential for formation of ROS, which are absent in knockout Rho-/- mice. ROS of mice heterozygous for the Rho gene deletion (Rho+/-) may have a lower Rho density than wild type (WT) membranes, or the ROS structure may be reduced in size due to lower Rho expression. Here, we present evidence that the smaller volume of ROS from heterozygous mice is most likely responsible for observed electrophysiological response differences. In Rho+/- mice as compared with age-matched WT mice, the length of ROS was shorter by 30–40%, and the average diameter of ROS was reduced by ∼20%, as demonstrated by transmission and scanning electron microscopy. Together, the reduction of the volume of ROS was ∼60% in Rho+/- mice. Rho content in the eyes was reduced by ∼43% and 11- cis -retinal content in the eye was reduced by ∼38%, as determined by UV-visible spectroscopy and retinoid analysis, respectively. Transmission electron microscopy of negatively stained disc membranes from Rho+/- mice indicated a typical morphology apart from the reduced size of disc diameter. Power spectra calculated from disc membrane regions on such electron micrographs displayed a diffuse ring at ∼4.5 nm -1 , indicating paracrystallinity of Rho. Atomic force microscopy of WT and Rho+/- disc membranes revealed, in both cases, Rho organized in paracrystalline and raftlike structures. From these data, we conclude that the differences in physiological responses measured in WT and Rho+/- mice are due to structural changes of the whole ROS and not due to a lower density of Rho.