Imaging technique reveals new structure in retinal cells

A new imaging technique used by a group of researchers at the University of Washington and elsewhere has revealed a previously unknown cellular structure in the retinas of mice. The structure is the site for an important part of the retinoid cycle, a chemical process critical to vision, the scientists said. Results of their study, which took more than three years, appeared in the Feb. 2 issue of the Journal of Cell Biology.

Dubbed a retinosome, the newly discovered organelle houses retinyl esters, which are an intermediate chemical product in the retinoid cycle. That cycle is critical in the regeneration process for 11-cis-retinal, a light-absorbing chemical vital to vision.

Dr. Yoshikazu Imanishi, senior research fellow in the UW Department of Ophthalmology, worked on the project with Dr. Kris Palczewski, Bishop Professor and professor of ophthalmology, chemistry, and pharmacology at the UW; Matthew Batten, a research scientist in Palczewski’s lab; and researchers from Vanderbilt University and the University of Utah.

Retina tissue doesn’t survive long outside of the eye, so Imanishi and his colleagues developed a technique to examine the tissue in a natural setting. They used a pulse laser to perform two-photon fluorescent microscopy on the retinas of live, anesthetized mice. The low-power, non-invasive technique allowed the researchers to examine the retina tissue within the eye without damaging it.

After discovering the previously unknown structure, the researchers isolated its role in the retinoid cycle through a chemical analysis. They also watched the retinoid cycle in normal mice and two types of transgenic mice, one without the ability to produce retinyl esters and the other unable to process the esters. Both the analytical chemical method and the genetic tests indicate that the retinosome houses retinyl esters for the retinoid cycle.

The researchers hope the new imaging technique will continue to boost understanding of the retina and the retinoid cycle. Since many types of congenital blindness are caused by defects in the retinoid cycle, the researchers hope their findings could one day help in clinical applications.