What goes wrong when photoreceptors cease their proper functioning? As my interests in photopigments continued to grow, I began photochemical investigations of Drosophila visual pigments using microspectrophotometry. I worked with Doekele Stavenga Fall, 1978. I became Associate Professor of Biological Sciences at The University of Missouri - Columbia in 1979, where I maintained NSF and NIH funding to investigate retinal degeneration and photoreceptor maintenance mainly in Drosophila (Stark et al., 1985). Several mutations, as well as intense light treatments, cause retinal degeneration in the fruit fly. In mutants of the rdgB gene, retinal degeneration can be initiated by one controlled light stimulus, making this strain a unique model of light induced hereditary degeneration among animals.

My studies have continued to the present time. Drosophila are now known to have 6 opsins that have been cloned. Fly stocks from Charles Zuker and Steve Britt helped me to visualize visual pigments and rhodopsin - metarhodopsin conversions for all 6 (Stark and Thomas, 2004); many of the figures that were on this page have been deleted since they are now in the above referenced publication.

When he worked in my lab, De-Mao Chen obtained useful electrophysiological data on transgenic flies where Rh2, Rh3 and Rh4 replaced Rh1 in R1-6:

1. Spectral sensitivities of white (w) eyed strains and one red (r) eyed strain.
2. ERG waveforms fro w Rh(1+4) [and for w Rh(1+3) not shown] as a function of intensity. For UV, they show good isolation of R1-6 (which generates on- and off-transients in the lamina ganglionaris). For blue, R8 (which bypasses the lamina) has a substantial input, and transients are smaller.

"Memoirs"

Using the deep pseudopupil, I could photograph the conversion of the blue-absorbing rhodopsin (R480) to yellow absorbing metarhodopsin in the deep pseudopupil of a live white-eyed Drosophila (Stark & Johnson,1980). Before I obtained this good picture, a lower quality picture seemed important enough that Doekele Stavenga used it in his chapter in the Handbook of Sensory Physiology (Chapter 7, Vol VII/6A, H. Autrum, ed. Berlin, Springer, 1979). At the time, I was worried since I was coming out in print with a disagreement with an explanation of this "darkening" published by a very influential researcher (Lo and Pak, Nature, 273, 772-774, 1978). When I visited Prof. Kuno Kirschfeld's lab (at the Max Planck Institute for Cybernetic Biology in Tubingen) in 1978, I was shown that he also saw this darkening and disagreed with the Lo and Pak explanation.

References:

The debut paper addressed to retinal degeneration in Drosophila-

Harris, W.A. and Stark, W.S. Hereditary retinal degeneration in Drosophila melanogaster: A mutant defect associated with the phototransduction process. The Journal of General Physiology, 1977, 69, 261-291. PubMed

The paper which introduced microspectrophotometry of visual pigments in the deep pseudopupil of Drosophila-

Stark, W.S. and Johnson, M.A. Microspectrophotometry of Drosophila visual pigments: determinations of conversion efficiency in R1-6 receptors. Journal of Comparative Physiology, 1980, 140, 275-286

Toward the end of a series of papers where microspectrophotometry was applied to quantifying retinal degeneration:

Stark, W.S., Walker, K.D. and Eidel, J.M. Ultraviolet and blue light induced damage to the Drosophila retina: microspectrophotometry and electrophysiology. Current Eye Research, 1985, 4, 1059-1075. PubMed

A recent comprehensive paper on the study of six Drosophia rhodopsins with various microscopic and optical techniques:

Stark, W. S., Thomas, C. F. Microscopy of multiple visual receptor types in Drosophila, Molecular Vision, 2004, 2004; 10:943-955, Full paper on line.

This page was last updated on July 29, 2005

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