Does vitamin A deprivation and replacement regulate opsin, sensitivity and retinoid binding protein in the vertebrate as it does in Drosophila? In the fly, carotenoid deprivation and replacement are relatively straightforward manipulations; in the vertebrate this is not the case, which may explain the relative paucity of such data in higher animals. The long-standing dogma for the rat was that deprivation leads to degeneration, but this was disproved in experiments in collaboration mainly with Prof. Martin L. Katz, Department of Ophthalmology, University of Missouri and Prof. Richard H. White, Department of Biology, University of Massachusetts - Boston. Vitamin A's control of opsin is strikingly different in the fly vs. rat. Deprivation for 26 weeks decreases rhodopsin by over 85% as measured spectrophotometricallybut it does not decrease opsin density as determined by P-face particle counts or quantification of EM immunogold labeling of an opsin antibody. However, the volume of the outer segments is reduced to 42%. Upon administration of vitamin A to deprived animals, the opsin in these diminished outer segments recovers rapidly to functional rhodopsin; moreover, the outer segments recover in about two weeks, a time frame consistent with the turnover of an outer segment, as judged mainly by electroretinographic recording done by D.-M. Chen, in my laboratory. Because of the increasing use of transgenic mice in research, Profs. Katz and Chen and I joined forces with Prof. G. I. Liou of the Ophthalmology Department of the Medical College of Georgia to pursue the vitamin A deprivation and replacement experiments in mice. We found that vitamin A deprivation decreases interphotoreceptor matrix binding protein (IRBP), but does not affect IRBP's mRNA.
I would do my duty and give an occasional seminar to my
ophthalmology group at Missouri, though I doubted they were much
interested in Drosophila. Several times, I would show the freeze-fracture
picture of high vs. low vitamin A Drosophila -- rhabdomeric microvilli
in deprived flies were intact but low in protein. Each time, Lynette
Feeney-Burns would remark, "Isn't that odd. In rats, receptors
degenerate" as shown by the famous John Dowling and George
Wald at Harvard. When Marty Katz had arrived at Missouri, he said,
"Not so fast! I vitamin A deprive rats to manipulate the
aging pigment lipofuscin, and the receptors are still there."
We all agreed, "Wouldn't it be interesting to see if vitamin
A deprived rat rods also lose their opsin?" We enlisted the
help of Dick White at U Mass - Boston who had a modern freeze-fracture
replica maker and whose interest in vitamin A deprivation in moth
receptors made him a great colleague. I stopped off for a long
weekend in Boston before a meeting at Cold Spring after Marty
and I had sent frozen samples. We had the answer in 4 days (freeze-fracture
density was high in deprived rats in contrast with the fly situation)
and we express mailed slides to Marty for a talk he was giving
later that week. Since, in fact, the rat rods did not degenerate,
contradicting Dowling and Wald's result, I was nervous but excited
when Dowling came to my poster at the Association for Research
in Vision and Ophthalmology (ARVO). He was cordial and polite,
so the visit was not an ordeal. Later, when we published in Investigative
Ophthalmology and Visual Science (IOVS), the referees complimented
us for the quality of our work. Eventually, in collaboration with
my long-time coworker and friend De-Mao Chen, we found that vitamin
A deprived rats recovered when given replacement therapy, further
substantiating the integrity (with lower sensitivity) of rods
of vitamin A deprived rats.
Vertebrate vitamin A deprivation and replacement papers:
Katz, M. L., Gao, C.-L., Kutryb, M., Norberg, M.,Gao, C.-L., White, R. H., Stark, W. S. Maintenance of opsin density in photoreceptor outer segments of retinoid-deprived rats. Investigative Ophthalmology and Visual Science,1991, 32, 1968-1980. PubMed
Katz, M. L., Chen, D.-M., Stientjes, H. J., Stark, W.S. Photoreceptor recovery in retinoid-deprived rats after vitamin A replenishment. Experimental Eye Research 1993, 56, 671-682. PubMed
Liou, G. I., Matragoon, S., Chen, D.-M., Gao, C. L., Zhang, L., Fei, Y., Katz, M. L. Stark, W. S. Visual sensitivity and interphotoreceptor retinoid-binding protein in the mouse: Regulation by vitamin A. The FASEB Journal, 1998,12, 129-138. PubMed, Full paper on-line, View pdf file
Stark, W. S. Comparative biology of receptor recovery by retinoid replacement in retinoid deprived flies and rodents. In Degenerative Retinal Diseases (eds. M. M. LaVail, J. G. Hollyfield, R. E. Anderson), New York, Plenum, 1997, 135-143.
Transmission electron micrographic longitudinal and cross sections showing that rods in vitamin A deprived rats are smaller than in vitamin A replete rats (from Katz et al., 1991)
A freeze fracture micrograph of a rod from the Katz et al 1991 work showing that the opsin density was the same in vitamin A deprived (B) and replete (A) rats.
Vitamin A replacement therapy causes an immediate recovery of ERG sensitivity (suggesting that opsin can accept chromophore) and a full recovery in 2 weeks (suggesting that rod outer segments can grow back to full size).
In this demonstration of vitamin A mediated recovery of sensitivity in deprived mice, it is also clear that deprivation preferentially affects the UV cones (Liou et al.).
IRBP, as shown here
as immunogold, is decreased by vitamin A deprivation and recovered
by repletion (Liou et al.).
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This page was last updated June 14, 2005