Abstract
Studies were conducted to explore the tissue- and cell-specific regulation of cellular retinoic acid-binding protein (CRABP) expression in the rat. Two studies were carried out. The first explored the regulation of CRABP mRNA levels in selected rat tissues by dietary retinoid status, and the relationship between CRABP mRNA and protein levels in different tissues. The second examined the cellular localization of CRABP expression in the testis. In order to conduct these experiments, a cDNA encoding CRABP was isolated and characterized. The DNA sequence of the coding region had 96% identity with that of the mouse CRABP cDNA and encodes a protein identical to mouse and bovine CRABP. CRABP mRNA and protein levels were quantified in five tissues from normal, retinoid-deficient, and retinol-repleted rats. Tissue CRABP and CRABP mRNA levels were highly correlated (P less than 0.01) indicating that inter-tissue variability of CRABP levels mainly results from regulation of CRABP mRNA levels. Neither CRABP protein nor mRNA levels were affected by retinol deficiency, in marked contrast with results previously demonstrated with cellular retinol-binding protein (CRBP) (J. Lipid Res. 1990. 31: 821-829). 35S-labeled CRABP cRNA probes were used to localize CRABP mRNA within the testis of adult rats by in situ hybridization. CRABP mRNA was localized selectively in the periphery of the seminiferous tubules, primarily in type A spermatogonia. The localization of CRABP mRNA differs from that of CRABP protein, which is known to be enriched in maturing and more mature germinal cells. This difference suggests that CRABP in germ cells may be highly stable, remaining in the maturing germ cells without degradation long after CRABP mRNA levels have declined to very low levels. The specific localization of CRABP mRNA and protein presumably reflects the biological roles of retinoic acid in the development and/or later function of germinal cells.
Highlights
Studies were conducted to explore the tissue- and cell-specific regulation of cellular retinoic acid-binding protein (CRABP) expression in the rat
We report that CRABP mRNA is localized primarily to type A spermatogonia within the testis
Its 3' end falls one nucleotide short of the polyadenylation signal found in mouse and bovine CRABP cDNA (6)
Summary
Studies were conducted to explore the tissue- and cell-specific regulation of cellular retinoic acid-binding protein (CRABP) expression in the rat. CRABP mRNA and protein levels were quantified in five tissues from normal, retinoid-deficient, and retinol-repleted rats. The specific localization of CRABP mRNA and protein presumably reflects the biological roles of retinoic acid in the development and/or later function of germinal cells.-Rajan, N.,G.L.Kidd, D. Retinoids in the cytoplasm are normally found associated with specific intracellular retinoidbinding proteins (14) One of these proteins, cellular retinol-binding protein (CRBP) binds retinol and does not bind retinoic acid; another related protein, cellular retinoic acid-binding protein (CRABP), binds retinoic acid and does not bind retinol. These binding proteins are thought to be involved in the cellular uptake and in the intracellular transport and metabolism of their retinoid ligands They may play a role in the functional expression of their retinoid ligands. CRABP may be involved in regulating the transport of retinoic acid to the nuclear retinoic acid receptors which in turn mediate retinoid effects on gene expression
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