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