Purchase this article with an account.
M. Najafi, P. D. Calvert; Recoverin Redistributes to Xenopus Rod Outer Segments in Response to Light. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5429.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To establish the subcellular localization patterns of recoverin (S-modulin) in Xenopus rod photoreceptors under dark- and light-adapted conditions. Recoverin (Rec) is a Ca2+ binding regulatory protein that undergoes light-dependent translocation within rod photoreceptors. The mechanism of light-dependent translocation and localization are not yet understood. We thus have studied the distribution of Rec-EGFP expressed in Xenopus rod photoreceptors under different light conditions.
Transgenic frogs expressing Rec-EGFP or unfused EGFP under the Xenopus opsin promoter were created by REMI. Retinal slices from dark-adapted animals were dissected under infrared illumination and placed into the recording chamber of a confocal microscope. Live cell 3D images were obtained before and at various times after illumination sufficiently intense to close all cGMP-activated channels. The spatial distributions of Rec-EGFP were measured and compared to those of unfused EGFP to identify sites of localization.
The distribution of Rec-EGFP differed from that of EGFP in both dark and light-adapted photoreceptors; in the dark ~57% of Rec is found proximal to the junction between inner and outer segments, primarily in the myoid, and ~43% is in the outer segment while in the light these ratios effectively reverse. In contrast, cells that express unfused EGFP contain ~50% of the total fluorescence in each of these regions. Thus light causes an ~1.3-fold increase in total Rec mass in the outer segment. The light-induced redistribution requires more than 1 hr to complete.
One interpretation of these results is that, owing to Rec’s Ca-dependent membrane affinity, its localization is mediated by Ca-induced binding to membranous structures that are abundant in the myoid, such as the endoplasmic reticulum. By extension the Ca2+ levels in the myoid region of the dark-adapted photoreceptor should significantly exceed those of neighboring compartments, e.g. the outer segment, in the dark-adapted rod and decline in response to light, thus releasing Rec. Our results differ from those obtained from mice with a different method and reported previously.
This PDF is available to Subscribers Only