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Lisa L. Cunningham, Federico Gonzalez–Fernandez; Coordination between Production and Turnover of Interphotoreceptor Retinoid-Binding Protein in Zebrafish. Invest. Ophthalmol. Vis. Sci. 2000;41(11):3590-3599.
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purpose. Interphotoreceptor retinoid-binding protein (IRBP), which is secreted
by the photoreceptors of most vertebrates, is the major soluble protein
component of the interphotoreceptor matrix (IPM). Recent studies
suggest that IRBP is short lived in the IPM (half-life, ∼11 hours).
The mechanisms coordinating the production and removal of IRBP are not
known. Zebrafish provide a useful system to study the regulation of
these two processes, because its IRBP mRNA levels are under circadian
regulation. In the present study, the relationship between the quantity
of IRBP, the rate of its turnover, and the expression of its mRNA in
the zebrafish retina were examined.
methods. Full-length zebrafish IRBP was expressed in Escherichia
coli and an antiserum generated against purified recombinant
IRBP. Western and protein dot blot analyses and indirect
immunofluorescence were used to define the temporal and spatial
patterns of IRBP expression in the adult zebrafish. In vivo and in
vitro metabolic labeling experiments were used to examine the
regulation of IRBP turnover by both environmental light and the
results. Despite the known rhythmicity in IRBP mRNA expression, neither the
amount of IRBP nor its localization changes significantly during the
light–dark cycle. IRBP is rapidly removed from the zebrafish eye (half
life, ∼7 hours). This rapid turnover is independent of environmental
lighting conditions during subjective day and is more rapid during the
day than at night.
conclusions. Because the amount of IRBP remains constant throughout the day, the
enhanced daytime IRBP mRNA expression may function to compensate for an
increased turnover of the protein during the day. These findings
suggest that the processes of IRBP production and removal are
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