In the fly, thorough retinoid deprivation is possible, optimizing investigation of the effects of vitamin A metabolites and retinoic acid [RA] on the visual system. Retinoids had been found to control fly opsin gene transcriptionand translation. To follow this line of inquiry, we examined the effect of retinoids on the translation and transcription of a Drosophila retinoid and fatty acid binding glycoprotein (RFABG) in collaboration with several workers at the National Eye Institute, especially Dr.Barbara Wiggert and Dr. R. Krishnan Kutty. Western blots, performed by Dr. Wendy L. Picking in my laboratory, showed that RFABG is high in retinoid replete flies and low in deprived flies. Flies grown on media containing alternative substances including retinoic acid yielded extracts containing significant amounts of RFABG. Immunocytochemistry, done by K. Shim, a Ph.D.student in my laboratory (Ph.D., Saint Louis University, 1997), confirmed the absence of RFABG in deprived flies and its presence in flies reared or replaced on diverse media containing retinoids or general nutrients. Further, immunocytochemistry localized RFABG to the Semper [cone] cells and the intraommatidial matrix [the interphotoreceptor matrix of the ommatidium]. Positive staining in Semper cells of ninaE and glass mutants suggests that RFABG does not depend on presence of Rh1 [R1-6 opsin] and that it is synthesized in Semper cells respectively. Some of the immunocytochemistry involved confocal microscopy in collaboration with Charles F. Thomas of The LOCI (Laboratory for Optical and Computational Instrumentation). Northern blots suggested the presence of RFABG mRNA in flies grown on normal food but not in flies grown on deprivation food. Although the synthesis of RFABG does not require chromophore precursors as does that of opsin, the control of RFABG and opsin transcription by retinoids including retinoic acid might very well be the same. Our results suggest that RFABG may be a functional homologue of the vertebrate IRBP [Interphotoreceptormatrix Retinoid Binding Protein] in retinoid transport. Also, Semper cells may be analogous to vertebrate RPE [retinal pigment epithelium] in retinoid metabolism and / or delivery.

A chapter putting this work into a broad perspective:

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.

A paper on this work:

Shim, K., Picking, W. L., Kutty, K., Thomas, C. F., Wiggert, B., Stark,W. S. Control of Drosophila retinoid and fatty acid binding glycoprotein expression by retinoids and retinoic acid: Northern, western and immunocytochemical analyses. Experimental Eye Research, 1997, 65, 717-727. PubMed

A western blot (from Shim et al., 1997) showing RFABG to be high in retinoid replete flies, low in deprived flies, and high in retinoic acid, yeast, beta carotene, and beef brain heart infusion flies as well as in ninaE mutants lacking the opsin of R1-6 receptors

A micrograph from Kyuhwan Shim's Ph.D. thesis work with bright staining in 4 Semper cells (right), not photoreceptor rhabdomeres (top left)

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This page last revised on June 28, 2005